I am hoping to get some advice from you guys about issues on a MK4 GTI that a friend of mine just bought. We have spent a few days already troubleshooting but still not found a solution.
So at the start when driving the car we discovered it was going into limp mode sometimes and only boosting 5 PSI until the car was switched off and on. There is no EML or any fault light. The car is tuned but everything else stock except a catback exhaust, boost gauge & BOV.
The first thing we did was pull off the aftermarket BOV that was installed and connect the stock DV. This did not solve the issue.
Next we did a scan with VCDS. We discovered it had code
"17963 - Charge Pressure P1555 - 35-10 - Maximum Limit Exceeded - Intermittent" and
"17705 - Pressure Drop between Turbo and Throttle Valve (check D.V.!) P1297"
When we cleared these codes the RPM started fluctuating. It would drop a few hundred rpm at idle every few seconds and almost stall the car. Eventually after a minute or 2 idling it would log the P1297 code and then it would idle fine again until it was cleared.
Next we tried to test for leaks. We pressurised the system with about 6 PSI from a compressor starting at the pipe that connects to the air box. There was a small leak from a boost pipe underneath that was fixed by just tightening a clip but then there was a lot of air escaping around the pipes in the front of the engine around the dipstick area. After some time checking all the pipes here we discovered there was a crack on the dipstick holder and the air was escaping there. So we removed the holder and plugged it up as best we could with a rubber pipe until we can get a replacement (Still a small amount of air leaking here). This still did not fix the idle issue once the P1297 was cleared.
We discovered that when unplugging the MAF sensor and clearing the P1297 code the car would idle fine and no faults would show up. As soon as the MAF was plugged back in it would almost stall again until the P1297 fault was logged. The MAF sensor was also not genuine so we thought it must be the problem and got a new genuine replacement. This did fix the idle issue when the P1297 is cleared. The code does not come back while the car is idling. However the car is still going into limp mode when it is driven hard and when this happens it still logs the same 2 codes P1297 Pressure drop code and P1555 Charge Pressure Max Limit Exceeded.
So we still have both error codes but P1297 is not showing up at idle anymore.
Next we logged boost pressure, actual & specified in 3rd gear and the car is over boosting until it goes into limp mode. See graph below.
At this point we are not quite sure what to try next. :banghead::banghead::banghead:
We have 2 codes. Pressure loss due to vac leak and over boost. We might try the leak test again when we replace the dipstick holder as a small amount of air was leaking from here even after we put the temporary pipe on. Perhaps once that is sealed correctly we will find another leak. This leak didn't effect the car at idle. Even removing the oil cap at idle has no effect at all. Is that normal because I know on the MK5 GTI it would almost stall if you removed the oil cap or dipstick due to the pressure change?
Also can a VAC leak cause over boost anyway. Perhaps we are looking at 2 problems here. Could it be a bad tune/remap?
Any help would be greatly appropriated.
