hi all, i have a 96 gmc with a 5.7 vortec and as of late it don;t idle right, its ok in park, but once in gear, it jumps to about 1100 rpm then slowly comes down to about 800 rpm, until you drive over 30 mph then the idle will only fall to about 1200 rpm. i replaced the iac valve and tps with new ones, i searched for vac leaks and found none, i have put new plugs, cap & rotor on, with no change in idle. no lights on the dash, no stored codes. ***? it was somewhat tollerable on dry roads but now the roads are covered in ice so it really sucks now. any input is greatly apprecieated and thanx in advance!
runs like it has too much fuel
- Thread starter blumax
- Start date
NJKen
is a daddy!
If you have the engine with the black plastic upper manifold you are probably inline for a manifold gasket (usually lower manifold to heads) due to GMs 8 bolt intake and plastic gasket. Do you have a check engine light on by any chance?
Ken
Ken
sle2115
NRA LIFE MEMBER
Coolant temperature sensor will do some weird things too! Dad's 4.3 drowned itself, unplugged it and it would start and run well as well as running like a top at idle. Replaced it and all is well.
i was poking around at it yesterday and i pulled the oil fill cap off to see if there was some blowby and there was a a lot of suction, so i pulled the pcv out and it hardly changed, then i checked the plugs and #4 had oil on it, the rest looked good. so i think it must be the intake gasket.-scott
NJKen
is a daddy!
It probably will. That is an all too common problem with those things. I have 3 of those engines in my fleet and they have all been done once and one done twice. Let us know how she runs now.
Ken
Ken
Goofyexponent
Mentally Unstable..
I agree that the intake gaskets are shot! We had a 1997 at the concrete plant, and this is where I learned the Vortec engines were FAMOUS for this happening.
NJKen
is a daddy!
They sure are. You probly also learned that dexcool plus engine oil makes some of the stickest nastiest stuff on earth. It likes to wreck all the lifters too.
Ken
alls well in vortec land now, runs like it did with 150,000 miles, idles at 600 rpm, nice and smooth. #1, #3, #2 & #4 intake ports were full of the nasty sticky so this may have been going on for a little longer than i thought. i just can't believe some engineer thought this design was a good idea to put into production, whoever came up with 2 bolts in each corner and plastic gaskets needs a real good swift kick in the nuts and should have to fix a thousand of these in a row! oh-well, wifes happy, its her truck!-scott
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