Diagnosis needed: Slow returning RPMs

[trry96]

m20b25 manual

Symptoms:
-The RPMs take about 10 seconds to come down from 4k RPMs to idle speed
-Engine Idles at 1k

It doesn't happen all the time. I haven't figured out what triggers it, though it usually happens more frequently when the engine is hot, or after I've flogged it. Half the time my engine runs like a champ...the other half of the time it does this s#*$.

Any ideas?

[asubimmer]

does it do that even if you r3v it from the TB?

[BigD]

Does your pedal actually return to the upright position? Maybe check that the floor mat isn't jamming the pedal (some may laugh but this is a very common problem on E34s, dunno about E30s) and the throttle cable and the butterfly don't stick.

[trry96]

Nah, a little more serious than that. From the TB does it, and I don't have floormats.

Maybe a sensor getting knocked loose or corroded?
Which sensors should I look at?
Could it be clogged injectors/fuel rail?
I switched in platinum plugs (about 5k miles ago) before I read the countless threads saying that platinums are not to be used on m20 engines. Could that be it?

I threw some injector cleaner in the last tank, and it seemed to help marginally. But it seems to me that clogged injectors wouldn't make the idle go up...and they would make the engine run very rough...it isn't running particularly rough, just slow.

I'll tell you though, it's driving me up the damn wall. Every time I have to upshift, I have to wait 4-5 seconds for the RPMs to match.

Thanks guys.

[jlevie]

That sounds like a sticky throttle body or accelerator cable perhaps accompanied by an intake leak.

[trry96]

I don't think it's a sticky throttle body. Intake leak is a definite possibility. I might pull the throttle body this weekend and do some gasket-ing. Thanks.