i got off the highway and came to a stop light. i went to take off and the car didnt want to leave idle speed. it bogged and backfired and stumbled. as soon as i pushed the clutch back in, it idled fine. then it took right off, no problem. i came to the next light and the same problem. it is fine at idle and cruising speed. it doesnt do it all the time, just random times. i also noticed it a couple times when i hit the gas on the road, it didnt want to take off at all. any ideas?

 

Doc,

You still fighting that IAC/hesitation/TPS problem? Get us up to speed on what you have done to the fuel and control system recently.

 

ive replaced the IAC, the injectors are leaking i know that, im pretty sure i have a MAF problem (i unplugged it and it got better), but this is something completely new that just appeared a few hours ago. the ignition system is at most, 9 months old. except for the coil. im thinking coil, TPS. i thought the MAF, but i unplugged it and it goes to a default setting. it still did the same thing, so that excludes that.

 

I have failed to see anything regarding a "Check Engine" light or any error codes. Are you getting any errors?

Lacking the nasty yellow light and resultant error codes, I'd strongly suspect a vacuum problem. Likely candidates for your symptoms would be the EGR (sticking or not sealing well after opening) and the brake power booster leaking internally after a brake actuation.

One means to eliminate the EGR is to simply disconnect the vacuum line so it cannot operate. You'll get an error code after driving it at normal cruise for some time, but at least you'll know why the code is there.

As for the brake booster, you can disconnect it and drive the car with no power assist (no fun at all, and can be dangerous) or rig a string of vacuum hoses and adapters so that the vacuum source to the brake booster has to route through a relatively small oriface to rebuild vacuum in the reservoir. This way, if the brake booster is failing, the symptoms will be more like a small vacuum leak as opposed to a large one. You'll also be able to tell by the power assist falling off after the first brake actuation rather than the three or more that the vacuum reservoir is supposed to provide.

 

i didnt get any codes. this morning i was checking it out and it got progressively worse until it wouldnt even run anymore. i replaced the coil and it idles now, but wont run for poo if you try to drive it. im not anywhere near the car for probably a week so i wont be able to do anything for a bit. i had it hooked up to the TECH 1 this morning, everything was reading normal, for the lil bit that it monitors. any other questions, let me know and i should be able to answer them.

 

oh, i forgot. when i was monitoring the injector pulse width, a few times, and just for split second, it would drop to 0 and then back to normal. i know the injectors are leaking, but it shouldnt cause the problems im having. just thought that may help.

 

Doc,

It seems like some of your data fits into my theory. Here's my train of though on your symptoms. Remember that sometimes the engine isn't at the front of my trains, so please bear with me.

Your '88 2.8 uses a Delco digital (FM) MAF instead of an analog MAF like the TPI engines, and your engine has no MAP sensor. Scanning the inputs with a TECH I would not necessarily detect anything out of range, since the ECM on your car has no way to monitor MAP/vacuum.

Your problem occurred after some highway driving, during which time the EGR should have been active and opening. At part-throttle cruise, you will not notice anything abnormal if the EGR is opened. Once you hit the exit ramp and were at idle, the EGR would be getting no vacuum supply from the timed port on the throttle body, so the EGR would not open. As soon as you tried to accelerate from a light, the vacuum port on the TB would supply vacuum to the EGR, and it would try to open, stalling the engine. If the EGR valve or solenoid were sticking, they could cause those symptoms.

A similar thing could be happening with the power brake booster, with the vacuum valving intermittently sticking open.

Since you're not running well at all now, just remove and plug the vacuum lines to the booster and EGR to see if that helps.

As I recall from your last episode with the car, you had replaced everything including the HEI module, and it made no difference. Now you have replaced the coil, and there is only a minimal difference at best - and possibly only because the engine was allowed to cool a bit while you made the switch. I'm leaning away from the ignition theory and toward the mixture theory on this one. Diagnosis isn't easy with some of these odd problems when we can't see/hear the car, but we'll get there.