Classic intercooler/intake hose problem. It could be the intercooler, but it could be one of the intake hoses. Even a SMALL hole can cause a total disaster when you're trying to boost. The real issue is that the computer adjusts everything to what the air flow meter says is coming into the engine. But what comes in slips out somewhere, so it isn't exactly the amount of air that the engine actually sees.

Although there are other potential issues, that's a classic intake air problem.

Once, I had to pick up a 740T from some other shop, where they couldn't figure out what on earth was it's problem. It was wrecked along the driver's side but on top of that, the thing ran like crap. I got the thing started and drove it for a while on surface streets with the boss following in another car.

Once we hit the highway, I couldn't even get to 55mph without the thing farting and popping. Broken intercooler hose I thought to myself. But we had looked at those before... they looked OK.

I called the boss, who was trailing me by about 1/4 mile (and I found out why). "This thing runs like sh#t!" is all I said when he answered.

He laughed. "Yeah? You should SMELL what it's like driving behind you! I've got f$#*in' gas all over my windshield!"

I finally got smart, stayed out of boost (tough on the hills) and we made it back. Weeks and weeks later, I FINALLY got around to looking for the intercooler hose problem, and there it was; a TINY hole near the throttle body. We had all but ruled it out because it was so invisible. The only sign was a little film of oil in an unusual spot, that led me to turn the underside of the hose up toward the light, where I could see the split.
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1992 940 wagon, 72k
make people envious; smile often.