I have 2000 Honda Accord V6 with 140K miles and which is very well maintained and runs really nicely. However, every once in a while when I start it it would do some erratic rpm changes on idle and then stall. If I manage to get it moving despite rpm drops, it runs great and would not stall again. Also, if I leave it for a while (like 15 minutes) and then come back, it usually starts like nothing happened. For last 3 years it was doing it 3-5 times a year but now it started to happen more often.
I tried few times to raise idle RPM to 2K-4K and that ended up with CEL coming up. OBD codes would always be the same: P0300 (random misfire), P030X (Cylinder X misfire for X being any and all cylinders) and pending P1399.
In the Honda shop, when they saw those codes they said that according to procedure they need to replace fuel regulator and PCM and if it didn't help, injectors and some other things. Essentially they have no clue and I am reluctant to pay a lot of money just to experiment.
I recently replaced spark plugs and timing belt was replaced on schedule as well as all other maintenance requirements.
So I am getting desperate and wonder if anyone had similar symptoms or an idea of what may cause the problem.