i have a stock l98
i have been chasing a rough idle for weeks now .
here are the symptoms .
when you first start the car it stalls, try it again it will run but it runs rough and the motor shakes the whole car . for about the first 5min of driving the car smokes , seems like oil smoke (blueish) and the exhaust smells funky . if you drive it and let it warm up it gets alot better and runs pretty good (but still has funky smelling exhaust) .

this is what i have done so far ,

checked codes - none .
tested ALL sensor's according to GM shop manual - all good .
tested fuel pressure - good .
tested plugs/wires/cap/rotor - good .
hooked up to a snap on scanner - all seemed within range (im no expert with 1 and was on limited time with it) .
used carb cleaner to check for vacuum leaks - found none .

here are things that have been replaced within the last yr .
injectors
fuel pressure regulator
IAC
CTS
EGR valve

this seemed to happen all of a sudden out of nowhere and i am running out of ideas , what would you do next ?

 

i would check thoroughly for vacuum leaks, they can usually cause idle issues.

you mentioned that it smelled like oil... are you loosing any oil?

is the smoke coming from the exhaust, or could it be oil dripping off of somewhere and burning on something hot (maybe headers)?

 

check all of the vaccuum lines especially the (TB to EGR solenoid line) they melt first. and check for vacuum leaks around the manifold, etc. spray some starting fluid around suspected leak areas, and if/when you find it put some sensor safe rtv and let it cure for 24 hours. just a start. also try a vacuum guage and try to find it that way...
good luck and god speed
Goodfella

 

never said i smelled oil , and yes it is smoking from the exhaust .

tried that as mentioned ..

 

so if its not oil then you are looking at fuel.
maybe you have an injector stuck open.
or at least INTERMITTENTLY

thats really the only other thing that would cause smoke.
and cause the car to run rough

 

Have your cooling system pressure tested. Sounds bad, but you may have popped a head gasket. Pressure testing and checking by a good mechanic will tell you. Does the exhaust smell sorta sweet?

 

Does it run ok after it warms up?I would pull the plugs anyway and look at them. Sounds like valve seals letting oil in or popped head gasket- cracked head.

 

ya it runs pretty good after it warms up . the exist does not smell sweet and i have not noticed any coolant loss .

 

I would pull the plus and run a compression check.

 

sorry my error i misread. i falsly put together the "seems like oil" and "smells funky" .


i would definitely do the compression test, and maybe a leakdown if you have the tools to do so.

 

If you run it with the rad cap off (starts it cold), does the coolant seem to have alot of bubbles come up? Sometimes a leaking (not blown) head gasket will not be bad enough to leak fluid, but can leak compression from the cylinder into the cooling system.