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90's Volvo S80 does a "surge" while idling

It’s got 120K miles on it. It’s well maintained. But lately we’ve noticed the car “surges” while idling - either at a light or shortly after start-up. If you don’t have your foot firmly planted on the brake, it could potentially hit the car in front of you (at a light) or run into something.

Has anyone else encountered this, and if so, what was the outcome?

My vote is for a vacuum leak/idle air control valve. Have it checked out, if it is vacuum it should be a relatively inexpensive fix.

Ditto. A vacuum leak is the most likely suspect, and it is easy to fix. If that is to no avail, then the IAC may be gummed up.

Took the S80 to the mechanic and he says that the PCV system has become gummed up with carbon. Apparently this also causes problems for the Electronic Throttle Module (ETM). He referred to Technical Service Bulletins indicating that this problem is common in Volvos. The cost to fix is around $2,000!!!

Get another opinion. I did a head gasket on my cousin’s S70, and noticed her PCV system was in bad shape. Most of the hoses had cracks and breaks, and the system simply wasn’t working. Vacuum leaks all over. A few new hoses, and the system was back in shape. The only thing that may be expensive is a module on the front of the engine under the intake manifold. It is a box that the PCV hose from the engine gos in, and two hoses come out, one small vacuum line and a larger breather hose to the intake. I’ll bet just replacing the hoses will stop the surging. If the box is fouled up, check with some salvage yards. Far cheaper than $2000.