OK....Now I've been trying to beat this idle stumble for the last 3 months nearly. I have done every single test I can think of, replaced numerous componets, and racked my poor little brain. I have a miss/stumble at idle up to about 1500 rpm or so. It doesn't miss under load or while at a sub 1500 rpm cruise (like in 4th gear going 40 or so). Every now and then the idle "bumps", like the car is gonna die, but then returns to its irregular miss feeling. I bought an updated Distributor (I wish I had taken pictures, this thing is built better than the MSD I looked at), I've replace IAC, Checked TPS, new wires, plugs, cap/rotor, O2Sensor. My fuel pressure reads 45 psi at idle, and 55 psi with key on engine off. I checked compression across the board (fig'd I had a lifter not pumpin up) compression was like 150-155 on all cylinders. I have my timing set at 10* advanced with the ETC disconnected (for the cam). All of my plugs are white, meaning the ceramic part, but not LEAN white, more like perfect AF ratio. A balance test reveals NOTHING, no change in idle quality despite which plugwire is disconnected. I have NO vaccumn leaks, I regasketed EVERYTHING in an attempt to locate a leak, there were none (there are none). I have no check engine light, snapon scanner reveals no codes. I tried it with 2 different ECMs, same idle quality. Anybody have ANY ideas what this could be??? I've talked to 2 of the guys I work with, and it's got us stumped.

 

what's the fuel pressure reading when it misses? Also, has the pcv been replaced?

 

I know I responded already to your last post about this, but I will just reitterate that I think you know my car as well is top notch and immaculately mechanically maintained sparing no expense on whatever may have any seen wear. This injection system is just inherent to idle stumble with the crappy fuel we now have. My motor is brand spanking new-Not rebuild (very low miles still with only about 30,000 on it, Yet it continueally does the same thing you describe. When on the throttle at all above about 1200 ropms for me, it purrs like a kitten and is so smooth its flawless, but sit at a light for more than 20 seconds and it bobbles. It never did this up until about 5 years back even with the older high milage engine in it- it always used to idle perfect then(I have owned this car for about 13 years now.

 

We actually get pretty good gas here in Houston (we have most of the Gulf COast refineries supplying us). I've tried a few different brands of fuel, they all reap the same results. Chevron or Shell/Texaco. I've also tried running different octanes, and different fuel additives. ANyhow, I don't think it's fuel quality related.

 

Are you by chance running multi tip plugs like splitfire or the bosch +4's?

 

No sir, AC delco R42TS, the same ones the 2.8 use (I've tried hotter and colder...I run the colder for the jiggle gas).

 

I am having the exact same problem with my '87 2.8. It is about to drive me insane.

 

I haven't checked my fuel pressure in some time, bit I thought it should be around 38psi... If I'm right maybe your regulator is bad, dumping too much fuel...

 

It's adjustable BBK unit. I'm running a bigger cam, I'm using the extra pressure to help compensate for it (although in theory, fuel pressure won't help enrichen the mixture...The computer should auto compensate for such things...)

 

I had the same problem

Replaced EVER sensor that's attached to the motor. Replaced wires, plugs, cap rotor, rebuilt distributor, all new plenum and lower intake gaskets. Had the injectors cleaned ultra-sonically. New vacuum lines, New EGR valve. New EGR solenoid and vacuum switch. New IAC, TPS,......ad nauseam.......

Turns out, and I found this out by accident, when I was cable tying my spark plug wires shortly after a cold start-up, I burned my hand on that correguated stainless cross-over pipe that goes from the EGR valve to the upper plenum. That part of the EGR system shouldn't have been hot at all especially right after a cold start-up. The EGR valve only opens during certain driving conditions Now bear in mind when this car started acting up from the beginning, the FIRST thing I did was replace the EGR valve. All the symptoms of a bad EGR valve were there, bad idle, rich exhaust, ect....Apparently[and I'm only assuming this] there is a leak or crack in that cast iron tower that the EGR valve sits on. I couldn't believe that two EGR valves in a row would be bad. What I didjust for the hell of it was unbolt the cross over pipe from the upper plenum and inserted a sheet metal blocking plate between the plenum and the cross over flange. This straightened the idle right out. I couldn't believe after all the expense and hair pulling a lousy piece of sheet metal cured my problem.
Some will say that the EGR will keep the engine from detonating, I,ve been running the car with the EGR blocked off for almost a year now and these is no sign of this. Also, I don't have a problem with the throttle body coking up and the IAC getting excessively cruddy anymore. Blocking that pipe off was well worth it.

