M20 idle problem

[tjohnson97]

Hey everyone, I'm Trevor. I recently purchased a 5 speed manual 1989 325iS. Needs a little bodywork and TLC. My plan is to build it into a street legal drift car. It's going to have full interior, heat, maybe A/C, radio, bucket seats, 5 point harnesses, rollcage, hydro, coilovers, steering angle kit, big brakes, 17 inch wheels, and probably more I'm not thinking of at the moment. I still need to replace all of the preventative maintenance stuff before all this happens though. I'd post pictures, but I'm not sure if I can from my phone, so I'll have to wait until I get on my computer. I apologize if this isn't getting posted in the right spot. I haven't fully figured out how to navigate the entire site.

I've got a bunch of questions I'd like to get answers to, but I'll just post a couple problems for now that I'm having that hopefully you guys will know how I can fix them. So the car runs and drives great (it sat for a year and I drove it 2 hours home without any issues), but it idles at 1000 RPMs, and when at idle if you tap the throttle a tiny bit for a split second the RPMs drop to the point right before it would stall out, but it never gets to the point where it stalls. I'm not sure how to lower my idle to 750 or wherever it's supposed to be. I tried messing with the throttle cables but that didn't do anything. The idle dropping with a quick light tap I'm not sure if that's normal or if there's something I can do to fix that. Hopefully I've described this in enough depth that someone can give me a diagnosis or list of possible diagnoses and what can be done to fix them.

[strad]

Possible vacuum leaks. Intake gaskets, intake air boot, air breather from valve cover to TB. Of course if somebody opened or messed with the air meter it could be part of the problem. Also look at the rubber lines that connect to the idle air stabilizer. Also rubber o-rings seal the fuel injectors into the manifold. Those can fail and cause vacuum leaks.

And yes, I used to own an E30. Currently without one. I bought it in 2005 and somebody wrecked into me earlier this year. Got a nice E38 with the proceeds though.

[superj]

I say vacuum leaks also

[JIM1inWisconsin]

I had two E30's with low idle problems and a turner chip solved problem for both. Something else to consider if all else fails.

[tjohnson97]

I know this thread is kind of old, but I did change all the vacuum hoses and the drop in RPMs after tapping the gas pedal has completely gone away. The throttle response is immediate now. However, the idle is still at 1000 RPMs. I have not really checked anything else that was suggested though. I should add that sometimes it will idle at 750 RPMs after starting it but once the gas is pressed it won't go back below 1000. Seems like it's not something I need to be too worried about, but it'd be nice to use a little less gas at stop lights.

[superj]

the big rubber elbow from the air flow meter to the throttle body usually has cranks in it that can cause this issue. check that out and get a new one. just grab it and look for cracking and splitting between the ribs

[325e '87]

Probably a good idea to take the idle air control off the car and spray a liberal amount of carb cleaner in it to flush it out. You may see some dark fluid pour out, keep doing it and shaking it to move the valve. Both my cars run and drive much better after I did this and replace all the intake side rubber.

One more thing, I had a vacuum leak in the brake booster line. Ended up replacing the grommet on the brake booster and the check valve. I could hear it hiss when I shut the engine off and got my ear close to it.

i don’t know how common a thing this is but I cleaned the throttle body until it looked new and cleaned up/replaced the idle switch (throttle position switch) that sits underneath the throttle body. It has a precise adjustment, make sure it clicks 1-2mm before throttle is at rest and make sure it works using a meter.

[clovett]

I have my 86 running now but I have a question about the idle air control. On the one I have, which is the early fuel injection I believe, the idle air control is on the left side "spark plug side" and attaches to the intake manifold. The later one I think is on the intake rubber boot and I I think a DC motor?

So is the one I have just a valve? I cleaned it and if I shake it I can hear a valve move inside the idle air control. I can also hear a valve when I apply voltage from a 9v battery.

[82eye]

hi clovett.

your iac is number 13 in this pic





internally they are all essentially the same. the difference is mostly just orientation for the vacuum hoses.

you might wanna try a new thread so as not to thread jack in the future

[JamieG296]

Glad to run up on this. I bought an 87 and it has a hard time starting in the morning. It's like 50 degrees here. You have to hold the throttle a little. I'm going to go through it and replace the vacuum lines after I'm done with a full suspension overhaul.
Thanks for posting back with the results though for sure.

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