Idle Misfire & Cruising Stutter

[cbh148]

Nearly 800 miles on rebuilt ca18det.
Brand new Bosch o2 Sensor (part #13276.
Brand new water temp sensor (the one for the ECU with the injector-style plug, not the one for the gauge).
Walbro 255
Nismo fuel pressure regulator set to ~37 psi (seems like sometimes it's 35, sometimes it's 40)
New gaskets nearly everywhere (don't know about the intake manifold, but valve covers are fine)
Cat-delete (sounds like it may be leaking)
Smells rich at idle, but fuel mileage seems OK.

As posted in my other thread, I don't currently have any idle control or cold start gizmos. When I start it up cold, it wants to die pretty bad until it warms up. From there, it's a bit better. Most of the time when I'm driving, the idle tries to drop really low (~500 rpm's or lower) so I'm always having to rev it or rest my foot slightly on the gas at red lights. However, sometimes when I come to a red light, the idle stays up high around 1700 rpm's. I tried raising the idle with the throttle body screws and using the throttle cable nuts too, but I'm just chasing the idle around. I can't seem to get it to consistently stay around 1000 rpm's, but if I'm having an on/off misfire at idle, I'm guessing it's pointless to try and set the idle because that misfire is messing it up, right?

Also, when driving down the road, it stutters a bit when I'm cruising in gear (generally maintaining a constant speed).

I just tried unplugging the o2 sensor to see if it made a difference, and it didn't.

I've got an extra set of coil packs and another coil loom. I'm thinking I'll check my plugs, gap them to 0.8, and run the other set of coil packs to see what happens. I probably should make a boost leak tester and see if I'm leaking anywhere. Something else that just crossed my mind, I set my TPS awhile back, but I remember it being weird because I couldn't get it to reach both values for off throttle and wide-open.

Any advice would be greatly appreciated!

[float_6969]

sounds like boost leak to me

[cbh148]

sounds like boost leak to me

Think so? I'm gonna make a boost leak tester today. Wouldn't that also reveal vacuum leaks around the intake manifold, like intake manifold gaskets and hoses??

And I forgot to mention -- when I get on it, it doesn't stutter. It accelerates smooth at wide-open or near wide-open throttle. It's not incredibly fast, but this is my first ca18 and I'm not sure how quick it's supposed to be, especially at 6-7 psi on the t28.

Yesterday, I pulled all the plugs. They looked really clean. No oil, no ash, almost brand new looking. The gaps were a bit off, but nothing higher than 1.4 mm. I set them all to .7 and it made no difference.

I stopped by Tim's house the other day and he thinks the idle (which kinda sounds like I have big cams lol ) is a normal ca18 thing.

[r34 gtr]

I would get that air idle stuff on there and hook up a line to that thing coming off the cold pipe. If there is a leak its probably there, as I am unsure of the ability of rubber baton end caps and duct tape to seal intercooler pipes. Haha. Everything sounded great minus the idle hunting a bit, which is to be expected with all that stuff missing and the stock ecu. Don't worry so much!

Oh and I forgot to mention, but there are a bunch of horrible little vacuum nipples on the bottom of the throttle body that can cause a poor idle if they are not capped correctly. They are hard to cap correctly. I think I might have done something to mine like cut them off, tap the hole, insert bolt, melt bolt into hole with eye lasers, cover remains in rtv, and then encase the whole thing in frozen carbonite. Seriously those little vacuum nipple things are the worst.

[cbh148]

I would get that air idle stuff on there and hook up a line to that thing coming off the cold pipe. If there is a leak its probably there, as I am unsure of the ability of rubber baton end caps and duct tape to seal intercooler pipes. Haha. Everything sounded great minus the idle hunting a bit, which is to be expected with all that stuff missing and the stock ecu. Don't worry so much!

Oh and I forgot to mention, but there are a bunch of horrible little vacuum nipples on the bottom of the throttle body that can cause a poor idle if they are not capped correctly. They are hard to cap correctly. I think I might have done something to mine like cut them off, tap the hole, insert bolt, melt bolt into hole with eye lasers, cover remains in rtv, and then encase the whole thing in frozen carbonite. Seriously those little vacuum nipple things are the worst.

LMAO!!!

Well I made a boost leak tester today, and gawddang at the boost leaks I had. I fixed them all yet it made no difference for the idle misfire and the stutter at cruising speeds. Just made my BOV a bit louder. Honestly, it doesn't feel any quicker. Worth mentioning, I charged the turbo and intercooler piping AND all through the intake manifold -- in other words, I didn't cap off the i/c piping before the throttle body. I could get the gauge to read about 5 psi of pressure, but there was a pinhole leak on the weld for that tube on the i/c pipe right before the throttle body (the one that's capped off for now until I can put idle control on). So, I went to a friends and had him zap it with a welder.

I couldn't find any air leaking out around my intake manifold at all. Not under the throttle body, not in the area where idle control is supposed to be, not around the FPR or butterly valve vacuum lines, nothing.

Questions:

Could my MAF be bad? It's a stock CA18DET MAF as far as I know. However, since it doesn't stutter when I romp on it, would that rule out a bad MAF?

Maybe a coilpack on its way out? But once again, it doesn't stutter at all when I hammer down on the throttle.

Could changing my ECU out help? I've got another stock ca18det ecu, so I might swap it in tomorrow just to put my mind at ease.

Thanks for the help guys!! Bout to turn over the 1000 mile mark on this rebuilt CA tomorrow!

