Vibration at Idle

[dominicnwusa]

Hello everyone!

1990 2+2 NA

I've got an interesting one I was hoping someone with more knowledge could help me out with. I've been in the process of bringing my Z back to as close as I can to how it ran brand new. Unfortunately I have this incredibly aggravating shake/vibration at idle. This only used to happen after the car fully warmed up, Now its happening non stop and almost feels "rhythmic". Interestingly enough, sometimes i will pull up to a stoplight and it will idle beautifully, no shake at all. Idle loves to hang out at about 1k but will every now and then go a little above that or a where it should at 700. Shaking is more pronounced when not idling at 1k RPM. Car seems to run just fine while accelerating maybe some occasional hesitation once in a blue moon.

Heres what I've done so far:

Ohm'd the Injectors, all are at 13 (phase II swap done by PO)
Ohm'd the Coil Packs all at .7
Power balance test, no dead cylinders
ICAV was removed and liberally cleaned and replaced with a new gasket
90% of the vacuum lines have been replaced (all but the AIV lines)
Throttle bodies cleaned
Plenum grounds cleaned up
Knock sensor was bad so I relocated it
PTU replaced (no new subharness, could be my issue)
Coolant Temp Sensor and harness replaced
CAS and TPS connectors cleaned as they had minimal corrosion
unrelated: had the 120K and Clutch/flywheel/TO Bearing done professionally by a shop
as far as codes go im getting a 55, all clear there

Next thing I plan to do is go to habor freight and get myself a vacuum gauge to see if I can find any issues with the engine itself.

Thanks for any help guys!

[dominicnwusa]

I should mention too that I replaced both O2 sensors

[nissanfreak12]

Even though the injectors ohm good, there can still be a bad injector causing it. Did you notice when any little less difference when doing a power balance test?

I didn't see the following

Spark plugs
Fuel filter
Timing checked
Fuel pressure
Have you checked the Fuel pressure reg? try taking off the vac line and see if that raises the idle.

NOw is your EGR deleted?

AIV can cause a vacuum leak as well as a Vac leak through the EGR. Try blocking both those vac lines off and see what that does.

How long have you had this issue? Since the timing belt?

[dominicnwusa]

Hey NissanFreak thank you for the reply!

there was a HUGE difference in idle when doing the power balance test. Way worse than the slight vibrations im having.

Spark plugs are the proper NGK PFR6B-11 for an NA. I gapped them myself to .44 before handing them over to the Z shop to put in during the timing belt service. I do plan on pulling them within the next week to see how they are looking.

I did change out my fuel filter shortly after I got the car. Its a wix, so im not super thrilled and wish i just ordered a oem filter online. But autozone instant gratification....

I tried to check my timing, but my gun is either defective, or its not picking up at the plug wire. The Z shop said my timing was at a perfect 15 degrees before they did the service and was still at 15 degrees after. I did notice they made a scribe mark on the CAS.

I did not think to check the FPR, I can definitely do that, easy enough.

I went out and bought a vacuum / Fuel pressure gauge after work yesterday so I'll be able to test out the fuel pressure. I have thought my culprit could be the pump. For a while the car seemed to run amazing with a full tank of gas and then would have the crap idle when at about 1/4 tank.

My EGR is still intact and still original to my knowledge. I did block off the AIV vac lines a while back and noticed it made no difference so i just hooked it back up. I did not however think to cut the EGR vacuum off. I'll give that a shot as well.

I did notice this was not an issue until after the timing belt service. but it started weeks after the service had been done.

I'll try all these things in the coming week and get back to you. Thanks again!

[nissanfreak12]

Wix filter is a good brand, you are fine with that.

If you are having issues with less gas in the tank, its very possible you could have a lot of crap in the tank and causing it to clog the in tank filter. Most of the time fuel pump issues are at the higher RPM's. Do you have any problems during the driving range?

