Toyota Repair: 88 4Runner V6 - starting issues after warm, compression tests, toyota dealers

Question
Ted,
This question has stumped many Toyota dealers, I've found your website to be helpful in the past so I'm hoping you can help me diagnose a problem.

I have an 88 4Runner, 3.0 V6, just under 200K miles.  Every shop I've taken it too can't believe the condition it's in.  I'm the second owner and everything imagineable has been upkept.  So here's the challenge.  It runs great, starts all the time.  However, if the engine is warm and say I run into the store and come back out between 15-30 minutes the engine will act like it is flooded and sputter and die.  Or the rpms will bounce from like 500-800 and then when I put it in reverse or drive the engine will stall.  I have to rev the engine for a few seconds in order for it to stay at normal idle (800rpm).  Sometimes the Check Engine Light comes on, other times it doesn't.  The kicker is, I can almost set my clock to it, less than 15 minutes, it starts right back up, more than 30 minutes, starts right back up.  You wouldn't even know something was amiss.  It's not weather dependant, one time it happened during the spring and there was speculation it was just the change in gas from 10% ethanol based in winter to normal.  That doesn't seem to be the case.  The other indication that I think is important is that the mpg have dropped to 12 or 13 mpg.  I just had it in for the 200K tune up, the dealership said everything checked out.  A little oil on the spark plugs and since they were due I just had them change out the plugs.  Compression tests ranged from 160-180, they didn't recommend any fix.  They also checked the computer for any stored info on the Check Engine Light, nothing.  

One thing I did notice in the documentation from the previous owner (he wrote everything down) that last spark plug change he didn't change wires, just the plugs and distributor.  The dealership didn't indicate the wires needed to be changed.  It doesn't seem likely, but could that be part of the problem?

I have a good friend, at a distant Toyota Dealership, that thought perhaps it has something to do with the fuel pressure.  Another thought was a problem with the air flow sensor.  Wouldn't an air leak affect other times, like during normal driving?  I speculated fuel injectors, but it doesn't really fit the normal leaky fuel injector symtpoms?  It's a scary thing to start throwing money into ideas instead of an actual diagnosis.  Do you have any thoughts?

This is longer than most, but I figured I wanted to give you the best possible shot at helping me since I've run into a few dead ends at the places where I'd think for sure they would have seen this before.  I've taken it to two dealerships and two independant Toyota shops, no luck thus far.  Let me know if I can provide any more information that may help.

Luke

Answer
The only thing I can think of that may cause this problem is exessive carbon builtup on the back of the valves, this may cause fuel from the cold start injector and the injectors to soak up the fuel intil the carbon becomes saturated with fuel and then lets the fuel into the combustion chamber, it's kind of an educated guess so try to have the vlaves inspected it can be done without removing the cylinder heads but it requires a bore scope which can be inseted into the spark plug holes then the engine can be rotated until the valves open so the valve stem area can be inspected.