|
Just had the EXACT same problem. The vacuum line to the butterfly valve in the muffler was leaking. So my symptoms were as follows.
No power off idle. A Drivetrain Malfunction after driving about 30 minutes. It seemed to reset after sitting all night.
It took my shop two days to diagnose the issue. The faults indicated were:
Boost Pipe pressure Implausable (low)
MAF too high.
These two faults contridict each other.
The only way to diagnose was to drive the car for AN HOUR hooked up to telemetry and capture the failure. And they did just that.
The printouts showed a sporadic fail where the commanded boost did not match actual boost.
The vacuum system has a reservoir and under high RPM, can recharge a little even with a leak. But at idle or cruise speed in 8th grear, there is not enough engine RPM to keep the system charged sufficiently. Sooo... I had no power down low. as there wasn't enough vacuum to operate the wastegate and hence, no turbo. The power would build as engine RPM increased and enough vacuum was there to open the wastegate. But then you'd slow for a stoplight and all the vacuum would go away.
Once we knew there was a vacuum issue, it didn't take long to isolate it to the vacuum line that feeds the exhaust valve. They plugged the valve. It now remains open all the time. Everything is back to normal. I was able to participate in the trouble shooting and was fascinating to watch them zero in on the problem!
|