 

That's prettty neat, but it's not my problem . That was one of the first things I checked (vac gauge test). I guess i could remove the tower and make sure that the pintle thingy isn't sticking open due to a bad mating surface, I know the vac bladder is good though. And my motor isn't running rich, it's actually more on the lean side than I'd like (according to my white plugs).

 

EGR is definately not my problem either. Mine was blocked off for the 4 months proir and I just installed a brand new EGR just before it was smogchecked in june. No change at all blocked or unblocked.

 

same problem i have


we need to find out whats causing it

 

A coalition of forces....hehehe. I had three diff mechanics look at it (not for money, other mechanics I work with). I fear I may forever have a miss at idle

 

lol, i thought it was just a bunch of parts i need to replace. but since so many of you guys have the exact same problem i don't know what to do

 

Well, don't go part swapping until after you determine the problem (I'm a frigging mechanic, I should heed my own words, lol) . I did make a NEW DISCOVERY tonight though. Well, seeing how the temperature FINALLY dipped into the nice FAll weather I'm so used to ( ), I went for a cruise figuring some nice dense air would give me a power advantage in any races I might encounter (TPI intake OWNS). ANyhow, I'm ut driving around for like an hour, and My car Idles PERFECTLY FINE......#@$%!. *sighs*....Anyhow, so this is the first time it managed to idle right in the last 3 months, so I'm inclined to believe the cold dense air has somthing to do with it. I ruled out the coil as the culprit (That's why I drove around so much after I noticed it was idling right). The coil was nice and toasty upon returning home, and sits atop my headers, so that's not it. My next guess revolves around the IAT.... This quirky little sensor that I've never seen code on our cars. BUT, if it wasn't working, the temp wouldn't have an effect on the idle quality. So guys, any hypothesis? Better yet, anyone know a way to make the sensor think its cold outside (so I can test the weak theory when it heats back up)? Darn 3rdgens....always keeping my brain boiling...

 

actually the iac, was what i thought to start replacing

 

Tried that already...want my old one, lol. (Actually I think I threw it away in anger...)Every sensor on that motor is all new and shiny, hehe. Time to build me a bitchin new intake mani to match the shiny new parts...

 

lol yeah, i'm thinking about just getting a 2.8 and rebuiling it, complete with every sensor and ****

 

Save your brain, go carbed . If it weren't for my nitrous setup, I'd have already switched to Carb. Stupid computers are worthless unless yuou're aiming for fuel economy.

 

actually thats what i want is fuel economy, i like to get the best bang for my buck, but i guess since i'm only getting 470 km to the tank carbed couldn't hurt

 

Hey guys, I finally figured out what was wrong with mine. Turned out it was a timing problem. The Chilton manual I used for reference had the wrong instructions for base timing procedure-. I reset it using the correct method, set it at 10*, and now it runs great-. I feel like I should just throw my Chilton and Haynes manuals in the trash; I could fix things faster without them.
FbodTrek, you mentioned that you had a different cam. 10* might not be the correct setting for it. Maybe you already tried this, but I would tweak the timing 2*, then drive it and see if it is better. You could keep tweaking it 1* or 2* at a time until it is fixed, or until it is determined to be some other problem. It seems likely that you have a timing problem, because your description sounds exactly like the symptoms I had.

 

Yup I been there. No help. It's good to hear you figured your prob out though. One down, two to go, eh Kretos?

 

I drove mine last night and its getting fairly cooler here in So.Cal now at nights- low 60's high 50's lately. I noticed imediately it idling perfectly in the cooler weather and the winter gas. A few weeks back it was stumbling. It is definately heat and gas related for me.

 

I wish I could say the same. A few nights back I was thinking the same....but alas, no dice. SO, I still need to get it to my racecar guy. I'm tired of screwing with it, it's giving me an ulcer the size of Utah... My Birthday was thursday, I was hoping the good lord would be kind enough to give my car a miracle healing as a gift To top it off, I finally got to spray on someone in a race tonight....I lost, to a Volvo Wagon running 15 psi of boost and some other goodies So, here's my wish list:
POSI!!!!!
More juice (I have jets for 80hp)
A turbo that will teleport itself onto my engine
Finish my head porting project and get them installed.
Drop this crappy injection setup and throw a carb on if I can't figure out my idle prob.

 

My 85 had the same stumble.... I had 4 clogged injectors