90 s10 4X4 weird idle..vacuum leak??? :-(

[ballinjefe22]

first of all...i wish i could make that face A LOT bigger. haha
got a couple problems

1985 s10(originally 2.8) with a 1990 4.3 TBI that i swapped in.... i drove it home about 20 miles from where it was sitting, and drove fine with no problems. drove it a couple other times just around the neighborhood with no problems. then out of the blue, it decided to die at a stop sign. and the idle was just really messed up. SOMETIMES when the engine gets warm, the idle will rock back and forth like it has a really bad vacuum leak. it will go up to about 1200rpm and then all the way down to just about nothing, so low that the engine rocks and knocks. i have driven it around a few other times, and sometimes it does it, other times it doesnt. i checked every vacuum line from the TBI unit. capped off the vacuum line that used to run to the cruise control unit. and capped off the vacuum line that used to run to the vacuum canister. i checked a few different ways to see if it was the intake manifold gasket, and have decided thats not it. i cleaned the IAC, checked and rechecked the timing, changed the plugs/cap/rotor. i dont know where to go from here. any ideas at all? please help...if anymore info is needed, im sure i have it. i really wanna go camping with it sometime soon. haha thanks in advance.

[MT-2500]

Check egr valve for sticking.
Give us your engine vacuum readings at idle and at 2K rpm.
When it is running good and when it is acting up.

[ballinjefe22]

i tried to get the egr valve off but those bolts just do not wanna come out... i gotta get a vacuum gauge tomorrow to check out the vacuum. just outta curiousity, why at 2k? i had a couple guys at work tellin me it could be the fuel pump? any thoughts? thanks again

[MT-2500]

Proper testing will tell you the problem.
The idle and 2K is a good test point.
And the reading at them two RPM will thell you if the exhaust system is restricted.
Lower vacuum at 2K over idle shows exhaust system restriction.
A fuel pressure gauge will tell the fuel pressure.
A vacuum gauge will give you the vacuum readings.
Which tell you a lot about engine running.
If you can not remove egr valve unplug it when engine is running good and see if it acts up again.
If not suspect EGR valve.
Vacuum gauge readings will show a stuck egr valve ,late timing and bad valve and engine miss. restricted exhaust and a lot of other stuff.
Vacuum readings is a poor man,s and a good mechanics best diagnostic tool.
And
A 5 $ vacuum gauge gives you more info for your money that any other tool.
One of the first and best diagnostic tools made.
Get one and learn how to use it.
And post back your vacuum readings.
Good Luck
MT

[ballinjefe22]

well.. i think i wasted some peoples time. i had a mechanic that i met from work come check the vacuum for me. he said it was fine. i let it run til it started to act up, and took the egr valve vac. line off and that didnt change anything. so i ran to work and get a fuel pump. ($40) took about 30 minutes to swap out.... drove it around and let it run for about 45 minutes with no problems. hopefully that was it. thanks for the insight though. may not have been the problem this time, but may be good to know for future reference. thanks again for the help.

[MT-2500]

Proper testing time is never a waste of time or money.
Good Luck
MT