My wife had the same problem with our 89 244 3K miles after we got it new. The original symptom was a low stalling idle, the dealer tweaked the throttle stop screw to correct the problem. A few days later, the idle was way too high and she called the dealership... their response was: "the computer is still adjusting to the new settings". Two days later, my wife was driving home on the freeway and the car kept speeding up. She had to smoke the brakes beyond oblivion to slow and stop the car before stopping short of a light pole on the exit ramp.

In short, the nut was not properly tightened on the set screw and the vibration made the set screw move upwards to the point of 4K RPMS in neutral. The dealer replaced every last piece of the the brakes and installed a new set screw and nut. After that, we got a free replacement radio, free oil changes, free driver seat foam inserts, along with free Volvo sunglasses and T-shirts!

In short, Volvo USA and the Dealer knew they had a serious liability problem!

jorrell
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92 245 317K miles, IPD'd to the hilt, 06 XC70, 00 Eclipse custom Turbo setup...currently being enjoyed!