Problems setting base idle

[robomatic12]

I'm trying to chase down a random misfire/pop at idle and came across something strange with the IAA. My z has never had a problem idling at the correct rpm, about 750rpm. But if I unplug the AAC connector (yellow one), the idle does not change. The base idle screw is screwed all the way in tight. I have read the engine should stall if it is turned all the way in.

I checked timing to be at 15*, the TPS was replaced about half a year ago and set to the correct voltage, the throttle bodies are clean, engine only has 10,000kms on it since rebuild, new injector connectors and new coil pack connectors. No codes on ECU, o2 sensors pass the blink test.

I did a boost leak the other day found one hose clamp loose on an accordian pipe, found a torn vacuum line to BOV and found that the BOV's would whisper a little air out at 5psi. Fixed those and then I could not hear anything else, I'm going to tape up the BOV's and see if I can hear anything else leaking.

I took off the air regulator today because I thought it might have been faulty but I cleaned it, checked for proper solenoid operation and ohms. It's working normally. I didn't want to remove the IAA without a new gasket so I sprayed some cleaner into it with the engine running.

Is there something else other than a faulty IAA I should be looking for? More vacuum leaks?

[marty1mc]

Have you cleaned all your injector, coil packs, CAS, etc.. connectors?

[GerryO]

Hopefully you'll be able to isolate the random miss problem to one faulty plug/coilpack/injector/harness wire/connector/cylinder.

Idle speed is controlled by the ECM switching the AAC ON and OFF very fast, unless the idle adjustment screw has been set too high all along, which I'm guessing could over time result in things getting stuck in one open position.

A properly working and connected AAC (plus TPS, Air Regulator, Temperature Sensors, MAF and everything else that determines idle speed) enables idle speed adjustment above the ECM determined lower limit, but not below.

http://home.swipnet.se/e-solutions/IdleTech.html

A dirty MAF on my F-150 caused very subtle missing at all shift points and random violent bucking at freeway cruising speeds. Vacuum leaks involve air volumes entering the intake system that are not measured by the MAF and correctly communicated to the ECM.

[robomatic12]

Marty- I've cleaned everything besides the injector connectors as they were replaced last year but I'm going to go back through them incase some corrosion has formed. I know they wern't packed with die-electric grease, but I've been doing it on every connector since.

Gerry- I've tried the routine pull a coil pack connector to see if any cylinder does not drop or drop as much as the others but cannot pinpoint it as they all seem the same. I'm going to ohm all of the injectors while cleaning them and greasing. Is there any way a conzult or similar program would help me diag an idle misfire?

So am I understanding wrong that I should not be able to mechanically drop the idle below factory specs? With the aac connectors off. Because right now with the connectors off it will idle around 700rpm and that is with the screw turned all the way in.

I know one of my bov's has a small leak when pressurized at 5psi with a leak detector. Would this be enough to upset the idle? I'm going to try and get ahold of stock recirc valves to test it out.

[GerryO]

Marty- I've cleaned everything besides the injector connectors as they were replaced last year but I'm going to go back through them incase some corrosion has formed. I know they wern't packed with die-electric grease, but I've been doing it on every connector since.

Gerry- I've tried the routine pull a coil pack connector to see if any cylinder does not drop or drop as much as the others but cannot pinpoint it as they all seem the same. I'm going to ohm all of the injectors while cleaning them and greasing. Is there any way a conzult or similar program would help me diag an idle misfire?

So am I understanding wrong that I should not be able to mechanically drop the idle below factory specs? With the aac connectors off. Because right now with the connectors off it will idle around 700rpm and that is with the screw turned all the way in.

I know one of my bov's has a small leak when pressurized at 5psi with a leak detector. Would this be enough to upset the idle? I'm going to try and get ahold of stock recirc valves to test it out.

Ohm checking the injectors is a good idea and maybe there's an electrical test for coilpacks too. A failing injector of mine worked intermitently for a while, before it failed completely.

