EPC light and RPM fluctuation

[eldiablo1]

A few weeks ago while driving on the highway, the car sputtered / died and EPC light came on as well as "!" cruise control fault.

Started the car back up and it drove okay for a few miles, then it started to sputter and got CEL (code P0121 - Throttle Position Sensor). Idle would oscillate wildy (when stopped or moving) from 800 rpm to 2000 rpm with no gas applied.

Was near VW dealer so I drove it there. Dealer replaced throttle body and re-pinned the wires to the throttle body ($1200). Symptoms came back so I returned to VW. They once again re-pinned the wires and said that if it happens again, it's probably due to the fact that I am tuned (APR stage 1). Service manager took the time to tell me he flagged the vehicle as TD1 (like it matters at this point with 82k miles) and said that if it happens again they will need to replace the ECU and wiring harness.

Issue came back very next day.

I replaced coilpacks, cleaned MAP, MAF, and AIT sensors. No difference.

Others have noted similar experience on this site but no definitive root cause or solutions have been communicated. Issue is also documented on other sites as well with no clear answer.

I'm at a loss. If my wife hadn't lost her job recently, I would just trade her in. On a bright note, the weather will be cold for the next few days.

Thoughts?

Conclusion: After several weeks and unfortunate mis-diagnosis from VW, this issue was finally resolved by replacing the engine wiring harness.

 

[TheGolfGTI]

Have you check the pedal voltage? VCDS you can log the Throttle pedal vs the TB. Might tell you if it is a throttle pedal sensor, or might be a way to shot the wires and check for a voltage drop.

 

[eldiablo1]

Thanks man. Car is back at the dealership. Hoping they can effectively diagnose the problem. I have a hunch it is something in the wiring harness.

 

[herrerafavian2]

Idk man I would honestly suggest taking elsewhere if possible and having it re-diagnosed. Almost sounds identical to the symptoms mine had when they replaced the intake manifold. Keep us updated though! Best of luck.

Sent from my SM-G960U using Tapatalk

 

[eldiablo1]

Update from dealer...

After conducting their diagnosis, according to the service manager, in addition to the original P0121 code, they pulled multiple other codes ranging from MAF faults to ECM faults to cylinder misfires to RPM unexpectedly high / low, etc etc codes of all sorts…. He read them to me over the phone but I do not have the actual codes.

He is indicating that the APR “chip” is causing these problems because in his words, “the chip allows the car to exceed the rev limiter so it is throwing codes”.

Anyway, it’s pretty clear this dealership may not have the talent to diagnose any issues beyond simply scanning via OBD II. He seemed unwilling to conduct any additional trouble shooting and suggested I just pick up the car in its current state.

I told him since I’ve already spent $1200 on a misdiagnosis, I would rather his lead tech took the time to actual identify the issue and work to resolve it. Further, I think I deserve a credit for the misdiagnosed work on any future repairs.

They are now indicating that it is a ECU issue but they can not find an ECU anywhere in the US. They are working to locate one. Hard to believe. I'm going to call around tomorrow to see if I can find one... assuming that the ECU is the actual issue.

 

[dead_catz]

Update from dealer...

After conducting their diagnosis, according to the service manager, in addition to the original P0121 code, they pulled 50+ other codes ranging from MAF faults to ECM faults to cylinder misfires to RPM unexpectedly high / low, etc etc codes of all sorts…. He read them to me over the phone but I do not have the actual codes.

He is indicating that the APR “chip” is causing these problems because in his words, “the chip allows the car to exceed the rev limiter so it is throwing codes”.

Anyway, it’s pretty clear this dealership may not have the talent to diagnose any issues beyond simply scanning via OBD II. He seemed unwilling to conduct any additional trouble shooting and suggested I just pick up the car in its current state.

I told him since I’ve already spent $1200 on a misdiagnosis, I would rather his lead tech took the time to actual identify the issue and work to resolve it. Further, I think I deserve a credit for the misdiagnosed work on any future repairs.

They are now indicating that it is a ECU issue but they can not find an ECU anywhere in the US. They are working to locate one. Hard to believe. I'm going to call around tomorrow to see if I can find one... assuming that the ECU is the actual issue.

Damn i hope it gets resolved. I have one hard fast rule and that is to never let my car touch the dealership once I drive it off the lot. They will fuck you over while being incompetent and performing repairs incorrectly

 

[eldiablo1]

Taking the car today to a different VW dealer that is also an APR dealer. They will pull the APR tune off the ECU and load the stock tune to conduct proper diagnosis. Hope this results in something productive.

 

[eldiablo1]

Dealer called and indicated that they removed the APR tune and restored ECU to stock tune. Issue can no longer be replicated and no codes at this point.

They are going to put some more miles on it to see if issue returns.

Odd to think that the tune itself could have been causing the issues. We shall see...

 

[eldiablo1]

Dealer confirmed that they put 65 miles on the car today and could not replicate the issues. Root cause of the problem is pointing to the APR tune itself. I will email APR in the morning once I have the car back.

Has anyone ever experienced this? I am picking the car up tomorrow, but with the stock tune. Not sure if I should risk getting the car re-tuned again. Bummer.

 

[zrickety]

It could have been a corrupted flash. I wouldn't hesitate trying again. Assuming the ECU is still good. Do you know if it was taken apart before (the old way) or just flashed through the port?

 

[eldiablo1]

It could have been a corrupted flash. I wouldn't hesitate trying again. Assuming the ECU is still good. Do you know if it was taken apart before (the old way) or just flashed through the port?

ECU had to be opened by APR for the initial flash 4.5 years ago (ECU had bricked during the initial port flash process). Updates were made this time around through the port without any problems.

I drove the car about 30 miles today and it felt great on the stock tune. No issues whatsoever.

Hard to imagine that a tune would become corrupt after all this time with no issues. :iono:

Emailed APR for their perspective.

 

[PunchBuggy]

I'm having the same symptoms as you but do not have a tune on it. Just bone stock. Mine seems to run fine for weeks and then it will show those same symptoms multiple times in days then back to normal. Searching the net it's pointing toward throttle position sensor but I haven't tried doing that yet. I'll keep and eye on this thread good luck with yours and if I do change the sensor will post results.

 

[eldiablo1]

Issues came back again last night after putting about 100 miles on the car since the ECU was returned to stock. So at least I know it's not the tune.

Will return to VW dealer ASAP to hopefully diagnose this issue once and for all.

 

[eldiablo1]

I'm having the same symptoms as you but do not have a tune on it. Just bone stock. Mine seems to run fine for weeks and then it will show those same symptoms multiple times in days then back to normal. Searching the net it's pointing toward throttle position sensor but I haven't tried doing that yet. I'll keep and eye on this thread good luck with yours and if I do change the sensor will post results.

good luck! Please post your progress.

 

[eldiablo1]

Update - Issue diagnosed as faulty wiring harness. Getting replaced next week ($1700 + tax). Merry Xmas to me...