1999 1.8T power loss

[jdhartman24]

I'm sure everyone is sick of seeing the same topic, but I've read every previous topic I can find, tried some of the fixes, and still no luck! Here is the problem. I have a 1999 1.8T. Several months ago I began experiencing an occasional boost problem. Sometimes the car runs at 8psi, but other times it runs and/or drops to 5psi. Here are some of the things I have tried with no long term fix.
1. replaced N75 valve(several years ago, different issue)
2. replaced MAF sensor, no change
3. checked all hoses, clamps etc. I found a split in the mass air meter hose, replaced hose
4. With hose off, reached into turbo and spun vanes around with no resistance.
5. had car @service for engine light on(P0420 low cat efficiency) cat replaced

The car will run at full boost 50% of the time and 5psi the other 50%. During the same trip it starts with full boost, then drops, or does the opposite low boost to normal boost.
HELP!!!!

[JayB5UK]

Have you tried changing the standard dump-valve, I forget what they call it now, but an uprated standard one from a 225bhp Audi TT is pretty cheap and well up to the job.

Another secret is to remove the plug for the MAF and coat all the small sockets of the plug with Dielectric Grease, work it on and off a handful of times then run the car. You should notice a difference, when I did my A4 it was much better and it erridicated the feeling of it running more boost some times than others you mention. It is well documented on the U.S. forums, have done it to my TDi also and it made a difference. The thing it does is ensure a constant good connection to the MAF. It's probably worth doing first, the grease will cost about £5.00 !

Good luck