Imagine you could move a timing light from one cylinder to another, watching each one for a while and noting any misses/inconsistencies. Suppose you could also video tape timing light firing patterns for each cylinder.

Have an old Heathkit engine analyzer that displays the spark pattern for each cylinder, but it's also based on a single ignition coil for all cylinders. The Consults run a power balance test that purposefully executes a pattern of not firing all cylinders one at a time and in a specific order, but I'm not sure how much information that would provide.

obd-scan-tech-nissan-power-balance-works-t504532.html

Are you able to increase the idle speed using the adjustment screw? Manual adjustment is on the low side is sort of a fail-safe in the event that the ECM input is lost and on the high-side, it should be just slightly lower than the ECM controlled speed. It almost sounds like AAC/IAC internal workings aren't moving.

The temperature sensitive Air Regulator increases idle speed, until the engine is fully warmed up.

[robomatic12]

The idle speed will increase if I screw the adjustment screw counter clockwise. I first realized this when I went the wrong way and ended up with the base idle at around 1,100rpms. Then when I turned it all the way clockwise until it stops, it is at around 700rpm.

Whenever I turn on the A/C the fast idle will turn on and off properly. So that solenoid is working okay.

I notice when I first plug the AAC connector back on, the idle will bump up quite a lot and then settle down to around 750rpms after 5-10 seconds.

[GerryO]

http://www.kroffts.com/kke/files/Nissan ... Manual.pdf

[dudewtf]

Unplug your maf senso, turn your car on, chek engine light will turn on, see if the missfire continues. If it continues check your sparks.

The car should hold an idle with the maf unplugged.

Also whag kind/brank of sparks are you using???

And did you say you did a balance test on all coils and your isle didn't change?

[robomatic12]

I'll try the MAF sensor test tomorrow.

I'm using the NGK IX plugs with the 6 heat range I believe, they are the plugs that SpecialtyZ sells.

All of the cylinders drop the idle when unplugged one at a time, I cannot pick out one that drops more than others either. I'm going to try and get ahold of a computer program like the one Gerry linked too the manual for.

[dudewtf]

s*** sorry for all the typos

if you had a bad coil the idle wouldnt change when unplugged. so all your coils are good.

maybe you just have a faulty injector? let us know about the maf test

[marty1mc]

Here is a link to a very good site on idle. I don't know if you have seen it or not since it gets pasted a lot on different sites. But, it's well worth reading and working the steps...

http://home.swipnet.se/e-solutions/IdleTech.html

http://home.swipnet.se/e-solutions/IdleTech2.html

[robomatic12]

I tried unplugging the MAF, the idle stumble/misfire was still there so I guess that eliminates the MAF.

I cleaned the injector connectors and pins themselves and they all ohm correctly at 12-13ohms.

I checked the coil packs to be at 1ohm, factory spec is around 0.7ohm but I think my multi-meter does not go down accurately enough, the moment it reads it goes from 0.6 up to 1.0 ohm. It seems others have similar readings online. So they should be okay.

I did another boost leak test today, there are for sure no other leaks besides the passenger side BOV. Still trying to get my hands on a pair of factory recirc valves.

I'm also ordering silicone idle air hoses and the gasket so I can pull the IACV unit off and clean it. I'll let you guys know how this works out.

[GerryO]

It sure would be nice to know if the miss is completely random or always associated with one specific cylinder. Listening closely to the exhaust at the tailpipe, tells me the most about how smoothly an engine is idling, unless a miss is very obvious. How many miles on the engine, plugs, injectors, PCV valves, EGR tubes, etc?

The supply of intake air should be most universal to all cylinders, so things should still come down to a weak or intermittent supply of fuel or spark to one or more cylinders.

First started my engine up after changing the water pump/timing belt/front oil seals/etc, with the plastic intake ducting and MAF off of the car. After running a fairly short time, the engine sputtered and died.

The dirty MAF on my F-150 was causing things to lean out too much when I slightly let up on the gas pedal.

