Chevrolet Repair: No power when warm, air fuel mixture, vacuum fluctuations

Question
Hello. I have a 1995 Chevy K1500 extended cab, 305, 5 spd. man. trans. with TBI and about 245K miles. When the truck is cold it runs fine. As it warms up it begins to lose power and sputters when accelerating. This remains the same once it is up to temp. I have replaced the TPS, MAP sensor, and coolant temp. sensor. I put a vacuum gauge on it (using the brake booster vacuum) and the gauge goes quickly back and forth between 17 and 22 at idle. I've read that this could mean bad valves. Could the valves be the problem or could it be something else? Also, the check engine light is off and there are no stored trouble codes. Thank you for your help.


Answer
Sorry it is taking me too long to answer today.  My son's Hockey team is in playoffs and game 5 of the first round is tomorrow!  I am the Coach, extra practice, busy shop, busy schedule, family man and no limit on questions keeps me busting my butt!!!

 Wow, nice homework you have done.  A quick bouncing vacuum reading (sharp fluctuations) indicates a cracked or 'v'd burnt valve.  If it is sputtering it is probably combustion flame igniting the air fuel mixture in the intake.  What you need to do is isolate the cylinder to see if this is the case.
 Do a compression test.  Find the cylinder that is lower than the rest (it may not be much but you will compare with the rest) and then bring that cylinder up to TDC and pressurize it with air.  You can use a blow gun or a compression gauge.  If you ahve a leakdown tester all the better but you probably don't.  Listen to the TBI and the tailpipe for air leakage and it will tell you what valve.


MOST IMPORTANT!

 Check the PCV valve.  I had one a few years ago I almost started tearing down a motor that was broken and causing vacuum fluctuations that imitated a valve problem. put your finger over it or use that hose as your vacuum source.

WAyne