2002 blazer 4.3 idles rough 500rpm. runs smooth till you hit 50 - 55 mph it shifts hard when you give it more gas. Pulling up DTC codes for mass air sensor, crank sensor, cam sensor, knock sensor checked plugs autolite gapped at 75 Replaced plugs did a water test on plug wires -passed still ran rough at same speeds still pulling same codes! Solution pulled crank sensor cleaned, disconnected battery ground cleaned cleaned Mass Air Sensor with CRC, Cleaned Throttle Body Both of these were dirty . Test drive idles at 750 smooth no more miss fires climbing hills cruises at 80mph with plenty of peddle left. No more codes pulling up Sure glad i didnt replace any sensors i hope this helps somebody i guess you need to find why the codes are pulling up such a simple solution!

 

Why exactly did you gap the plugs a .075? .060 is the spec they should be at.

 

Sounds like the cleaning of the sensors/throttle body are what ultimately fixed it.

 

Thanks for the info, I also have a rough Idle at 500rpm too. The throttle body was full of gunk, cleaned it up and things are a little better. Still stuttering a little, going to give cleaning the crankshaft sensor a try. Its pretty badly gunked itself from an oil leak i can't seem to locate. Almost looks like the lines from the oil filter are leaking... Has a little stutter between 1600 and 1900 rpms too. Is cleaning the MAF sensor as easy as buying some crc and spraying it down?? I know where it is but I have never removed the sensor, not quite sure what it looks like on the inside.

 

Glad you got your truck fixed. You did not have to do a crankshaft relearn after you cleaned the crank sensor? F.Y.I Keep in mind for the future that all those sensors have one thing in common which is vref and buy you unplugging and cleaning things you might have fixed a wire that is not making a good connection,to set all of them codes because they are dirty is very unlikely, I am not trying to burst your bubble this is just some info in case it happens again.