Hey guys this is my first post because my 1998 jimmy has me scratching my head for the first time in a while. First the cat converter has been one for a few months I just haven't been able to afford it but it just started doing this. At an idle, cold or warm, the idle will bump every 5 or 6 seconds. When I shift into any moving gear I can pop the throttle while on the brake and it shimmies really bad like its not keeping up with throttle response. And it also surges a little bit pulling hills or accelerating at low rpms. Its only getting 15mpg now. I've replaced fuel filter, TPS, maf sensor, and I ran system cleaner through it. Also there are no vacuum leaks I can find. Any help? My thoughts are fuel pump or a new catalytic...but an open mind would help more. Thanks.

 

95 Blazer 4.3 surges bad only after warm up. fuel pressure gauge goes from 52 psi to 60 psi rappedly.

 

Describe 'idle will bump every 5 or 6 seconds'. If it surges up and down at idle, that could mean a bad IAC/ Idle Air Control. That is a fairly easy and inexpensive thing to replace. Also check your MIL / CEL codes and post them here. You could have a lazy O2 sensor / poor gas mileage.

 

Damn , mine runs great and I only get 15 mpg.

 

yeah pretty normal