When checking the timing, you need to take the wires out of the sheath on the #1 coil pack and get I want to say the left wire in the hook part of the timing light. Just mess around with it until it starts to actually show as reading.

You could also having a sensor, CTS, that may be reading incorrectly but enough for it not to show up in the ECU.

Is your PRVR still intact? This going bad usualy causes hard starting, but it could cause idle issues as well.

Check for vac leaks in the pipes below the headlighs. If you stil have the plastic baffles still in place, that could cause issues you speak of.

[dominicnwusa]

The car seems to drive just fine under normal conditions and I have no issues getting it to higher revs whenever i feel like a spirited drive. Possibly unrelated if I'm in say, 4th gear, and am just below 2k RPM and I open it up I get this really low drone (almost like gravel/marbles) coming from what sounds like the engine bay. noise dissipates at about 2500K-ish. I've had plenty of manual cars and I know you get some disgruntled engine noises when accelerating hard from low revs but this is a bit different. I have a balanced aluminum driveshaft so I know thats not it.

Thank you for the tips on reading the timing, I'll be sure to try those. I was just trying to read over the sheathing.

I'm inclined to believe the CTS is good to go. I just replaced the sensor itself and the harness as the old one had some really nasty corrosion and a busted harness with no clip Needless to say I had a noticeable improvement there.

Haha, I was just reading about the PRVR today, funny you brought it up too. I'm going to use some extra vac line to bypass it and see how it works. I have been noticing cold starts have been getting a bit sketchy lately. Too sketchy for me in fact.

Good call on the piping below the headlights, I ordered some hardpipes because I'm either hearing a hiss or the alternator bearing making noise on the passenger side of the engine up front. It would be a good time to check the pipes when I install those, I have a POP Charger up front but the piping is all stock and original.

Once again, thank you for your input, it is greatly appreciated!

[nissanfreak12]

Hard pipes are a factory item and as far as I know they do not make aftermarket ones. The hard pipes you probably ordered replace the accordian pipes. You can remove all the plastic that attaches to the hard pipes. All they do is quiet the noise down. You can plug the bungs coming off the pipes, just go to home depot and I think they are 1 1/2" rubber caps in the plumbing department. Two of them will cost you about $5, works great and I have never had an issue with them.

PRVR basically is supposed to stop vapor lock. Nissan designed it with the 240z, but very rarely can you get vapor lock in a fuel injected engine, only if you drive a ford f350 with a 460 does that happen(ask me how I know). So you can delete it with confidence it wont happen.

Personally I think you have a vac leak which causes all the issues you are having. Look at those plastic pieces under the headlight and get rid of them. They are huge source for letting air in after the MAF.

[dominicnwusa]

Great! Yes I bought metal piping to replace the accordion pipes going to the throttle bodies. I had no idea about the extra piping attached to the pipes under the headlights, so thank you! Looks like i'll be pulling the bumper cover this upcoming week, needs to be re aligned anyway. Would I hear more of an induction noise once i plug the bungs? That would be nice.

I'm an IT guy with a hobbyist mindset, not really much of a mechanic so as always, I appreciate your time and knowledge.. Always willing to go out of my comfort zone to learn new things however. I'll be working on the car probably this weekend, I'll be sure to fill you in on any results or new findings!

[dominicnwusa]

Well, I have some updates... Not good ones I'm afraid. I did the PRVR bypass, It didn't change anything but Its good to have one less thing to worry about. I also was able to bypass the AIV system just to see if it would make a difference, but it didn't, so i hooked it back up. I was going to cap off the extra pipes you mentioned but ran out of time as I had to go pick up my sister from the SeaTac airport (this is my only car I own).

Got stuck in traffic because anyone who lives in the I-5 corridor knows you can never depend on getting somewhere without getting stuck in a traffic jam haha. Broke free of the jam and was cruising down the highway at about 3k when i felt a sudden almost jolt/buck/surge? I'm not sure what the right word to use would be. Look down and I have a CEL. So I pull off at the nearest exit to pull the code.