[float_6969]

If it was ignition related, the issue would show up under load, not under idle/part throttle, so you can rule that out all together. As Tim said, if you're running the stock ECU w/o any idle control hardware, it's probably not going to idle very well. Also, if your TPS isn't reading idle, that may be causing idle issues as well, as the ECU controls the motor a bit differently at idle.

You could try cleaning the MAFS as that may be causing issues as well.

Have you tried pulling the codes to see if it brings anything up?

Also, it sounds like you're wiring might be a bit shoddy. If someone has messed with the sheilding for the wires for the MAFS, CAS, or O2 Sensor, you could be getting a poor signal to the ECU, which could cause all kinds of problems.

[cbh148]

If it was ignition related, the issue would show up under load, not under idle/part throttle, so you can rule that out all together. As Tim said, if you're running the stock ECU w/o any idle control hardware, it's probably not going to idle very well. Also, if your TPS isn't reading idle, that may be causing idle issues as well, as the ECU controls the motor a bit differently at idle.

How do you guys set TPS's on your ca18's? I'm going to reset mine, but I know the FSM wants you to check the resistance with the TPS unplugged or something, and I'm seeing where a lot of people check the voltage with the TPS plugged in (and the key on, I assume). Heck, I'm also seeing where some people adjust the TPS till idle raises then back it down a hair.

You could try cleaning the MAFS as that may be causing issues as well.

Probably going to try that today. I'll just use the generic AutoZone MAF cleaner spray stuff.

Have you tried pulling the codes to see if it brings anything up?

I haven't done this. I'm not familiar with how to check for this on the CA but it can't be that complicated right?

Also, it sounds like you're wiring might be a bit shoddy. If someone has messed with the sheilding for the wires for the MAFS, CAS, or O2 Sensor, you could be getting a poor signal to the ECU, which could cause all kinds of problems.

On that subject -- the way may harness is now (after my friend "cleaned it up") has my MAF wiring run along all the injector/TPS/CAS/water temp wires. It goes past the CAS and over to the MAF, rather than the factory route, which I assume is has the MAF wiring routed along the perimeter of the engine bay (like a KA) and not laying next to hardly any other wires.

In about a week, my second harness should be ready to swap in. This harness has all the plugs for idle control stuff, so that will be fantastic. I'm hoping that smooths out the idle altogether and maybe makes the highway stutter stop too (if none of this other stuff does).

[cbh148]

Double Post!

Just realized I never mentioned that I have a KA throttle body (not sure if it's from a SOHC or DOHC). The TPS on it only has one plug (on wires). I see that my extra ca18det manifold has a TPS with 2 plugs on it (one is on wires, the other is directly on the black TPS box). Surely this isn't an issue right? I want to say that the plug on the TPS box is for automatic transmission only.

[float_6969]

See the FSM for adjusting the TPS.

Yea, nothing special on the MAFS cleaner.

See the FSM for pulling the codes and what they mean.

The 2 plugs is normal. The Automatic uses the plug on the TPS itself. The plug on the wires is the actual TPS plug.

[TheMAN]

you should use brake cleaner to look for vacuum leaks too... spray at gasket areas and where hoses attach... if idle changes, there's the leak!

[float_6969]

That doesn't work very well on anything that is infront of the TB.

[cbh148]

I think I may have made 2 steps forward and 2 steps back today...

I just swapped out my engine harness so I could have all the plugs for idle control and cold start. I put all the idle control valves and stuff on as well. I used another AAC valve that Tim gave me (since mine has the spring fiasco going on), but he said he didn't think it worked. It had all the springs and stuff on it from what I could see, unlike mine.

One of my problems was setting the idle. I had tried to rig the idle up with the throttle body stopper screw AND adjusting the cable bracket nuts before I got my idle control stuff, so I undid those things to let the throttle close all the way (is this the right method?) so that the AAC could take care of idle. I tried to adjust idle then with the idle screw on the FICD body, but it didn't seem to work.

I tested the voltage on the wiring plugs for the AAC and cold start valve. The AAC plug had about 6 volts going to it at idle, then jumped up to almost 13 volts when I'd rev it. The cold start plug had a constant 12v going to it. Is this right? Also, I unplugged the idle control while it was running and it didn't seem to make a change in idle. Not to mention, it still kinda feels like I have to give it some throttle to start the engine up cold, so maybe my cold start isn't working as well.

My current harness doesn't have a knock sensor, and the knock sensor wiring is not ohm'd out, so I figure it's the equivalent to me just not having my knock sensor plugged in -- which would mean my ECU is in safe mode right? It feels slower than normal, and especially when I'm crusing and I add a little throttle to accelerate, it seems to dislike going into any boost.

I'm going to see what I can do about getting my knock sensor situation figured out tomorrow. Also, I'm going to address my vacuum situation a bit -- the previous owner had the BOV vacuum line and the wastegate vacuum line run to the intake plenum (he put nipples on the holes where the idle control was supposed to be, which I removed when I put that stuff back on today). I'd like to have my wastegate line MUCH closer to the turbo, and I don't want to have my BOV go into the vacuum line for the FPR and butterfly valves (which I'm also using for my boost gauge. I assume this is OK).

I also cleaned my MAF today and fixed a random oil leak that started through the middle of my oil pressure sending unit (not the threads, but through the middle. WTF. Replaced the darn thing.)

So all in all, I think my cruising stutter may have gone away. I'm hoping that not having a knock sensor and/or having my TPS and throttlebody set wrong is causing my idle and power to be fudged up, because that's about to be fixed.

Does anybody know where I can get another AAC idle control? Does a KA or fwd SR idle control work?? What about the cold start valve? I have a friend with an extra RB20 cold start, and it looks damn near identical.

As always, thanks doods!!