Nagging idle problem M20

[dovstar]

I have a problem with my car that my mechanic has been trying to solve but it still persists in a minor way.

When I am in idling in Drive (at a light for example) the idle seems slightly lower than spec which is causing a lot of vibration. The car is fine accelarating and seems to be fine when I'm idling in Park. There is a bit of lag when I depress the accelerator. The way it is running right now a big improvement over how it was before the mechanic got to it. Before, it would start then immediately die or it would start but the idle would hunt around. Also the the idle was around 500 or 1000.

I had the idle air control valve replaced as well the throttle sensor was adjusted and set to factory spec.

What else could it be?

[tfritz]

sounds like it could be either a fuel filter or fuel pump

[dovstar]

I forgot to mention that he pulled the fuel pump and it was okay and he did replace the fuel level sender.

[Goat128]

try a fuel system cleaner like techron. also do a google search for a web site called unix nerd, he has lots of good info on older bmw engines.

[zfender14]

I had the same problem, replaced idle control valve and fuel pump and the problem persisted. It turned out to be the intake hose because it hade cracks and slivers and wasnt sealing properly. Watch out with mechanics, they tried to talk me into buying a new AFM and after the new boot the car runs great and does not have that horrible vibration in Drive idle.

[sp33dbump]

When replacing my belts last weekend I noticed a crack in my intake hose. I didn't feel like running to the parts store again so I used some electrical tape to cover the whole thing. A little ghetto but it worked.

I noticed mine would start to idle erratically after it was warm and I was at a stop. My guess is that the hose would warm up and the crack would spread open more. Now everything runs great.

[dovstar]

Thanks, guys. I'll definitely check this out.

[dovstar]

I just want to double check. When you say air intake hose you mean the straight one and not the one that goes to the throttle body?

[LJSE34]

Probably the one the right. Back when I had my M20 E34, considering maintenance is up to date, cleaning out the idle control vale, throttle body and (especially) re-adjusting the throttle cable gave me some really nice idle and acceleration results. Adjusting the throttle cable is something you'll have to tinker with. These engines will develop some slack with it.

[zfender14]

Yes, check the curved one on the right, if that doesnt work try ebay for a new AFM but be careful, just because the seller says it works doesnt always mean it will. I have bought several for little projects and I would say at least two of the ones I purchased did not work properly.

[EngPhys09]

My M20 just had that problem too it was a manual though but all i did was replace the O2 sensor, it help lean out the car now, no more 15 mpg

[hoboclown918]

I had the same problem, I swaped the ECU, it didnt help. Finally I just adjusted the idle stop screw and that seemed to fix everything.