Drifting STi

Brent951, I unpluged the electrical plug on the ISV and i still have the fluctuating idle.

Hosrom951, how can I test my TPS to see if it's okay?

Drifting STi

bump

Drifting STi

Brent 951, I unpluged the electrical connector on the ISV and it still does it......Should I change it anyway?

TRWright

I've had almost the same problem since I installed my MAF, when you run the car hard, and its warm, and you brake to a stop, the idle will drop to where the car is about to stall, then bounce up and around until it *finds* the idle. It doesn't do it all of the time, but it had been so bad that the car has stalled on two occassions. It's really annoying.

Brent951

Drifting STi,

And you already verified that you don't have any intake leaks? My ISV actually was leaking itself so make sure you try running the car with the ISV hoses disconnected and plugged at the intake manifold side. You should then be able to adjust the idle speed with just the screw on the top of the throttle body.

Brent

Drifting STi

Spoke to George Beuselinck at 944ecology and he said the early 85 does not have a ISV. I saw the samething (ISV) in the pic Brent posted. How can that be? Can George be wrong?

edit: Okay I spoke to Ted, He suggested I disconnect the vacum line that goes to the power brake cylinder since it only happens at idle and when the brake is pressed. So the result.....no boucing idle! but now I don't have power brakes.

Where could the brake system be losing vacum? I hear air loss when I press the brakes sometimes.

Brent951

They have something called an electric air valve 944 606 215 00. I didn't know you had an 944.

Drifting STi

Hey Brent, I spoke to Tedwright, He suggested I disconnect the vacum line that goes to the power brake cylinder since it only happens at idle and when the brake is pressed. So the result.....no boucing idle! but now I don't have power brakes.

Where could the brake system be losing vacum? I hear air loss when I press the brakes sometimes.

TRWright

Glad to see you isolated the problem to the brake booster.

hosrom_951

Sorry, didn't see you're question:

For TPS Click Here


The brake booster takes vacuum from the intake manifold; However, there is a check valve and a rubber seal on the brake booster itself. Check those (the valve should open one way only, under vacuum).

What year is the car? the 86-88(?) have a venturi under the intake, which splits the vaciuum hoses from the brake booster and idle actuator. Later cars don't have that (you can update to the "new" style).

The sound of "air loss" while braking is from the inside of the car? could be just the brake pedal-to-master cylinder/brake booster noise (movement) not neccessarily air loss.

You basically have a vacuum leak, spray some soap + water on the engine (under the intake, hoses as well) and pressurise the system, look for bubbles and listen for leaks.

Hope this helps!!

Drifting STi

Hussam Jamil and Ted, Thank you so much for the help. You guys are amazing.

Hussam Jamil, I have an early 85 944. Do you have a diagram of the venturi system?

Danno

"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."

Classic signs of a vacuum leak after the throttle body... as Hussam says...

[i]"The sound of "air loss" while braking is from the inside of the car? could be just the brake pedal-to-master cylinder/brake booster noise (movement) not neccessarily air loss.

You basically have a vacuum leak, spray some soap + water on the engine (under the intake, hoses as well) and pressurise the system, look for bubbles and listen for leaks."[./i]

On the 951s, the Y-shaped venturi that provides vacuum to the brake-boost is a common source of leaks. Also the large 1/2" hoses tend to leak after rubber shrinks over time (but the hose-clamps can't be tightened). This leak causes variable amount of air to be sucked in and causes a change in your air fuel-ratio. The O2-sensor's readings then causes the DME to try and catch up to the leak by changing fuel, but it's never fast enough and you end up with the rhythmic up and down idle.

Brent had a good method of pressurizing the intake and found that his "new" replacement ISV was bad. Wouldn't have been able to find it without the pressure-test.

Drifting STi

So I'll checkfor leaks. I am going to try with a hose pluged into my ear and the other end poked in places where I think there is a leak. I'll also try the soapy water thing. wish me luck.

BTW I have a early 85 944 NA. Do I have the venturi system?

hosrom_951

Drifting STi: Here is the vacuum system diagram for early cars/cars with the venturi, this is floating around rennlist, who don't really know who to give credits to for this:



You can try spraying carb cleaning around the intake manifold, hoses, connections etc....just be careful, have a fire extinguisher with you, since i HEARD stories of this can cause fires (i do it when the engine is cold )

hosrom_951

*edit*

You're car is an NA, please ignore the vacuum system diagram since it is for the early 944 Turbo models (different).