Shut the car off, pull the code: 55 .... WTF you are definitely not ok car....

Play around with a few other things under the hood. Nothing looks damaged or out of place. No leaking fluids, smoke or anything like that. try and start the car and I get the craziest hunting idle and lots of stalls. pulled o2 sensors just for good measure.... same thing. Figure this is something I don't want to tinker with and continue to drive on public roads. Thank God for triple A

Roasted in the Z for almost 2 hours before the tow truck gets to me. I had been just tinkering around in the interim and noticed my condenser fan is spinning like no other when i put the ignition in the ON position, I start the car up to see what its going to do and Its idling at 2k steady. much higher than normal (I had plugged the o2s back in at this point) Time to do a little research

To me it seems like the car put itself in safety mode due to overheating. The temp gauge didn't look any higher than normal while driving but, it is a dummy gauge.

I was a bit confused about why the car would overheat, it had been topped off by the Z shop not even 2k miles ago after the 120k service. Then it hit me... What if I have been having a small head gasket leak this WHOLE time? It used to only have that shake at idle when it was warm out, then it started happening when it was cold too. And now overheating to the point of safety mode? Perhaps, and i could be wrong, but would some coolant leaking into a cylinder cause that vibration I had been dealing with? The car ran like total garbage pulling it on and off of the tow truck, and has a horrid exhaust smell. I won't know the prognosis until probably Monday but I'm pretty worried, and perhaps a bit jumpy with my conclusions.

[nissanfreak12]

If the cooling fan runs continously with the key to the on position, and everything is stock(cooling system wise), the CTS is reading hot. Which means it is bad. It may not show up on the ecu, because it is still in the parameters.

Head gasket issue will also cause what you are talking about. That being said, there would have been more issues. The temp gauge is really not a dummy gauge, it is there to warn you if it is getting hot. If the temp goes up and down when cooling and heating, you are fine. Chances are it did not overheat. Chances are the CTS is reading that it is hot and told the ecu that, even though it didn't get hot.

Are you absolutely sure it didn't overheat?

[dominicnwusa]

My gauge needle was maybe a millimeter or two higher than where it normally sits (halfway)

It didn't seem any hotter than normal, but what freaked me out a bit was how bad it was running. Had to push the gas pedal quite a bit more than normal to keep it from stalling when i was moving it on and off the tow truck. It also was belching some dark exhaust when i pulled it into a parking spot at the auto shop I had to have it towed to. I'd love to think the CTS is garbage. Just replaced it a few weeks ago (autozone part) and Z1 patch harness hooked up with butt connectors.

[dominicnwusa]

Called the shop for a quick update. They said they are doing a block test on the car to check the integrity of the Head gaskets due to the white smoke coming out of the exhaust....I'll know more on Monday

[nissanfreak12]

I know white smoke is supposed to be water/coolant. Blue is oil and black is fuel. But I have honestly seen what looks like white smoke is fuel due to a faulty FPR, CTS , and injector.

When it was smoking, what kind of smell was it? Was it a sweetish smell? Fuel smell? Have them unplug the CTS and see if it makes a difference. It may run it a closed loop so it should run better if that is the issue. Have them try that first before telling you is a bad head/head gasket.

[DCaff300ZX]

Wow, so that was you on the side of I-5 the other day? I tried to pull over but as you said, the traffic...what a mess we have daily there in Fife!

My experience with similar issues that you speak of has centered around the PTU harness connectors (would have been moved and such during 120k service) and the IACV connectors/harness. Also at huge risk is the fuel injector connectors andinjectors, as mentioned. Here in Wa. we seem to REALLY suffer from corrosion issues due to the wetter weather and humidity, and the only solutions I have found are to replace all of those harnesses and connectors with brand new, upgraded shielded connectors from Z1 and similar sources. Avoid low-cost and buy upgraded ONLY, and even a so-called working/cleaned IACV is apparently no good- new replacement only has worked for me, I tried both old and new replacement.
BTW, do you use Doug Smith at Fairlady Motors for your work? I heavily recommend him as he and Eric WILL solve your Z32 problems and with the least hassle and cost, and provide knowledge and service better than any other in the area that I know of.
Good Luck, and talk to Doug!

