2001 Sierra 1500 Surging

blindman0v0 · February 14, 2015

Hello everyone, first time poster long time reader.

I have a 2001 GMC stepside with 4.3l auto that I bought 2 years ago. Love the truck,25mpg on my trips, you can't beat that.

Problem: Anything off idle and the engine runs erratic like it has a vacumm leak. New cap, rotor,plugs,plug wires and just threw a new TPS on it because it seemed like the likely culprit. Didn't change anything.

If I unplug the TPS, even with the new one, the engine runs perfect, no surging, but then on quick throttle close the engine dies. No codes on the computer. I just pulled the egr valve and cleaned it but still the same issue.

How can you unplug a TPS and the truck still runs and even runs better?

Thank You for any help.

8.1HD/ALLISON · February 14, 2015

Welcome! Have you tried cleaning the throttle body and idle air control? May also have faulty idle air control motor?

blindman0v0 · February 14, 2015

Welcome! Have you tried cleaning the throttle body and idle air control? May also have faulty idle air control motor?

Not yet but that idle air control solenoid was going to be my next check. But really that should cause a bad idling problem and mine idles great. Its just off idle where it starts sounding like its got a vacumm leak. Surges real bad and it causes some erratic shifting.

oldscsc · February 14, 2015

Might as well check fuel pressure as well.

If you have a fueling issue, the truck would run well when it needed a minimal amount fuel (i.e. idle) but run poorly when it needed additional fuel (acceleration).

blindman0v0 · February 17, 2015

Actually it runs fine at full throttle or idle, it just surges bad with light throttle. CHecked the vacuum today and its fine at 19". Pulled the Air control solenoid and cleaned it but it seemed to be working fine. Going to put a new cap,rotor and plug wires on it next. But I doubt thats it because I've never heard it backfire. And usually if the cap and rotor are getting bad or moisture has built up in the cap you get a distinct miss and this thing doesn't miss.

jonstreet · February 17, 2015

I did the Mass Air Flow MAF on my 4.8 and it helped but for awhile, I have a cold air filter on there no box or tubing just one slapped into place and it like to do almost die when I first hit the gas on a very cold start but it adjusts right after that first surge and then its fine. hope that helps a bit?

blindman0v0 · March 1, 2015

Problem solved. The guy before me had done a tuneup and had used one of the cheap aluminum contact type distributor caps. It was heavily oxidised and had created resistance which caused the rotor tip to burn and widen the gap. Good cap rotor and plug wires and it runs excellent know. Have never seen that problem cause surging before. Usually it causes missfires, backfires and poor power. But on mine it just caused a surge like a vacumm leak on anything above idle.