'96 5.7 vortec random idle changes

[jim mcg]

random..at start up..1500.rpm.then will drop to 800..rpm.stop light may jump back up to 1000 rpm then random all through daily drive...??

 

[Schurkey]

Connect a scan tool, look at the data stream. I'd be wanting to know the coolant temp, the commanded idle speed, the actual idle speed, the IAC position, the O2 sensor readings, short- and long-term fuel trim, and the MAP sensor readings at minimum.

"Codes" if there are any, may be useful also.

When these were new, intake gasket failure was pretty common. You could easily have a vacuum leak.

 

[mrvsfriend]

My guess is throttle position sensor. They're cheap and you can swap it out in the auto parts store parking lot.

 

[Schurkey]

My guess

Why guess? Proper diagnosis with a scan tool would tell the tale.

 

[jim mcg]

no codes...may have to guess ?? replaced entire rebuild 6 months ago..would hope intake gasket..ok...just started...and it goes away for maybe 1000 miles then comes back random...hwy drive..seems to help. hmmmm

 

[Schurkey]

no codes...may have to guess ??

Stop LOOKING for codes, start looking at the data stream.

Guessing works...sometimes. Proper diagnosis works all the time.