[dominicnwusa]

Hey Dcaff!

I was wondering if I was going to see a reply from you! I actually was able to pull off of I5 luckily, and into a rotorooter parking lot (wonder if thats some sort of sign haha). Just past the Boeing airfield outside of Seattle.

Yeah just tinkering around with the Z every weekend I find new terminals to clean and replace. Luckily enough my Z didn't have and really bad corrosion with the exception of the CTS which looked like a science experiment gone wrong. I'm actually up North in the Mill Creek area so I have been using Z Sport automotive in Everett. Seems like an OK shop but due to a few issues I think I'll stop using them. One of my throttle bodies was dented after the 120K service, as if something heavy was dropped on it. so it went from having a nice rounded "O" to having a flat spot that caused the throttle plate to stick. They then tried to tell me it came in that way. Pretty sure I'd remember having to kick the gas pedal every time i take off from first. Then during the clutch job they failed to install the upgraded clutch fork and didn't bother to tell me. I found out by finding it in the box of old parts they gave back to me. It was freshly greased up and looked ready for install, I guess they couldn't get it to work or forgot. After that I think i'm pretty much done with them. Other than that they were incredibly friendly and had great turn around time.

Right now its at Gregs japanese auto in Tukwila. I know they aren't a specialized Z shop but it was the only good option within my 5 mile towing radius. I've heard of fairlady motors but Tacoma is usually quite the haul for me. Thank you for the recommendation, If i'm able to get the z back in decent running shape I'll have to get down there and have them take a look!

[dominicnwusa]

Update from the shop:

They are telling my my ECU is done for. He said they hooked up all their computers to the car and the Z won't communicate with them. I reminded him that the car is OBD1 and the only computer that would talk with it is a conzult. At that point he said yeah thats what we have and its not working. Said he has a guy down in Denver who will rebuild the ECU for 650 dollars since they don't make them anymore. My only other option is for the shop to go on an international search for an ECU. Haha too funny, clearly he must not think i have a decent understanding of my car. Z1 has used non turbo ECUs for 200 bucks.

I asked them if they did a compression test since he was saying the head gasket was blown the last call i had with him. He said no because today it was blowing black smoke out and that gave him enough reason to skip a compression test.

I definitely wouldn't rule out a bad ECU since i have a leak (water leak) from what i think is the AC drain line. it was decently wet when I pulled out the panel from the foot well. He's waiting on my response on what I want to do. Thoughts?

[nissanfreak12]

Im sure you can ask and there will be many people that have ECU's for sale. I have a 91 NA 5 speed sitting the garage I can let go for 75 plus shipping. Ill plug it in to my car to make sure it works first.

I really think you need to look back into the CTS. That could cause black smoke as well. I think you need to get it out of that shop. Dcaff may now someone in that area that he would trust to look into your car. He says he has a guy down in denver that will rebuild, the only one I know that lives here that knows anything about these cars is Tim(Woody75 off TT.net), but I don't think he rebuilds ecu's.

Check out conceptzperformance.com or even specialty Z. I prefer either over Z1 just for customer service. I have also dealt with Coz for many years, good guy always willing to help.

[dominicnwusa]

I would have loved to buy your spare off you, but i have already sourced another one before I read your post. I appreciate that though! Regardless of how this turns out I plan on putting an OEM CTS in and a proper splice just for my peace of mind.

