Oscillating Idle Like Clockwork on 94 Galant
 

I have a 1994 Mitsubishi Galant (2.4 liter 4 cylinder) which has recently developed an idle problem. Once the engine is warmed up, the idle will oscillate between 1200 and 1800 rpm like clockwork every two seconds or so. The car has about 192 K on it, but has been maintained well over the years; most recently in December it received a new clutch, timing belt, full tuneup, valve cover gasket, all service belts and driver's side engine mount. The "Check Engine Light" usually comes on after warming up, might then turn off, and might come on again, but it's been doing that for at least the last four years. And the SRS light has been on ever since I can remember. My mechanic started by replacing the temperature sensor on the upper front part of the engine, but this had absolutely no effect. His follow-on suggestion is to replace a device on the upper firewall which is tied into the vacuum system. I don't know if this course will fix the problem. I thought perhaps someone out there may have encountered this rather specific symptom before. I can drive the car fairly normally once I exceed the idle rpms, but the nagging concern is whether or not this might be harmful in the long run. Thanks.

Ok, so now we're looking at the IAC motor and/or the MAF meter. Anyone out there with any experience in this particular region of the machine? If you do have knowledge and are willing to share it... well, quite frankly, I think you're destined for greatness.