Mazda Repair: 93 626 dies, engine combustion, cylinder compression

Question
I have a 1993 626 with 2.5 ltr. V6 automatic. Car has 73,000 miles. It will stumble occasionally, but the worst part is when it warms up, it will not rev above 2600 rpm without shutting off. When this happens it does not completely shut off every time. Sometimes it will diesel and knock but register about 200 RPM on the tach. If the car sits for a few minutes it will start up again, but usually the first couple of tries it revs and dies immediately. Your dealing with a cave man who loves carburetors and points (for some background)but this sounds like an ignition problem to me. I had the same problem with this car four years ago and was told it was the distributor (coil) and the whole unit needed to be replaced as they are not serviceable. Was that a line of crap or is that the case? Any advise or suggestions would be greatly appreciated. This has been a very reliable car except for this re-occuring problem. This car gets roughly 4-5 thousand miles put on it in a year. I can't believe that the distributor that was installed would fail in approximately 15-20K. Thanks in advance....Gery.  

Answer
Hi gery .thanks for asking.
I really dont think it would be an ignition problem---with the deiseling affect--- These engines where famouse for buning out valves. when a valve is burnt out there will be thinner parts of the valve exposed to engine combustion, these thinner parts of the valves will glow red hot when the eninge is running, when you shut the eninge off because it is electronically ciontrolled the igintion coil stops feeding right away, but the red hot part of the valve will burn the extra fuel in the intake manifold coming into the cylinder--- giving you the deisel affect. This may be the problem with your running condition. the first thing I would do with this vehicle is do a cylinder compression check and a power balance test if possible. follow me up on this and let me know what you find
Good luck
Chris P