I need to clean out my Evap box too from the look/sound of it. I bet what happened was water dripped on my ecu on my way to the airport as I had the AC running on full blast. Doing some forum searching another guy who had a busted ecu had the SAME exact bucking, sputtering, and smokey exhaust I did when I was moving it around the rotorooter parking lot. who knows maybe the new ECU will clear up the vibration I originally started this post over.

I definitely plan on getting it out of the shop first chance I get. They either don't know a whole lot about z32s, are trying to bend me over for as much cash as possible or both.

[dominicnwusa]

Ok updates!

Got the ECU down to the shop where they proceeded to have me wait for 3 hours without even so much as touching the car. The front office guy came and told me they wouldn't be able to get to my car back to me until Monday, to which I responded I'm taking my car and leaving. changing out the ecu is literally 4 screws and a plug and it was complete nonsense to have me wait 3 hours and then tell me it wont be done until Monday. He assured me that it was MUCH more than just 4 bolts and a plug which really sealed the deal on me making sure I got my property out of that shady shop. Luckily they zeroed out my work order so it didn't actually cost me anything which was a relief.

Drove my car down the road to the mall, went into sears, got myself some basic tools and swapped out my ecu in the parking lot. Car running as good as new! well, my lumpy idle is still present but hey, it felt good to drive home finally.

I noticed when I pulled codes (55) and then turned off diagnostic mode, which if i remember right puts the car into learning mode, My idle sat perfectly at 750 RPM but then after a bit it chose to sit back at 1k where it had liked to before. Wondering if perhaps a sensor or something isn't adjusted right....

Today I have a lot of work to do on the car. Brake/rotor job, intake piping, leak test, some harness replacement... I'll be back in touch later today

[dominicnwusa]

Ok, I think I found what is causing my idle issue. I used a boost leak plug tester and was able to trace a vacuum leak to the back passenger side of the engine. Wasn't able to source which line was leaking but I'm assuming its an EGR line. didn't want to do a plenum pull but that looks like the best way to tackle it.

Found a leaking fuel line while I was poking around too.

[DCaff300ZX]

Sorry I missed out on your earlier responses, glad you got away from the shysters. I've had similar experiences with otherwise reputable shops and my Z32 before taking on my own Z work, with the help of Doug at Fairlady for more major work and insight/knowledge. DO contact Doug and plan on using him for any needs you can't handle, and for insights into testing and what's important and what's not so important- invaluable stuff for knowing what you are doing and being confident in your results. Doug is the ONLY NW Z32 source I trust, period...one of about 3 people total in the world outside of family that I trust completely.
Good luck, and enjoy your Z!

[RubyRed300ZX]

There's a 4" long vacuum line that runs from the EGR valve to the backside of the plenum on the passenger side. It's formed almost into an "S" curve. A bytch to get to as it's next to the firewall and down deep. But, it can be done with some unusual tools or a lot of luck using the Braille method.

[dominicnwusa]

Hey guys!

Thanks for the responses. I did manage to replace the vacuum line going to the EGR itself after much frustration with it haha, but its done. I ran a line directly from the EGR to the solenoid, bypassing all the piping in between. This definitely cleaned up my idle a little bit, however I still have that leak when I (attempt) to pressurize the intake.

I used a paper towel tube to try and isolate the hiss to a specific spot, but im not too confident on if its coming from the IACV assembly, the EGR valve, or even quite possibly the rear PCV hose. You'd think it'd be easy to source but, nope....

So I ordered the PCV hoses as those are all original and need to be updated, the two remaining hoses to the IACV assembly (regulator-balance tube, and supply hose going to the accordion pipe) as I've already replaced the inner two hoses in the middle. Also grabbed new brake booster hoses because why not, it'll look better.

I do have the EGR delete kit, but im very hesitant on removing it due to the fact that I don't have a wrench big enough to fit the bolt attached to the exhaust bung, and because I would have to do the pipe cut method. also Im not entirely sure its bad. If my EGR is to blame its only mildly failing as I can push up on the diaphragm while the car is idling and boy does it try and die when it starts breathing exhaust fumes. Would the valve be making a hiss when pressurized?

