stomachbuzz
Well-known member
So I got a car, with some problems. Let's call it a problem car.
Recently bought it with many issues layered over each other. Car was in trans limp mode, no power, etc.
Replaced trans sensors, trans good as new.
Still no power.
Replace all vacuum lines. Tested check valve. All looks good. I tested turbo actuator with MityVac. Did not measure travel, only confirmed correct movement.
Has power sometimes under certain conditions, but 90% no power.
MAF 101 threads combined with VCDS show tell tale signs of a bad MAF.
low power, actual MAF reading is accurate to requested reading up to ~400 then falls off, and car runs better with MAF unplugged
check, check, and check.
I replace MAF ---> ZERO change.
I look more carefully at VCDS, the MAF is fully capable of reporting 700+ (actual MAF readings occasionally spike to 700+), but the harder I press the throttle, the worse the MAF single gets.
When pedal stays at 100%, you can see the MAF signal oscillate in a damped fashion, almost like someone is jiggling the signal wire.
Very evident here:
If the pedal is suddenly floored, then the requested MAF signal (green) stays where it supposed to be, but the actual MAF signal (yellow) half-way spikes once, then it oscillates and declines. The car surges identically to the yellow line.
Very weird.
Sometimes the MAF will work properly, as seen here
Strong boost was present in both of these spikes, and the car pulled well.
The bad MAF signal is infinitely repeatable, and is 90% the norm, as demonstrated here:
and here:
While driving it this ^ time, it was literally ON/OFF with the throttle pedal. 0 or 100.
In VCDS, I also checked the boost data (data block 011). The actual vs requested boost graphs look identical to the MAF graphs.
At this point, with my limited knowledge, I'm confident that the turbo system is working correctly. I believe it is properly following orders based on a bad MAF signal.
The issue is, what would cause the MAF signal to fluctuate so much during constant inputs?
At this point, it almost seems electrical - reminds me of an RC circuit...
Any ideas?
EDIT: I have figured out somewhat of a pattern of when the cars makes power. At low RPM, and low throttle, it seems "okay". If I floor it, power gone as shown in graphs above. But if I gently increase the throttle, the MAF reading will sometimes "catch" and act properly for a while. Also, starting from a stop and flooring it in 1st gear seems to be immune from this issue. As soon as it shifts into 2nd gear, all power lost again.
Recently bought it with many issues layered over each other. Car was in trans limp mode, no power, etc.
Replaced trans sensors, trans good as new.
Still no power.
Replace all vacuum lines. Tested check valve. All looks good. I tested turbo actuator with MityVac. Did not measure travel, only confirmed correct movement.
Has power sometimes under certain conditions, but 90% no power.
MAF 101 threads combined with VCDS show tell tale signs of a bad MAF.
low power, actual MAF reading is accurate to requested reading up to ~400 then falls off, and car runs better with MAF unplugged
check, check, and check.
I replace MAF ---> ZERO change.
I look more carefully at VCDS, the MAF is fully capable of reporting 700+ (actual MAF readings occasionally spike to 700+), but the harder I press the throttle, the worse the MAF single gets.
When pedal stays at 100%, you can see the MAF signal oscillate in a damped fashion, almost like someone is jiggling the signal wire.
Very evident here:
If the pedal is suddenly floored, then the requested MAF signal (green) stays where it supposed to be, but the actual MAF signal (yellow) half-way spikes once, then it oscillates and declines. The car surges identically to the yellow line.
Very weird.
Sometimes the MAF will work properly, as seen here
Strong boost was present in both of these spikes, and the car pulled well.
The bad MAF signal is infinitely repeatable, and is 90% the norm, as demonstrated here:
and here:
While driving it this ^ time, it was literally ON/OFF with the throttle pedal. 0 or 100.
In VCDS, I also checked the boost data (data block 011). The actual vs requested boost graphs look identical to the MAF graphs.
At this point, with my limited knowledge, I'm confident that the turbo system is working correctly. I believe it is properly following orders based on a bad MAF signal.
The issue is, what would cause the MAF signal to fluctuate so much during constant inputs?
At this point, it almost seems electrical - reminds me of an RC circuit...
Any ideas?
EDIT: I have figured out somewhat of a pattern of when the cars makes power. At low RPM, and low throttle, it seems "okay". If I floor it, power gone as shown in graphs above. But if I gently increase the throttle, the MAF reading will sometimes "catch" and act properly for a while. Also, starting from a stop and flooring it in 1st gear seems to be immune from this issue. As soon as it shifts into 2nd gear, all power lost again.
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