2004 Starting when engine warm problem

figsys

My 2004 X Forester with 136,000 miles has a problem when starting and the engine is warm. Typically, driven at least 20-30 minutes then off for 10-20 minutes, on approximately 30% of the starts the engine briefly turns, "knocks" and dies with a clunk. Starts and runs typically on the next try or two. Does not occur if the car is not used for the day or overnight. Dealer could not diagnose the problem. A local mechanic duplicated this issue - found a possible issue with the timing belt and pressure sensor but addressing both did not improve the symptoms. The starter and AC compressor were replaced recently (just before starting issues) as well as crank pulley / crankshaft (after problems began - crank pulley separated). When engine starts, starts smoothly and runs as well as expected with the mileage.

Any ideas are appreciated

xwesx

Doesn't quite sound the same as the issue I used to have with my Outback. I assume that your car, too, does not post any codes when this happens?

The initial problem with my car (would start briefly, then die) was addressed by replacing the mass airflow sensor. However, I gave that MAS to a friend, who cleaned it and installed it in his car, and no problems for the duration. So, perhaps cleaning the MAS with an appropriate cleaner would be helpful?

The other (and more nagging) problem was that the car would often (started as occasional, became more frequent) refuse to start after being warm. I could literally crank it dead and it wouldn't start. However, try, wait 5 min, try, wait 5 min, and sooner or later it would start right up as if nothing were ever wrong. That ended up being, as best I can tell, a knock sensor or camshaft sensor issue. I replaced both at the same time (several years after the initial problem began) when the knock sensor failed while driving, causing the car to run terribly rough unless at very high RPM.