Cold idle issues and full throttle hesitation

[mszydlo]

I’ve got a 1985 325e and It’s got a couple issues. When the car is cold after about 10 seconds of running the idle will begin to surge and go from 500-1000 rpm. I’ve also find that when I give it full gas ie. Pedal to the floor in neutral it hesitates for a second then does what it’s told. I had a shop do a vaccum test and replace they ended up saying my valve cover was warped and replaced it. I’m not sure what to do now so anything helps. Thanks!

[bmwman91]

Could be a dying O2 sensor. I think that it take smore than 10 seconds after a cold start for the ECU to start reading it, but if it is dying it can cause issues like this.

It might be a sticky cold start or idle control valve. These seem like the most likely culprits.

Other issues might involve a plugged fuel filter, dirty injectors or a dying fuel pressure regulator.

[armadefuego]

One common cause, like bmwman91 says, is a sticky ICV.

It is easy enough to clean up to try cleaning first.

I believe there are _distructions_ on this site, somewhere.

The other possibilities require a little, but not much, more work.

[tomstin]

I would be curious to know what "vacuum test" they did. Smoke test? These engines are very sensitive to vacuum leaks. Intake boot is a common failure point. Throttle position switch is worth checking. Idle control valve would be next. Then you may want to check the temperature sensors.

The best, all in one place on idle issues is here: http://www.verrill.com/car/e30_idlefaq.shtml

[Gregs///M]

Definitely sounds like a vacuum leak but also consider a failing AFM as it has a temp sensor in it and will cause hesitation as a failure.