Ky944TurboNewbie

This is my second go around on this problem. At first I thought it was the TPS, but when I re-read the Clarks Garage diagnostic for the TPS, I think the readings show that it is working good.

My problem started with a very rough idle when I let off the gas and I barely limped the last mile home. Once home, it sat for a couple of weeks before I found time to work on it.

I was able to hear and fix a huge vacuum leak. However, now it is running very rough at idle.

I tested the MAF and TPS and have confirmed both of those are good. I just used some carb cleaner looking for any additional vacuum leaks and wasn't able to find any. I have disconnected the O2 sensor and didn't notice any change in the way it idles.

The engine idles at about 900 rpms, and when I give it a little gas and let off, the rpm's will dip to about 5-600 and the engine may stall at that point, or return to 900 rpm's and keep running. I hear what appears to be a slight popping noise like a small backfire after I let off the gas.

What should I look at next? Do I need to retest anything or should i be looking at something else? Do i need to pull the plugs to see if it they look fouled?

Thanks,

Michael

Bri Bro

First, set your idle using the procedure at Clarks.
http://www.clarks-garage.com/shop-manual/fuel-08.htm

Ky944TurboNewbie

I currently don't have the round connectors needed to do jump the diagnostic plug. I will have to run to the auto store to get them. Anything else I can check so I don't have to make a bunch of trips?

Ky944TurboNewbie

I just let the car warm up and it is still having a hard time returning to idle when warm also. It has been awhile since the car has been out for a run, so maybe it is just some carbon burning off, but there was more white smoke coming out of the tailpipe that I would have expected.

Black51

It sounds like your ISV may be bad.

Does the car run well when off idle? If it does run well off idle,then this would be the next thing I would check after resetting the idle.

Do this only after knowing you don't have any vacuum leaks. You'd know you don't have any if the car hits full boost like normal.

Bri Bro

You don't need a connector, just use a piece of wire to make the jumper and push the ends into the sockets. I have a feeling your idle is set too low and the engine is dropping to low in RPM before the ISV kicks in and brings the idle back up. The reason it is too low may be related to the car not running for a while, SO, after you run it for a bit and get new gas in it and some miles on the engine, you might want to set it again.

Ky944TurboNewbie

I cannot hit full boost like normal. If I open the throttle, it gets to about 1 and 1/4 to 1 and 1/2 bar before it starts to cut out. As long as it is below 1.25 it runs great. Does this point to a vacuum issue?

Black51

It could be a vacuum issue. Could also be other things. Check your vacuum lines by pressurizing the system.

Go on Youtube and copy and paste "DIY - how to pressurize your 944 turbo intake system". It's a great video on testing the vacuum system. It may be that your vacuum problem doesn't appear until the car is under boost.

But with the rough idle also happening, something else seems to be causing trouble. That, or the car might have multiple issues.

Start with checking your spark plugs and ignition system. When were the plugs, wires, rotor, and coil changed last?