Audi a3 1.8 turbo overboosting

[manisong]

Hi i have a n audi a3 1.8 turbo 1998 model, when throttle is fully open the car chokes and wont excelerate this only happens when the gas is fully applied, if i steadily increase speed with half throttle i have no problems, no warning lights on the dash. have put it on a computor and it says turbo overboosting any ideas of how to fix this issue

[Mastodon2]

It would be worth posting this in the VAG subforum too, you will probably get some more in depth answers. If it's the 1.8L 20VT engine, I had the same in my Cupra R so I know it a bit. Off the top of my head, a few things that can cause overboosting:

• A bad remap overstretching the boost ability of the car
• A faulty wastegate actuator on the turbo causing it to stick shut and not vent boost pressure as the throttle closes
• Aftermarket dump valves that have too strong a resistance spring for the boost pressure of the engine, the pressure is insufficient to force them open, so boost pressure does not fall quickly enough on a closing throttle and the ECU registers and overboost. Poorly maintained dump valves can stick shut too, they need to be serviced rountinely with cleaning and lubricant
• Turbo intake pipe collapsing under boost, this causes an intake pressure spike which can be registered as an overboost. The TIP degrades and gets softer over time and becomes more prone to collapse under high pressure. Most Cupra R owners fitted the aftermarket Forge or Badger5 TIPs, which were much stiffer and more robust.

While you are at it, look at all the pipework and tubes from the turbo system (there are loads on the 20VT engine) and check for holes, splits, blown-off hoses etc.

[mattmoxon]

sounds like a faulty waste gate, as posted above sticking shut, my focus st had a similar fault.

[aka_kerrly]

Also worth considering cleaning the maf sensor. If you unplug it and go for a drive you can see if the problem is better or worse.

If you have access to it VAG COM ought to give you an idea of what is going on.