I have been going through all of the various issues that this new (to me) car had since I bought it last year, and I have almost everything sorted out except for two things. The previous owner had just replaced the timing belt, water pump, EGR system, cam, lifters, flywheel, clutch, transmission fluid & filter, fuel filter and a number of other small things before I bought it. So the car has ~209K miles on it, with all of that service being done at around 200K. That's the background, and here are the 2 issues I can't figure out.
1) Grumbling noise from front end / engine in 5th and 6th gear at highway speed.
It sounds sort of like a dying wheel bearing, but the noise is really only present above 60MPH and does NOT vary when I am turning.
It seems to be totally dependent on output torque / throttle position. Applying more throttle makes the grumbling louder, or if the car is on a road that undulates up and down, the noise gets louder as the car hits bottom and starts the uphill part of the bump. I can hear it a little in 5th gear on smoother roads, but it is most apparent in 6th gear. I really can't tell if it is the engine, transmission or drivetrain. Wheel bearings, axles, or a bearing in the transmission all seem like likely culprits, but I am not familiar enough with these cars to know what the common issues are.
2) Engine surge in 2nd gear.
About 90% of the time, if I get going from a stop with the throttle held steady at a "normal" / not aggressive position, the car will behave consistently through first gear, hit ~2500RPM and shift to 2nd gear, rev normally up to about 2500RPM and then give me a burst of power up to 3000-3500RPM before shifting to 3rd and resuming normal behavior. Again, my foot has not changed position on the throttle when this happens, and the only way to stop it is to lift off of the throttle a bit as 2nd gear approaches 2500RPM.
The car did have a BIG boost leak which I fixed shortly after buying it, and I have taken readings with VCDS to see if the air flow values are close the expected ones. Here is a log I took over a couple of minutes of mixed driving (idle, normal accel, 100% throttle accel, cruising). Actual boost tracks well with expected boost, except at very low throttle and coasting, where it seems to read a little high. The expected EGR/air flow and actual/MAF flow also track well, except under low throttle and coasting where they read fairly high. Is this an indication that the VNT actuator is either sticking at the low end, or the lower stop is set improperly? The previous owner did say that he had not replaced the turbo.
As far as looking at DTC's in VCDS, there are none for the engine and one for the DSG:
P1793 - Transmission Speed Output Sensor (G196) No signal - Intermittent
Based on the tech ref document for the DSG, I don't think that this is related.
1) Grumbling noise from front end / engine in 5th and 6th gear at highway speed.
It sounds sort of like a dying wheel bearing, but the noise is really only present above 60MPH and does NOT vary when I am turning.
It seems to be totally dependent on output torque / throttle position. Applying more throttle makes the grumbling louder, or if the car is on a road that undulates up and down, the noise gets louder as the car hits bottom and starts the uphill part of the bump. I can hear it a little in 5th gear on smoother roads, but it is most apparent in 6th gear. I really can't tell if it is the engine, transmission or drivetrain. Wheel bearings, axles, or a bearing in the transmission all seem like likely culprits, but I am not familiar enough with these cars to know what the common issues are.
2) Engine surge in 2nd gear.
About 90% of the time, if I get going from a stop with the throttle held steady at a "normal" / not aggressive position, the car will behave consistently through first gear, hit ~2500RPM and shift to 2nd gear, rev normally up to about 2500RPM and then give me a burst of power up to 3000-3500RPM before shifting to 3rd and resuming normal behavior. Again, my foot has not changed position on the throttle when this happens, and the only way to stop it is to lift off of the throttle a bit as 2nd gear approaches 2500RPM.
The car did have a BIG boost leak which I fixed shortly after buying it, and I have taken readings with VCDS to see if the air flow values are close the expected ones. Here is a log I took over a couple of minutes of mixed driving (idle, normal accel, 100% throttle accel, cruising). Actual boost tracks well with expected boost, except at very low throttle and coasting, where it seems to read a little high. The expected EGR/air flow and actual/MAF flow also track well, except under low throttle and coasting where they read fairly high. Is this an indication that the VNT actuator is either sticking at the low end, or the lower stop is set improperly? The previous owner did say that he had not replaced the turbo.
As far as looking at DTC's in VCDS, there are none for the engine and one for the DSG:
P1793 - Transmission Speed Output Sensor (G196) No signal - Intermittent
Based on the tech ref document for the DSG, I don't think that this is related.
