I was getting off an exit ramp and I was half throttle in 4th gear. The car felt like it made a ton of boost very quickly then just shut off. The motor was still on, but throttle did not work. I pulled over and the car was idling horrible. I had full oil pressure. No new cels. I shut off the car and started it again and idled and drive like normal. I didn't get into boost at all to get it home, but it was still making what it should at part throttle and such. I will do a pressure test tonight, but have any of you experienced this? Car is 100% stock besides a tune and exhaust.

 

went into limp mode/protection..
if a new issue, check your wastegates to make sure they move freely as a starting point and see if the signal/send line has any air leaks to the wastegates (not receiving an open 'signal')

 

First get codes read even if there is no CEL. Then there are a number of possibilities:
1. wastage (as above)
2. Leak somewhere
3. MAF quit
4. Fuel delivery problem
etc.

 

You have a way to log your car? Check MAF readings. My car boosted migh higher then normal when my MAF was going out.

 

You need to log. Number one reason I recommend the Cobb as a tune. Logging capability is worth its weight in gold!

 

Codes..

 

.....

 

P0238
353 Pressure Sensor - Above Limit
Possible fault cause
♦ Short circuit to B+
♦ Open circuit
♦ Pressure sensor faulty

0-18 P0121
117 Throttle valve - signal implausible
Possible fault cause
♦ Open circuit or short circuit in the wiring
♦ Throttle position sensor faulty
♦ DME control module faulty

♦ Fault P0121 only appears in conjunction with fault P1121 or
P1122.
♦ The system operates in pedal sensor standby mode, i.e. the
angle of the accelerator pedal is calculated from the residual
position sensor signal.
♦ The opening angle of the throttle valve is limited to 30 %.
♦ The dynamic of the throttle valve is restricted.

0-110 P1121
430 Throttle position sensor 1 - signal implausible
430 Throttle position sensor 1 - below limit
430 Throttle position sensor 1 - above limit
Possible fault cause
♦ Open circuit in wiring
♦ Short circuit in wiring
♦ Throttle position sensor faulty
♦ DME control module faulty

 

Last TT I worked on with an overboost problem was due to the vacuum line being disconnected between the intake and the N75 valve. Very easy to inspect.....

 

thanks. I did a full leak test. Everything around the n75 was tight. Noticed an upper ic hose has a pin hole in it, but can't find a source that would take in unmetered air.

 

A little suggestion. If you got access to PST2 or Durametric, in the dme section you got possibility of testing two valves which are part of the boost system. The "frequency valve boost control" also called the N75. And the "boost air bypass valve" which is located just under the diverter valve. When selected you can hear a continuous click coming from those valves if they are working properly....

 

Well fixed a few leaks, replaced a hose, did the tb adjustment and the car drove great for 5 hours. Multiple days and pulls. And it happen again. This time part throttle in 6th gear just passing someone. Car rockets off and dies. No throttle. I pull over, restart the car and runs normal again. Since the last time this happen it saw wot probably 100 times. What on earth could it be?

 

Without the current error codes, the behavior suggests an intermittent problem with something related to the E-Gas (a potentiometer) or with the throttle position sensor.

I kind of like a potentiometer, two in fact. In the event one of the two E-Gas potentiometers fails the system should enter limp mode. If both fail then there is no throttle. The DME can't know how far to open the butterfly valve.

 

+1.. me too. overboosting. breakups, idle hunting, all manner of high strangeness when the maf is fried.

vglnte..when was the last time you replaced/cleaned the maf? i am not a believer in cleaning them? but i know once again, that the car exhibits all kinds of disparate symptoms ( that mimic boost leaks/n75 issues/etc, ) when the maf is shot.

 

a long time, but I would imagine a bad maf would act up more than once every 100- 200 times. or so times.