hawku8

been a mechanic for 30 years but this thing is kicking my butt. timing belt, plugs, wires, fuel pressure all eliminated as possibilities. wont stay running cold and acts like the exhaust is plugged as it wont let u accelerate but if u can get it all the way up to operating temp it purrs like a kitten and revs up fine except a surge/hunt for about 30 secs when shifted to drive. cold prob goes away with the maf unplugged but replacement with known good changed nothing. compression is 160-165 dry and 225-250 wet. thinking a computer but no way to verify with cheap scanner on hand. 2nd question - should tps be 20% at idle? any ideas or anyone with previous experience with similar would be greatly appreciated.

AzTumbleweed

Have you tested the vacuum when it's cold? A low vacuum reading could mean the exhaust is clogged. I don't know why it would go away though after warm-up. Has the fuel filter been changed? Are you getting a check engine light?

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Nevada Tumbleweed

mightymoose_22

As I was commenting yesterday in another thread, it seems just about every time I hear the word "surge" I think of the IAC, and it usually turns out to be the culprit.

It sounds like you have covered most everything... I think if I were in your position I would plug all the vacuum ports and see where I stand. If you suspect plugged exhaust, go ahead and disconnect the manifold as well... gonna be noisy, but step by step you can eliminate more possibilities.

However, if you haven't replaced the IAC anytime in recent memory, take the thing off and try to clean it up a bit then check your symptoms. I am not aware of a way to test it, but if it is causing problems, having cleaned the thing out with some kind of spray to get the gook out should cause some kind of change. If it is telling the computer that there is more or less air than there actually is then that might account for the problem...

Doesn't sound like timing... runs fine at temp, so I doubt fuel.... and probably not exhaust. IAC is only thing making sense to me... its where I would start.

hawku8

tried known good iac from 98 donor escort with no change vaccum at 2000 rpm's (when u can get it that high) is 22" and 20" at idle so I am discounting plugged exhaust. my donor car with exact same eng has ecu JJJ3 and my prob child has ecu LLL2. anyone know if the ecu's are compatible enough for swap for test?

hawku8

mystery solved. I did not want to risk the ECU from the kg donor veh by plugging it into the prob veh but I decided to plug the ECU from prob veh into donor veh and installed same symptoms exactly into it. removed cover from ECU and one of the legs of one of the EPROM's is coroded all the way into the circuit board. final diagnosis faulty ECU. thx for the input all. Will confirm with a message after repair which is the only time we can be certain anymore, lol.

zzyzzx2

Wow! Pics please! Seriously, I'd like to see that. Were other pins corroded as well?

mightymoose_22

Sounds like you solved it.

If not, you can always try kicking it. That has a low probability of fixing anything, but I usually feel better after I try that.

hawku8

New ECU finally came in and the car purrs like a kitten. was not able to get photos of the corrosion as the damage is so tiny my camera would laugh at me if I tried. Plugged heater case vent is what I believe caused the corosion. problem solved is all I care about.

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Sincerely Hawk GM tech/Engineer

mightymoose_22

Hooray! I love happy endings