I have a 2000 Blazer with 131000 miles. The engine runs great except at low RPM. If the engine is running below 1000 RPM it surges but once the RPM goes above 1000 it runs fine. Could this be a problem with the MAP or MAF sensor? Also, this does not happen 100% of the time but at least 80% of the time. Thanks for any suggestions

 

4.3 engine. No codes

 

There are quite a few potential causes of a surging/hunting issue:

Vacuum leak
EGR valve/passages
IAC
ECT
Knock sensor
Air in coolant
MAF
MAP
Fuel pressure/delivery (pump, injectors, regulator, filters)
Exhaust restriction/cat
Crank sensor
Power steering position sensor
TPS
Ignition problems (and all components)
PVC
...

So as you can see, guessing and throwing parts at the problem can get frustrating and expensive. The trick is to narrow things down.

Does the truck have any other problems?

Any work performed just before the problem?

Do you have a scanner with live data and misfire counter capability?

I would start with the fuel pressure sticky, system voltages at idle and higher rpm's, looking for a vacuum leak, the IAC, and clean the EGR valve if you have one. If you have a capable scanner then we can do more evaluation looking for clues.

All the fun is in the journey, or so I'm told.

George