onspeed

Notice this problem lately after adjusting my idle.. with the ISV override, car idles at ~950. If i blip the throttle, the rpm will dip below 950 when returning to idle. The dip is more emphasized when the car is under more load. for example, if i did a third gear pull then disengaged the clutch, the needle will go almost to zero. The red ! light flashes for a brief instant.

Increasing the idle prevents this.. but then the car idles at like 1.1k.

What's going on.

JohnKoaWood

I have seen this, and it can be somewhat eliminated using the TB bypass screw in the top of the throttle body... screw it all the way in, then half a turn out to start.. then from there use it to gain idle stability..

some cars, for whatever reason, seem to bounce a little more than others when returning to idle...

choinga

TPS? I had a similar problem - bought a new TPS and it went away...even though mine was 'clicking', etc...

hot-J

Are you running a bov to atmosphere? That'll do it.

Scott H

If mine is even close to that setting it will not run... would this indicate vacuum leaks somewhere?

choinga

I've seen his car - he's not venting to atmosphere...a vacuum leak is a likely culprit as well...pair that up with a suspect TPS that's not sensing idle properly and that could happen. I don't have any experience running without the ISV but my guess is that might be part of the problem as well. In fact, when I fixed that issue on my car I replaced both the ISV and TPS with new components but I had also replaced all the hard vacuum lines and pulled the CV and all the associated birds nest. But, I had the same issue - and it was more pronounced if you were running at say 40MPH in 2nd gear and then hit the clutch to coast...most times my car would even stall at that point. That combo immediately fixed my problem.

racerxrick

in my very limited experience I've had this happen....it was a vacuum leak.

Tom M'Guinn

Vacuum leaks will do this for sure, especially if the car has a MAF.

onspeed

Vac leak was my first thought too.. although I'm not sure where the leak would be at since all the hoses seem fine. Replaced the smaller ones with the silicon set from LR. Tested the resistance of the TPS with the method on clarks-garage, that seemed fine.

Leaning towards ISV at this point.. seemed to act a little strange when I was adjusting idle.. I'll go ahead and double check vacuum lines I guess.