Limp Mode

Hi all! This is my first post (just joined yesterday). This is a great website and have used it often. Thanks for everyones help!!

So here is my problem (yet another limp mode problem):
My 2000 Beetle TDI has been in and out of limp mode for sometime. I've looked at the majority of the posts including Canadian Grizzly. I helped a friend change the turbo on his 2000 Jetta TDI and he gave me his old turbo. I had it overhauled and the actuator repaired by Turboworks. I installed this turbo, cleaned the intake, EGR, pipes, intercooler and snow screen. I changed almost all the vacuum hoses. I recently purchased a Ross Tech Vag Com. The error code is 17964 Charge Pressure Control - Negative Deviation P1556-35-10 Intermittent. I did check the operation of the N75 using the Vag Com (OK).

If the N75 works using the Vag Com, can I assume the vacuum system is ok??
If the MAF sensor is bad, will it throw a code??

Anyone have any ideas??

Thanks

I had the same problem on mine even after brand new turbo. I changed the MAF and made no difference. In the end I changed the N75 and was an instant cure. from memory the diag did show up some pressure error when I was getting limp mode.

The N75 functioning does not ensure that your vac system is good. You could still have a vac leak.

Might take a look thru these forums or on youtube for the VNT actuator test and see if perhaps you have a sticky actuator rod, actuator arm, or faulty vacuum actuator.

few years ago (at around the 170K mark) I started experiencing random limp. I replaced various things, was not adept at diagnosing down to the specific component. (it's difficult to do with an intermittent problem.) In my case the problem turned out to be the N75. Not saying that's always going to be the case, just my 0.02.

Check your IAT sensor, if that is OK, do a smoke test on your intake system. I had the same problem.