99 Sierra Hot start idle problems

Aspired · February 12, 2006

I have a 1999 GMC Sierra with the 5.3L Vortek

Problem: When I have run the truck to say work or the store then shut it off (warm engine) then come back and start it like 5 minutes later and it starts but the idle drop almost to zero RPM's and back up ten back down fluctuation bad.

If i hit the gas it straightens it out (the idle) but it seems to be getting worse, before it started right up now it is cranking for a little while then iddling like crap.

I had the engine light come on - i read the code and it said I had a bad purge valve solenoid - I put a new one in for $75 buck and cleared the code. didn't fix it but the engine light is off now.

I think it maybe a throtle body sensor or fuel pump problem - anyone can help me I would appreciate it dearly before I start replacing more parts that may not need it.

-Aspired

RyanZ71 · February 12, 2006

I would try cleaning the throttle body first, just get some TB spray and clean the hell out of it, I did it on my 99 and it solved my rough idle problems, though mine were not as extreme as yours.

Aspired · February 15, 2006

I would try cleaning the throttle body first, just get some TB spray and clean the hell out of it, I did it on my 99 and it solved my rough idle problems, though mine were not as extreme as yours.

<{POST_SNAPBACK}>

I did clean the throttle body, even before I put on the new purge valve solenoid, was very black inside there but the old guy who owned it before me barely drove it and I am sure he did never got on it.

I am going to try to take it apart a bit further and really give the TB a good polish, it might still have some junk in there this weekend and test the sensor/price a replacement.

Thanks for the reply

Aspired · March 1, 2006

I would try cleaning the throttle body first, just get some TB spray and clean the hell out of it, I did it on my 99 and it solved my rough idle problems, though mine were not as extreme as yours.

<{POST_SNAPBACK}>

I did clean the throttle body, even before I put on the new purge valve solenoid, was very black inside there but the old guy who owned it before me barely drove it and I am sure he did never got on it.

I am going to try to take it apart a bit further and really give the TB a good polish, it might still have some junk in there this weekend and test the sensor/price a replacement.

Thanks for the reply

<{POST_SNAPBACK}>

ok I figured it out I think for now anyways. It seems to have been a tps (throttle position sensor) on the throttle body. Cheap part that like everything is kinda hard to get at unless you have a good set of tools, which I do.

It seems to work fin now but we will see if it comes back

-Aspired

BRZ71 · March 1, 2006

I have a friend w/ a 87 F150, his was doing the same thing for a few weeks while we changed everything under the hood. It was the TPS sensor too. I was also going to suggest the idle air control valve, or EGR.

Aspired · April 8, 2006

I guess I seem to have been wrong.

It seemed to work fine for about 3 days now it is acting up just like before - truthfully I don't drive it that much with gas prices so high unless I need to haul something. Which means it is usually a cold motor when I start it and it works fine then, just problems when the motor is warm.

I am going to test my fuel pressure next, to hopefully eliminate a possible fuel pump or injector failure.

I will also throw on a new EGR valve.

Any more help would be appreciated.

Aspired

BrianH323 · April 8, 2006

Extended cranking and rough running when it first starts up is the fuel pressure regulator alot of times. Take off the vacuum line that goes to it, is it wet?

Brian