ZPmadA

My 86 944T is mostly stock except for an autothority MAF and Lindsey Racing mechanical boost controller set to stock PSI. The cone intake always had a nice sound of rushing air (almost like a blow off valve), but just recently I noticed what sounds to be compressor surge (fluttering after boost). I don't have an aftermarket blow-off valve on this car. I believe it has not had the Venturi delete upgrade. Could that be the problem? What else could cause compressor surge on a fairly stock 944T? Last time I checked my turbo doesn't have shaft play, and the intercooler pipes have a very light coating of oil (not dripping). I'd like to keep it that way so I'm not driving it until this is fixed.

944obscene

Oil in the pipes seems normal to me. You're gonna have a little in there. Never heard of these litle factory turbo's surging though. I'd check the bypass valve to see if it is functioning properly, as well as checking vacuum lines for cracks and bad connections.

ZPmadA

How do you check the bypass valve, and could that cause an occasional stumbling idle at startup?

gt37vgt

well one way is remove it and try hold water on one side and activate by sucking the small tube ..
it sounds like its the problem to be ..that is basicly the reason it exists.
I believe there are good stock looking billet ones on ebay as they are common fitment for a few audis and VW..

User 52121

Heh... thanks to this thread, I found a torn diaphragm in the bypass valve on my '86 951 I always noticed a little bit of compressor surge when under light/moderate acceleration, wasn't sure if it was "normal" or not (often stronger/stiffer bypass valves will surge a little on light acceleration so I didn't think anything of it.)

Decided to take a look, noticed it wouldn't hold vacuum. Pulled the valve out, had a look inside... and could see the rip. Doh!

Fortunately it looks like the same exact valve that comes on the VW 1.8T, and I've got my old stock one that used to be in my GTI I can use as a temporary replacement.