Next up I took a look at that leak under my dash. I thought it was the EVAP drain hose. Nope. My leak is coming from between the evap box and the heater core box. Its leaking water for sure. Not really sure how to tackle that one without having to remove my entire Dash. as a band aide I have a tub of rocks that absorbs moisture in the air sitting under my dash next to the ecu and i leave the carpets pulled back to keep mold/moisture at bay.

I'm also wondering if this leaking issue can be related to the fact that I only get HOT air out of my footwell vents. Any guidance or help troubleshooting fixing my under dash leak would be greatly appreciated. I've checked out the FSM and have a general idea of how the HVAC system works but still don't know where to start. I am not entirely keen on discharging the AC as its still R12 and pumps nice cold air after all these years.

You guys have been great helping me out this far! No words can express my gratitude!

[DCaff300ZX]

Glad to hear we have helped!
Water Leak- Unfortunately, more bad news...the leak is most likely the heater core (and possibly a corroded inlet hardpipe, but far less possible) and while doable in the car and with no dash removal, is a TOTAL PITA and probably less doable for anyone larger than Japanese-sized as fortunately I am. A short term solution to the leak is to loop the heater core inlets in the engine bay with a piece of longer hose, but then no heat and don't use the climate control at all until core replaced- and no need to mess with dumping the system/replacing with updated at any point in the repair. BTW, a cooling system pressure test should be able to prove that the core is leaking or not- do that before considering any work here.
You can get a new heater core at any Z source, you go in and surgically cut out the old one and hose connect in the new one after cutting the new inlets to fit...I have a how-to I could help you with and did it myself in two days on my NA that went the same route as yours has in numerous ways- I had three 30-60 minute passes at it (all my body could handle upside down in the drivers' well, legs/feet up the seat which is all the way back) each day, done and refilled/working the final day- LONG tough weekend but necessary as it was my daily at the time. But easily the worst Z32 job possible other than testing turbos/boost leak testing on my TT. If you click on my build link in my sig, and go to the point where I am boost testing it may give you some help and insights.

Hiss- possibly and probably an engine seal leak such as a valve cover (common) or rear main seal. Any worn seal will leak pressurized air as I found boost leak testing, and WILL provide projects to fix them all (or frustrate you!) as you hunt around...not a bad thing long term, except for not fixing the current problem. There are quite a few possible boost leak sources even on an NA such as injector o-rings and more, so hopefully the fsm can help you in that hunt...you need to suspect any engine seal to the crankcase and even the intake plenum at ALL points such as balance tube o-rings (commonly bad all smushed in that hot space) and pcv, etc., etc., etc.

EGR- Probably not the issue, and I kept mine at Doug's advise (emissions) since it is OK and I replaced the harness with upgraded. If removing for aesthetics/weight/bad OK, but otherwise not worth the hassle and doesn't harm performance at all.

Hoses- Replace them all that you can find and reach/remove, they all will need it soon enough so go with peace of mind and another potential issue gone. Same with sensor connectors especially injectors, IACV, PTU, and CTS both. Others can wait for breaking when removed (brittle old plastic) if not an issue otherwise. BTW, avoid cheap silicone hoses for any boost or higher than normal heat applications (turbo, oil), be sure any silicone hoses aren't chinese crap (good silicone still costs less than OEM rubber) and you're OK. Any silicone is OK for vacuum/lighter duty.
FYI, I've been advised by Doug to not buy silicone at Z1 or Concept Z, the issue being whether or not they are a properly wound/layered hose (more expensive but hold boost, water/oil properly) or not (cheap chinese)...not sure of a reliable source, maybe someone else is? SPZ maybe?

Good Luck, and I'll keep an eye out for more questions and BTW, enough problems here to be beyond normal DIY and worth a trip, or call at least to Doug at Fairlady, IMHO...