[robomatic12]

The miss seems to be completely random, its every 10-15 seconds I can hear a little stumble/pop. I can't pinpoint it to left or right exhaust side, also being that they are connected together further up ahead. The engine idles smooth, you can't feel any vibration inside or see any rpm fluctuation. Neither does the engine shake. It's only an audible thing.

Engine has 8,000kms on a rebuild, plugs and pcv valves were replaced at that time. Injectors look original so 152,000kms. Deleted egr.

I cleaned the maf with maf sensor cleaner a couple weeks ago. I noticed when I had the engine running then unplugged MAF it died. I restarted and it chugged to get going but ran with a high idle. Then I plugged it back in with the engine running almost died but caught itself and idled normally back at 750rpm. The random misfire continued throughout.

It almost seems to me that sometimes it's gone and then reappears. Definetely very random and not on one cylinder atleast that I'm aware of. Any ideas how to narrow it down? I'm guessing I really need to get my hands on nissan consult.

[GerryO]

Some interesting reading here, particularly about issues specific to earlier model years, plus the TPS, CAS and PTU.

http://www.xenonz32.com/basicterms.html#2+2%20/

Is the miss any better or worse when the engine is cold or full warmed up?

[robomatic12]

While the engine is warming up, having a higher idle... I cannot hear any misfire. It's only apparently when fully warmed up and the idle has dropped down.

I've done a little bit of searching around on twinturbo.net and there are some posts saying that due to the lowered spark gap at 0.035 instead of 0.044 stock there is a normal odd pop noise at idle. Apparently normal unless the engine is shaking? Does this make sense?

Obviously that would clear up at higher rpms which is why we lower the spark gap on modded engines with higher boost.

** I have the series 2 ptu, and checked the cas for the worn dowel due to misalignment, appears normal. I replaced the TPS with oem and adjusted it to .44volts last year when it started getting dead spots.

[GerryO]

While the engine is warming up, having a higher idle... I cannot hear any misfire. It's only apparently when fully warmed up and the idle has dropped down.

I've done a little bit of searching around on twinturbo.net and there are some posts saying that due to the lowered spark gap at 0.035 instead of 0.044 stock there is a normal odd pop noise at idle. Apparently normal unless the engine is shaking? Does this make sense?

Figure at idle the air/fuel mixture is leaner, after the engine is fully warmed up, and that the spark jumping the narrower gap is always comparitively weaker.

http://en.wikipedia.org/wiki/Spark_plug

The gap adjustment can be fairly critical, and if it is maladjusted the engine may run badly, or not at all. A narrow gap may give too small and weak a spark to effectively ignite the fuel-air mixture, while a gap that is too wide might prevent a spark from firing at all. Either way, a spark which only intermittently fails to ignite the fuel-air mixture may not be noticeable directly, but will show up as a reduction in the engine's power and fuel efficiency. The main issues with spark plug gaps are:

* narrow-gap risk: spark might be too weak/small to ignite fuel;
* narrow-gap benefit: plug always fires on each cycle;
* wide-gap risk: plug might not fire, or miss at high speeds;
* wide-gap benefit: spark is strong for a clean burn.

A properly gapped plug will be wide enough to burn hot, but not so wide that it skips or misses at high speeds, causing that cylinder to drag, or the engine to begin to rattle.

As a plug ages, and the metal of both the tip and hook erode, the gap will tend to widen; therefore experienced mechanics often set the gap on new plugs at the engine manufacturer's minimum recommended gap, rather than in the middle of the specified acceptable range, to ensure longer life between plug changes. On the other hand, since a larger gap gives a "hotter" or "fatter" spark and more reliable ignition of the fuel-air mixture, and since a new plug with sharp edges on the central electrode will spark more reliably than an older, eroded plug, experienced mechanics also realize that the maximum gap specified by the engine manufacturer is the largest which will spark reliably even with old plugs and will in fact be a bit narrower than necessary to ensure sparking with new plugs; therefore, it is possible to set the plugs to an extremely wide gap for more reliable ignition in high performance applications, at the cost of having to replace or re-gap the plugs more frequently, as soon as the tip begins to erode.
-----------------------------------------------------------------------------------------------
Other notes say that narrower gapped plugs wear faster and that wider (to a point) gapped plugs more reliably ignite leaner air/fuel mixtures.

