Thread: Help with misfiring W10 92 SE-R. Won't idle, misfires 24/7

I have a turbo 92 SE-R. Has a W10 Avenir and stock t25. Running 370s at 4 bar, N60 maf, and I recently got a used Calum RT v1. The car has been misfiring and runnning altogether crappy. It threw Code 34 which is the knock sensor, so I tested the circuit and sensor for continuity and both tested fine. Cleaned and replaced the knock sensor and it still runs like crap. I start fiddling with the Snap-On Modis we have at school and start reading live data while the car is running. I noticed the IAC/AAC valve was 95-100 percent open whether it's cold or at operating temperature. So while the car is running I went into the "Actuator Tests" on the Modis and completely shut the IAC/AAC while the car was at operating temperature. This completely fixed my problem. Stopped misfiring, gained throttle response, smooth idle, 19 in/Hg vacuum. Ran great! So my question is what exactly does the IAC and AAC do? How do they work together to determine anything? What does this diagnosis tell me? I want to know what I fixed by closing the IAC/AAC and what I need to do to permanently fix my problem.

I'm not too clear on what it does, but I know they can get a bunch of carbon buildup in them, causing them not to work properly. Pull it off (not easy to get to), clean it out with your choice of cleaner (I think I used carb cleaner, but double check that), carefully scrape off the old gasket from both sides, put a new paper gasket on, and put the IAC back on (not easy).

Don't be like me and do it half-assed the first time and have to pull it off again because too much of the old gasket was still on the engine side, causing it not to seal and therefore leak. From what I've heard, they almost always work after cleaning (unusual to have it malfunction and need replacing). It didn't solve my issues, because my issues were not caused by it. But now that it is clean I can drive at a crawl and the car won't buck.

They're quite easy to get to when you delete power steering and A/C. I'll pull it off and clean it in the parts washer or with brake cleaner, but I kinda don't think that's all my problems. I really wanna know how it's supposed to work.

So I grabbed my spare AAC (on side of intake mani next to oil filter) and cleaned the hell out of it and put it on my car. Also swapped the air regulator (black box under intake mani) for a different one I had laying around, and the same problem still exists. Any suggestions on what to try? I'm up for anything really.

Well, with your Modis telling you the IAC is bad, I'm hesitant to tell you other things to look for. But you might be having MAF issues, either poorly grounded, dirty, bad, or it isn't the right one for your swap but I have never dealt with that swap so I don't know anything about it.

I am in no way a professional mechanic, nor do I have any experiance with this swap (as I have a bluebird not an avenir). But from what I have gathered from my own research, that black box (which I believe is the Auxillary Air Control) is supposed to be bolted to your intake manifold. Its open at colder temps to allow more air into the engine during warm-up and closes when the engine gets hot enough.

The Idle Air Control Valve is used to control the amount of air flow into your engine when the throttle plate is closed.

Another possibilty that comes to mind is leaking hoses running to and from these valves or maybe check to see if the AAC is bolted onto the manifold correctly. these are all the little, easy things you should check first. nothing worse than digging into your engine bay for days only to find out the problem was a simple vacuum leak. lol ask me how I know

Whats your coolant temp sensor reading? If the sensor is bad, it may not be closiing it once the car warms up..

Just to clarify, I'm calling the black box under the intake mani the 'air regulator'. All it does is open when the car is cold so the car idles high, and closes when warm to bring idle down. The other thing that bolts to the side of the intake mani I'm calling the 'IAC/AAC'. That's what alldata calls it, anyways. Like you said, it controls air flow when the throttle is closed. I cleaned the crap out of both of these and swapped them for others I had around and it made no change.

Air Regulator in the middle, IAC/AAC in the top right


Using the Modis to check my coolant temp sensor readings, it looks okay. I can let it idle and watch it slowly warm up. Once it hits 211 degrees the fans kick on until it cools to about 205 degrees and repeats. I have about 2 or 3 other coolant temp sensors laying around that I could try out.

And the MAF is reading 1.5v at idle, but when I use the Modis to close the IAC/AAC it reads 1.1v, possibly because its getting less air?

Can a mod move this to the "Turbo" section? I think I might get more help there.

So the car isn't idling with it at 95-100% open, or its idling too high? Is the intake for the IAC before the turbo or after? I've always been told to put mine before the turbo, and it works great for me.