Ok im stumped, son has a 92 gmc c1500 tbi 5.7l and it idles fine but when driving between roughly 1200 rpms to 1800rpms it surges unless you let off gas and gradually accelerate. I did a vacuum check, fuel pressure test, fuel filter, new injectors, o2, spark plugs and wires, still the same thing? Any ideas what the problem is?

 

Likely a bad TPS (throttle position sensor).

 

1) What’s your definition of “surging”? Do you mean the engine acts like it cuts out for a moment; or is it more like the transmission slips out of gear and the engine starts revving? If the latter, is it an auto or manual transmission?

2) Is it ONLY when driving, or can you duplicate the stumble sitting in park/neutral while revving the engine? What about sitting in gear and revving (brake stand)?

3) Is the service engine soon light on? If so, have you checked the diagnostic codes, and what are they?

4) Of the diagnostic tests you have done, have you performed any of them while the surging occurs?