[robomatic12]

So by the sounds of that article it sounds like I may be encountering the downsides/risks of gapping plugs down to prevent spark blow-out by raised boost levels. I guess it's worth a shot to try gapping the plugs at the stock gap to see if the idle improves. At the same time, I would rather have a odd pop at idle rather misfiring at high rpm/boost.

I'm still also curious to see how the leaking blow off valve (albeit minor) would effect things. If it leaks air past the piston inside when pressurized to 5psi, I'm guessing the engine vacuum might be sucking air back through it? Further leaning out the mixture at below-boost pressure.

I really appreciate the continued help Gerry!

[robomatic12]

So my parts finally came in today. I pulled off the iacv/aac unit, cleaned all the ports out and thoroughly cleaned the connectors. Then I replaced the air regulator, ficd and aac connectors, they were broken and showed signs of corrosion.

I was able to get my base idle to drop down to 700rpm in order to follow the idle procedure, which jumps up to 750rpm upon connecting the aac.

There is still the same stumble/misfire at idle though....

[Ace2cool]

I'd like some more information on this mystery misfire as well. Sounds about like what's going on with my TT. A random "pop" every 15 or so seconds, just audible enough for me to notice. Never had anyone else comment on it. No change or drop in idle, no shaking, nothing of the sort. No ECU codes. No clue what it could be. I've looked at everything I can think of.

Maybe running rich and igniting fuel in the precats when there is a buildup? I dunno, just spitballing at this point. I think I may pull my O2 sensors and see how they look and ohm them out.

[robomatic12]

That sounds pretty much exactly what mine does, it just pops every so often...most people don't notice it until I point it out or it's a trained mechanic who is talking to me at work while it's running will hear it.

I don't have precats, nor do I have cat converters. The O2 sensors were one of my last things to check out just like you, perhaps I might put a new pair in.

What plugs/plug gap are you running ace?

[Ace2cool]

Stock NGK plugs with .42<-? gap. Might be mistaken on the gap, but the plugs are brand freakin new. Less than 1,500 miles on them. Check the EF section; there's a section for testing the individual components of the fuel control system, and I believe the O2 sensors have an Ohm reading. I'm gonna see if I can't test mine this weekend when I get time to breathe.

[robomatic12]

Yeah I'll see what they test out at on the weekend also. I'm running the ngk IX plugs, heat range 6 with a 0.35 gap, but I have about 10,000kms on them. I don't think they should be dead already... :/

[robomatic12]

I think I may have found the solution, I re-did my O2 sensor test again today. Last time I did it was probably 4-5 months ago and both were fine. The right side O2 sensor blinks satisfy the 5 blinks in 10 seconds, but the left side sensor does not blink at all.

I ohm'd the two outer terminals off the sensor connector and got a reading of 10ohms on the right (working) side and my DMM showed nothing (infinite/open I believe) for the left side. Both harness side connectors have +12v with engine running and show a reading of 50ohms from the ground terminal to the negative battery terminal.

To me this sounds like the left side O2 sensor heater element has died and the sensor is not giving any info to the ecu, or telling it that the engine is constantly rich. Do I need to replace the 02 sensors, or correct a rich condition?

[Ace2cool]

Well, replacing the O2 sensors will correct the rich condition, theoretically. As long as everything else is functioning properly, at least. Going to go check mine today.

[robomatic12]

So apparently I made a mistake switching between the left and right o2 sensor while the engine is on during mode 2. I was not turning the mode knob in the correct sequence. Both o2 sensors are working okay, but the left side had a broken heater element which is why it failed the ohm test from service manual. I replaced the left one any ways with the Bosch #13901 just in case that was effecting things.

It's hard to say from the shorter drive I had today, but I believe there is still a misfire at idle.