200 might be sick again, then again

[Tom Winter]

Geraint:

Yes, low octane gas could make your car do this, but then the light should
stay off once the high test stuff is put in.

Other listers have come up with very good advice, but here is anther thing
to look at. It's fast and simple, although I think you'd be able to pull the
code for this. But if a wire is merely loose or has an intermittent bad
connection, then maybe not.

In a 5000 tqa I owned the air temp sensor in the intercooler had a loose
wire. Under certain loads, the CEL would come on. The the car was an 87 with
an IA stage I chip and wastegate spring. The car drove great, but the light
would come on and go off, etc, etc. Much like your symptoms. I ended up
being able to pull the code.

It's pretty easy to pull the rubber boot off the sensor and inspect the
wiring. I ended up having to clean up mine (covered in oil) and was able to
re-attach the wires and solder them. The fix was a bit rigged, but it lasted
for 3 years until the car was sold.

Good luck

Tom 
'95 S6 avant