Recently bought a 93 Legacy wagon off Craigslist for my father to commute to work out of town. It runs good and is used to commute 250mi's a week (highway drive 125mi there & 125mi back). I check it out every weekend when he gets back.
THE MAIN issue is it backfires thru intake at startup & the idle is high, only when engine is cold! After it warms up it runs better & idles fine. It had the Bosch 4 prong platinum spark plugs, runs better with copper NGK's, but still backfiring. I cleaned the PVC vavle, MAF sensor, IACV, & throttle body also. Had the exhaust checked out & they replaced 1 of the cats but not sure if they really checked EVERYTHING out. Previous owner had replaced the plugs/wires & air filter. I've researched this & came across a few possibilities but the car runs fine once warmed up.
coolant temp sensor could be failing-dumping too much fuel at warm up. Timing belt could have jumped a tooth. Exhaust leak near the head or at the Y-pipe allowing air in & then closing when warmed up. Low or uneven compression. These are some of the problems that I read can cause a backfire but the car runs really nice once warmed up.
Another issue is the speedo doesn't work. Check engine light is on for Vehicle Speed Sensor. And the POWER light for the trans blinks when you turn the key on. I figure that the tranny Control Unit senses the VSS & is why power light blinks. So does this mean the Tranny is in a "SAFE MODE" not performing at its best because the computer sensed a problem? It feels like it could have more acceleration & performance is what im getting at.
Any helpful suggestions, comments, questions or information is highly appreciated! THANKS.