Rough idle, run rich, doesn't always start

Asked by Thomas Dec 25, 2018 at 12:06 PM about the 2001 GMC Sierra 1500 SLE Extended Cab SB

Question type: Maintenance & Repair

My truck runs rough at idle, doesn't always want to
start, and runs very rich. I've been slowly replacing
parts over the last year but none of the parts have
helped for very long..2001 sierra 5.3 with 155k on it

I've replaced ....
Fuel pump
Injectors
Fuel filter
Intake evap solenoid
Evap purge vent and hose
Fuel pressure regulator
Spark plugs
Plug wires
Air filter
Maf
Upstream o2 sensors
Also battery and alternator because they went bad
but I doubt that has anything to do with it
also have done a relearn

It will start... usually and runs fine once its past
1200rpm. As long as it's over 1200 it's perfectly
fine

1 Answer
42,415

Auto_Centric answered 5 years ago

Why do you think its running rich? do you have the fuel trim numbers? how about DTC codes. A simple test most people can do is connect a vacuum gauge (after the throttle body) for a direct manifold vacuum read look for a steady 18 to 22 in.-Hg of vacuum.

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