I've got a 96 blazer with about 150,000 on it and its just started having a strange problem. When I drive it it will mis really bad when I'm crusing at part throttle but when I step down hard on the gas it will smoth out and run right again for a little bit. It seems to idle ok, also it happens more when its wet/raining/humid so I'm thinking it's an electrical issue but I'm not sure where to start looking. I know its not the cap, rotor, plugs or wires, I've changed them out twice trying to solve this already.

 

You may want to check your TPS sensor with a volt meter by tapping into the wires on it (I think I covered this somewhere before). With the key on, take note of the voltage value on the TPS signal wire to the PCM. At rest, it should be ~0.5VDC. At WOT (wide open throttle), it should be ~4.5VDC. It should be a smooth ramp from at rest to WOT. If at any point in the travel of the throttle body it drops to zero, you have a faulty TPS sensor. I have seen this happen in a few cases where the vehicle was predominantly driven at one consistant speed with very slight variation in pedal position to maintain that speed. This resulted in a worn spot on the variable resistor grid inside of the TPS sensor.

Another preventative maintenance item to do would be cleaning the MAF sensor. There are several posts on how to do this in various areas of the forum. If you have any questions, just post up here.

 

Thanks, for the quick response, I'll check the TPS this weekend!

 

Cap & Rotor

 

I know its not the cap and rotor, as I said in the first post the cap, rotor, plugs and wires have all been replaced twice already with no change in behavior. For the cap and rotor to be bad I would have had to have gotten 3 bad sets (the old set that I first got the problem with plus two brand new sets). I have eliminated these as a problem and am looking for other things to check.

 

and if you didn't get GM parts or eqivalent all the new sets in the world wont fix the problem. These engines require lots of spark, and cheap electrical parts dont cut it. Took me 4 months of chasing my butt and a $160 at the dealer to learn that lesson. I upgraded to a better cap, rotor, and plug wires and my P0300 went away as fast as it came.