Intermittent boost...what to check

[willg54]

Got the blink codes out and got 2121 throttle sensor problems by the looks of it! Could this be causing this problem?

It didn't do it today but it went through a time of dropping boost at 3200 to 3500rpm then coming back on full boost but only at full throttle.

Sent from my GT-I9300 using Tapatalk 2

[newsh]

2121 is the closed throttle switch, if there's a short this would be telling the ecu to control idle.

[willg54]

2121 is the closed throttle switch, if there's a short this would be telling the ecu to control idle.

So im guessing that wouldn't be giving me the problems i'm getting?!

maybe it's just a dodgy map...

[newsh]

The ECU uses only 2 signals from the TPS
1/ closed throttle which is the microswitch closed. Instructs ECU to control idle.
2/ WOT (which is actually about 70% and above IIRC) instructs ECU to control boost with WGFV.
I've had a couple of TPS related boost problems,
Throttle cable slack meaning WOT not achieved so WGFV not working.
Dodgy map, data blocks missing from map meaning the very last bit of the throttle the boost dropped out (temp fixed by slackening throttle cable, final fix by getting Mihnea to write the rest of the map!)
I'm not sure what happens if the idle switch is closed but the throttle is open, maybe the boost will be reduced.

[willg54]

The ECU uses only 2 signals from the TPS
1/ closed throttle which is the microswitch closed. Instructs ECU to control idle.
2/ WOT (which is actually about 70% and above IIRC) instructs ECU to control boost with WGFV.
I've had a couple of TPS related boost problems,
Throttle cable slack meaning WOT not achieved so WGFV not working.
Dodgy map, data blocks missing from map meaning the very last bit of the throttle the boost dropped out (temp fixed by slackening throttle cable, final fix by getting Mihnea to write the rest of the map!)
I'm not sure what happens if the idle switch is closed but the throttle is open, maybe the boost will be reduced.

sounds plausible... I'll double check the sensor tomorrow and make sure there's nothing obvious. If that doesn't fix it, i'll try a standard ECU and see if its the map. I dont know anything about the map that's in it which worries me a little...i like to know these things!

as always, thanks for your help!

[willg54]

just read through this:

http://forums.quattroworld.com/s4s6/msgs/20405.phtml

and it seems that this could be what's happening and ties in with the only fault code i've got!

[willg54]

i did an oil and plug change this morning and found a couple of plugs had come slightly loose which couldn't have been helping things...

I've adjusted the throttle cable with a bit more slack as it wasn't quite engaging the closed throttle switch so thats a definite improvement.

as for any other observations...i couldnt see anything.

I have a spare re-circ valve and n75 in my box of bits which might be tried if things dont clear up

[willg54]

whilst doing a spanner check tonight, i found the jubilee clip from the turbo bleed to n75 valve was loose...may aswell have not been there. im guessing that could have been causing me many issues!

[Drummer87]

Have you tried discounting the n75 an driving and if the problems still there or not?? See if it is defo boost related. Did that to mine and some slight niggles still. Know off topic so I'm thinking spark or coil

[willg54]

disconnecting the n75 will just give me mechanical boost i think, so not much point in doing that.

I'm going to take her for a drive tonight and see if the problems gone...otherwise im trying a 2nd n75 valve tomorrow...then i'll just have to live with a small problem as i'm off on wednesday!

[Drummer87]

But if you can drive the car faultless with n75 off then you know it ain't mechanical. Maybe your wastegate has packed in dumping too early on over boost and then the over boost protection in the ecu has kicked in

[willg54]

the symptoms i have are that the car dumps boost to mech boost for a short period, then normal operation resumes. disconnecting the n75 will just give this permanently and not really give any clues as to whats going wrong.

the fact it's intermittent i reckon means that it's not the mechanical boosting parts failing, its something that controls the system otherwise the loss would be permanent too and there would be more severe boost loss.

the boost system can hold the boost 95% of the time even with overboost. its just the odd time its dumping it.

[Drummer87]

Guessing you checked all hoses for clamps and splits. Done a boost test, vag com your car??

Strange what it's doing. Don't think a new n75 will sort it. Depends if yours currently is duff. Have you stripped your wastegate

[willg54]

Guessing you checked all hoses for clamps and splits. Done a boost test, vag com your car??

Strange what it's doing. Don't think a new n75 will sort it. Depends if yours currently is duff. Have you stripped your wastegate

all hoses are new, clamps are tight. i very much doubt this is a boost leak problem.

only code i got was throttle sensor which i think was idle error as it wasn't quite hitting the switch (now fixed)

n75 might sort it if thats the problem...which is top of my list currently.

Wastegate has been apart and diaphragm is perfect

[Drummer87]

Did you test the n75 so you can hear it clicking?? Whilst diagnosing. Have you checked the hose to the ecu??