vetblack

I have done a seach on this but I only found problems of fluctuating idle when cold/start-up.

My car starts fine and when the engine temp hits a certain level (not sure exactly, but around 170-180) the idle starts to fluctuate. It slowly rises to about 1500 rpm then drops back down to a normal idle. Then slowly it rises back up to about 1500 rpm or so then drops back down to a normal idle.

This only happens AFTER the engine warms up.....
Start up and cold idle is fine....

Also, I already checked the TPS sensor, its OK,
I assume the idle stablizer valve is fine since it only happens AFTER the engine is warm.
O2 sensor is fine.

That just leaves the DME temp sensor...


Thanks for the help....

Brent951

Does the same thing happen with the O2 Sensor disconnected? Have you tried changing the idle speed by openning up the idle screw on top of th throttle body to see if that has an effect and keeps it from changing after warming up.? Have you tried blocking off the line from the idle stablizer to the intake to see if the idle is still changing? Those are the things I'd try to at least to find out what effects the idle then you could at least start to figure out what's causing it.

Brent

Luis de Prat

I agree. Did you recently replace the idle screw? It may be on too tight. Does the idle dip to nearly zero rpm when you brake during driving?

Sounds like opening the idle screw just a tad (counter clockwise) would help.

Of course, this is a "quick fix." The correct way to reset the idle is bypassing the ISV with a jumper wire to the ports in the diagnostic socket. Do a search for the exact ports.

Drifting STi

I have the same fluctuating idle on my 1985 944. but my car idles a little above 1000 rpm which I think is a little high. Would opening up the idle screw speed up the idle rpms? I'll try the troubleshooting tips anyway. Thanx and good luck vetblack

Eyal 951

Could be a vacuum leak too, though less likely if its only when warm.
~Eyal

Luis de Prat

In your case, the idle screw may be open a bit too much. I would try closing it slightly (clockwise). It's located on top of the throttle body.

Adjust it in tiny increments until the rpm needle sits right at 900, a notch below the 1 mark.

vetblack

It was a bad ISV !!!!!!! It was stuck open so when I started the car, it fired right up and maintianed a high idle. Once it warmed up, the DME was adjusting A/F misture to compenstate and it kicked in and out of the idle mode. I disconnected the ISV (plugged both ends) and that solved the problem, I had to turn up the idle screw a little (not the air srcrew on top of the throttle body), then readjust the TPS to match the idle adjustment.....

But now it works just like it should......

Drifting STi

Thanx for the info.....I'm gonna try that. I'm also gonna check the ISV vetblack did.

Chas

how exactly does the ISV function? When doing a delete, do you have to make any adjustments to the ecu to fool it into thinking it's still there or anything?

Drifting STi

Can someone post a pic or explain where the idle stablizer valve is? I can't find it.

Brent951

it's below the intake manifold it's T shaped and has a wire and a connector on the top of it. It's diffcult to see and get to without removing the intake manifold. It should be sitting between runners 2 and 3.

Brent

Brent951

Here are a few pics

Brent951

another pic

Drifting STi

Brent951, Thanx so much for the reply. I'll try again now...

hosrom_951

The TPS was faulty when i had a fluncuating idle when warm