hunting idle after hot start?

[Vincent Brick]

Occasionally when restarting my car after being driven and already at temp, the idle will hunt REALLY bad 0-3000 rpm for a few seconds if I don't give it gas, to the point where if it doesn't stall it will come so close the oil light will flicker on. Usually within a few seconds and/or giving it some gas and it clears up. Engine has 200k miles but was just resealed and has good compression, the car runs fantastic otherwise. There's the slightest of RPM variation at idle sitting at lights, but nothing I would really consider abnormal.

I'm guessing ICV? Its only happened a few times, I'm not horribly concerned, but would prefer to correct it if possible.

Thanks for any insight.


EDIT: It seems to only happen immediately after I fill up with gas. Does that indicate anything?

[dnguyen1963]

Check the elbows going into the throttle body. Hunting idle when warm is often the result of loose elbows.

[BMWManiac]

Never a bad idea to have the motor smoke tested for vacuum leaks to eliminate this issue first....this is the hardest to troubleshoot and the easiest to first dismiss.

I would check the ICV, and the intake boot as mentioned. Original AFM?

[dnguyen1963]

Smoke test is a great idea, but it often misses this leak because these elbows will be sucked in tight under vacuum when the engine is running and will not always come loose. The best way to find this leak is to get the engine hot, stop the engine, then wiggle the elbows. If you can move them then they are loose. JB weld the suckers and call it done.

[Vincent Brick]

Literally nothing on the car is original. It has only been about 6 weeks since the new (used) long block was resealed and installed by my roommate and myself at the independent BMW shop he is a mechanic at. AFM was replaced with a seemingly good used unit four months ago.

I'll double check the clamps on the elbows and see if I can get it on a smoker. I think this will literally be its 6th smoke test in 8 months, I'm starting to wonder if E30 owners should purchase such devices of their own lol.

[dnguyen1963]

There are no clamps on these elbows.

[crappycoco]

Should be sealed with rtv.
He's not talking about the coolant "elbows" on the TB. Those have clamps.

[Vincent Brick]

Funny, all of those have clamps on mine. The proper BMW ones too, like they should be there. We're talking ICV and breather hose connections, right?

[dnguyen1963]

Nope, aluminum elbow going into the throttle body. At the very top of the picture.

[Vincent Brick]

I think I've noticed a pattern..... I think it only does it immediately after filling the gas tank. I don't think its ever really done it otherwise, though there is a very slight idle fluctuation pretty much all the time when the car is good and hot, I believe it has only done it to the point of stalling, or would stall if I didn't give it gas, after fueling up. I pretty much only go to the same name brand gas station, and I never let the tank get below 1/4 tank. Does that mean anything to you guys?

I'll look into the clamp thing, at worse I have clamps on stuff that doesn't need it.