I have something wrong in my 996TT. The idle is unstable....

Sometimes while shifting, the rpm's spike without pressing the gas pedal
Sometimes after putting the car in neutral, it idles at 1500rpm and then starts to slowly go into the 900rpm range (Tune file by Markski normal idle is 900rpm). Sometimes it idles at the 1100rpm range for some minutes and went to normal when I press the gas pedal.
I did a leak test and did not find any leak at vacuum line. I did a reset TB too.

What I should check or replace?

Thanks,

 

Sounds like a vacuum leak somewhere. How positive are you everything tested for the boost test very well with no leaks?

When you did the TB alignment, I presume everything went fine with no errors? Any codes stored on the car?

 

The mechanic did the leak boost test with the correct tools from the turbos. Close one turbo and put air from another one. The line did not lose pressure.

But if it is a leak vacuum, it is normal that the idle issue happens only sometimes?

The DME has not error codes in memory.

Thanks,

 

Ah, mechanic done boost leak. . . Was it a smoke test or boost leak? Two kind of different things both trying to accomplish the same goal.

Markski will tell you his opinion of "professional mechanic" performed boost leak tests. Most on this board feel you really need to test the system under pressure to at least 15psi and for it to hold there continuously for a good period. It shouldn't be a 5psi test that is "good enough". And if tested to 15 or 20psi, it needs to hold for a good period of time, not immediately start trailing off.


Does the idle issue occur with cold starts / hot starts / whenever? With a small vacuum leak, it can seem to be intermittent and can be dependent on cold stat/warm start sometimes.

 

I spoke with Markski about this problem.

The idle issue occur sometimes with cold starts, hot starts and while driving!!!!

Thanks,

 

Sounds like a MAF going.

 

No isnīt the MAF. No error codes and I tested with another two MAFs.
The car is running very well and strong (1.4Bar).

Thanks,

 

check the TB for carbon/sludge build-up around the flap area

 

What did Markski say. To my knowledge, that usually sounds like a vacuum leak/check valve, etc.

 

How long has it done it for? ... Over night or gradually worse?... It definitely is searching/hunting for idle...How does it respond with the A/C on ?
By any chance did you check the rubber TB coupler from Y-pipe?
Good Luck..

 

Markski told me that probably it is a leak.

After I spoke with Markski my mechanic did the leak test with lot of PSI. No leak detected!

 

Mine was an O2 sensor.

 

This idle issue started a few months ago after installing the GT3 pulley.

I didnīt check with the A/C on but I will do it.

Not only over night, at day too and is is always the same instability.

When the mechanic did the leak test he checked all the hoses and connections too.

 

Your car had the same idle instability?

Any error codes stored on the car?

Thanks,

 

your car run strong under boost, but if you are at idle your car have a issue.

For my understanding its not a boost leak at pressure side, may be it is a vacuum leak before the turbo / but at this point you check it with break cleaner and (not to hot engine...be carefull)check if your idle changes when you spray at the intake lines