Car is a 1992 Corrado with the OBD I. Idle will intermittently go nuts (up from normal to switching between 1500rpm and 2500rpm like a metronome). Tried driving it, the thing bucks like a horse when the problem kicks in. High load at low rpm seems to trigger the problem. I unplugged the O2 sensor, the car runs very rich at the same frequency as the bucking, but is at least drivable now that I can clear the rich mixture with a simple punch of the clutch & a pop on the throttle to about 3Krpm at the same time. On the open road, not much of a problem (in fact, the problem has not occurred at highway speeds). At an uphill stoplight, it's one that makes me sweat.
I'm thinking that since the ECU has no input from the O2 sensor, it's not trying to "fix" the mixture, and that's what makes the car drivable. I'm just wondering what causes the rich mixture to begin with. ISV was swapped with a known good one, no difference. I should admit, I broke one of the fittings on the little air bellows that connects to the ISV (was going to disconnect everything and clean it out), and the replacement is from a Mk.3 Golf. Don't know if that makes a difference or not..
Anyway, I'm looking for suggestions. At the moment, I suspect the MAF hotwire going bad (connections have been cleaned).
