I have a 93 s4. 144Kmiles. Been running like a champ with boost to 22psi. Recently boost drops to 6psi limp mode at 5000rpm. Doesn't matter how much boost was on when it hits 5000 rpm. even with 10psi, it will drop to 6 at 5K. I can sit at 22 until to revs come up. Code is g40 intermittent short to plus. Plugs, POS, igniters, wires all check out. New Forge DV with no leak. Boost diaphragm ok.

I did have a disintegrated cam pos sensor connector, replaced with one from a known bad sensor. . I hate to spend $200 on a cam pos sensor unles i'm pretty sure it is bad. How do I check it?

Any other suggestions? I'm getting frustrated!

I have a 93 s4. 144Kmiles. Been running like a champ with boost to 22psi. Recently boost drops to 6psi limp mode at 5000rpm. Doesn't matter how much boost was on when it hits 5000 rpm. even with 10psi, it will drop to 6 at 5K. I can sit at 22 until to revs come up. Code is g40 intermittent short to plus. Plugs, POS, igniters, wires all check out. New Forge DV with no leak. Boost diaphragm ok.

I did have a disintegrated cam pos sensor connector, replaced with one from a known bad sensor. . I hate to spend $200 on a cam pos sensor unles i'm pretty sure it is bad. How do I check it?

Any other suggestions? I'm getting frustrated!

...type of problems you are having.

Thanks,

I replaced the N75 WGFV, No difference. I cleaned both old one and new one - no difference. The 5000 rpm is a clue above it, I fall back to 6 psi limp mode. As soon as I drop back below 5000, the boost takes a few seconds to recover. Drops off again at 5000 rpm.

Are you getting enough fuel? New filter, pump flowing ok?

Thanks for the suggestion. Just replaced filter and double-checked the pump. Good pressure and flow.

The boost drops from whatever it is at 5Krpm to 6psi (limp mode). Takes a few seconds to think, and kicks boost back in -- until it hits 5krpm again. It feels like a rev limiter...

Anybody have experience with an intermittent csp sensor?

Have you checked the TPS with a multimeter to see if the values are correct? They do go bad and can cause that kind of problem from my understanding. Also, is there any "bucking" when this happens? May need to tighten the connections on the moisture trap.

Here is some Throttle Position Switch (potentiometer) info from the FAQ:

http://forums.audiworld.com/showthread.php?p=18930483

Thanks guys. I think you put me onto the problem. The TPS checks ok except the max resistance with WOT is 2500 ohms, not the 3600 ohms in the Bentley manual. Is that a problem? I suspect not.

I have no voltage between pin 1 and 3. I have 5.0 between 1 1nd 2. I will look for the open in the wiring. I think it is pin 53 on the ecu.

Follow this link to the ECU pin-out in the FAQ:

http://forums.audiworld.com/showthread.php?p=18872781

It is pin 53, the list gives you the colour

Thanks. I got continuity between pin 53 on the ECU connector and pin 3 on the TPS. I still can't get 5V between pin 1 and pin 3 on the TPS. Wha is puzzling is I can see on the VAGcom TB angle changing.

I still loose boost over 6psi at 5000rpm to 6psi. I also get a few seconds of the Check Engine light. the DTC is an intermittent short to plus on the cam angle transducer

Imstsring to worry about the ECU...

What is the exact code?

Timing belt is a tooth off.