I have a 2003 Subaru Forester that has been having starting/misfire issues for about 8-10 months at this point.
Last November, after making several short trips, I attempted to start the car. It started, but poorly, rumbling and shaking excessively with (what was later diagnosed as) a misfiring problem. I had it towed to a mechanic because it was undriveable at the time, but come morning the mechanic could find nothing wrong with it and could not duplicate the problem.
Fast forward a few months to February/March, it begins acting up again, and the Check Engine light has come on and stays on, reading a P0420 code. It begins having issues shifting gears, so I take it to the mechanic again, and they tell me that a lowered efficiency of even 5-10% in the catalytic converter can cause the P0420 to read and refer me to a transmission shop. I take my car to the transmission shop, and they fix a couple minor leaks, but say there is no real problem with the transmission. Instead, they say there is a misfiring problem. I drive it back to a mechanic -again-, and they diagnose a failed ignition coil and replace it. It’s fixed, finally, correct?
Incorrect. It is now mid-August, and my car has had three separate issues with starting over the past week. The first two times, the engine will crank and appear to start, but it won’t catch. The third time, it repeated the condition that initially happened last November: after several short trips, the engine cranks, tries to start, but fails, and instead rumbles and shakes excessively as if it’s misfiring. Fearing the worst, (the first time this happened, I tried to drive it home, and a small fire started under the car; I was not looking for a repeat) I had it towed again to a mechanic, and they spent two days with it and -once again- could not recreate the problem.
All I know so far: the starting trouble is intermittent. The battery and starter both test well and check out fine. The trouble comes most frequently after making several short trips (about 10-15 minutes, max, each time). It has no trouble starting first thing in the morning. The P0420 code is still there. Any suggestions?