High Idle After Warming Up

[playdoh850]

Hello everyone!

I am looking for some suggestions on where to start looking to fix my current idle issue on my 1991 318is. When I start my car up it idles a little rough around 900 RPM and then after 10-15 seconds and a rev or two it is smooth. As the car warms up the RPM creep up too. When the car gets up to full operating temp the car idles at around 1400 - 1500 RPM.

I just replaced every hose under the intake manifold hoping that this would resolve the issue since the old ones were cracked and dry rotted. When I did all of the vacuum and coolant lines under there I also replaced both coolant sensors, injector o rings, throttle body gaskets, and the intake manifold gaskets. I sprayed a bunch of carb cleaner through the ICV too. Once warm I am still idling around 1500 RPM after replacing all of that.

Any suggestions on where to look next or what to test?

Thanks!

[bmwman91]

Sounds like a vacuum leak, although it sounds like you replaced vacuum items and checked for leaks. It could be the ICV getting stuck. All the oil vapor in the PCV system gums it up, and just spraying carb cleaner though might have dissolved it and allowed it to drip/settle elsewhere. I recommend taking the ICV out and bathing it in a cup of 99% isopropyl alcohol (ONLY >99%, not 70%). Shake it around, move the little door with the end of a Q-tip to get the alcohol through the moving bits, do this a few times, shake it out well and then let it dry overnight.

[MrBurgundy]

Check the TPS

if there's no signal from the TPS at closed throttle, the ICV will stay wide open IIRC

[playdoh850]

I checked the TPS today. Everything tested within spec. I am going to try a different ICV tomorrow.

Check the TPS

if there's no signal from the TPS at closed throttle, the ICV will stay wide open IIRC

[playdoh850]

No improvement using a different ICV. I am thinking maybe it it the AFM? It only happens once the car is warm which makes me think some sort of sensor and not a vacuum leak?

[jaredmac11]

High idles, inconsisten idles... my thoughts are if ICV and vacuum leaks are verified resolved and worked out, it would be AFM. perhaps confirmation bias since I just went through this.