Whitey16 - did your alternator make a whistling noise that you could modulate with the gas pedal and if you did hear that whistle, was it consistent with the power loss? I hear a whistle around the time I experience these problems. I did replace the coil and tested a known good ICM but still have the problem.

 

No, I can't say I remember a whistling noise. Just the loss of power and the tach would also bounce.

 

Took it out tonight for the third test drive since remounting the ICM this morning. No stumbles or misses, excellent acceleration and averaging 20.8mpg. However...now the idle is high around 1100rpm. The connector for the idle control valve is missing the latching mechanism that secures it to the sensor housing and the insulators that go around the spades that plug into the sensor are missing or jammed into the sensor.

 

i have the same, i think, problem just started....

at 1800 rpm sometimes when i hover at the lowish rpm it will stumble and catch and last night when i was cruising in 6th for 10 miles and went to accelerate, no power, and the mpg actual showed 8 mpg on a cruise, like it was starving for air or something

 

Sounds like I have a similar problem as well. Car seems to run fine driving to work until I get to about a halfway point. The car feels like its loosing power no matter how much I press the pedal down, sometimes it even quits driving at 60mph, throw into neutral and starts back like like nothing happen and I can continue driving. I will try and pull the ICM and plug back in and see if that helps.

 

I wanted to post what I did as it has seemed to have fixed it so far (knock on wood).

I replaced the oil pressure sensor. I know there are some on this board that say it is not tied to cutting the fuel pump when pressure falls below a certain psi, but I was having an issue with it anyway. When I would be driving the down the road at a consistent RPM the oil pressure would fluctuate say 51-47-50-45-49 etc. It now stays at the same figure when the RPM is consistent.

I also cleaned the following connectors with electrical contact cleaner and plugged & unplugged them several times.
- MAF
- TPS
- Coil to cap (3 of them)
- Distributor to ECM

I don't know which one for sure fixed it, but I have driven it about 15 times now and it has been fine.

 

same thing was happening to mine changed the coil and ingnition mod. and runs fine now, probably didnt need the coil but what the heck, I was in there.

 

Turns out my problem was with the ECM, the fuel injector signal was dropping out. I threw a few parts at it before taking it in and paying a mechanic to hook up a laptop and burn some gas driving around to finally figure it out. On the bright side I have a new fuel pump, opti harness, Plug Wires, various harness connectors, coil, MAP sensor, fuel filter on top of the optifart, water pump, hiflow cats, shocks, tires that I actually did need, it's been an expensive summer :-)

 

It didn't fix it after all, it came back this morning on the way to work. It actually lasted the longest it has so far, probably 3-4 seconds. The accelerator had no affect at all, nothing else seemed to drop out or act weird while it had no power, it dropped down to 500-600 rpm, lights seemed fine, and then it came back and worked OK. I checked again and it did not set any codes.

I do have a new coil & module I could install, but I am getting ready to put it away for the Winter so I may not know if it is OK until next Spring.

 

If it was ignition it would die. You need a way to monitor fuel pressure while you are driving it.

 

on the obd1 cars the tach gets its signal from the coil. in my 91 camaro my coil was ****ting the bed and the tach would not work correctly at the same time the coil was dying. replaced coil and all was well.

 

About all that's left is the ECM. You say no codes were set - but will it flash "12"? If not, get a used or rebuilt one. My wife's 91 L98 did similar things but would set 3 unrelated codes - replaced and all OK.

 

It does flash "12" no problem.

I thought it might be the fuel pump also, but wouldn't it set a code for lean condition at the oxygen sensor? Since it doesn't set any codes, it seems like it must be something not connected to a sensor. It never runs rough or anything, it just gone and then back in the space of a couple seconds.

I think I am going to bite the bullet and call Gordon Killebrew this morning and see what he has to say. Pains me to have to pay for advice, but I don't want to throw parts at it either.

 

I talked to Gordon today and he thinks I need to do the Minimum Air Set Procedure, which he described as:
First ohm the injectors to make sure none are shorted
Take boot off throttle body; clean the TB & the plates inside using TB cleaner
Jump the ALDL connector under the dash A to B
Turn key on (but do not start) for 30 seconds, fans will run which is normal
Unplug the IAC 4 square connector (pintle will move out to seal it off)
Remove the ALDL jumper
Disconnect the 5 volt bypass wire by the wiper motor (Tan/Black Stripe, single black connector taped to harness)
Start engine, probably won’t idle
On left side of throttle body is a little aluminum plug, use a nail or screwdriver to pry it out
Use a 15 thorax tip to adjust to 450-500 rpms, might need to go higher and back it down (base idle)
Check base timing, should be 6 degrees
Shut off the engine
Plug IAC & 5 volt bypass wire back in
Disconnect the battery to clear the code 42 that was set
Using a digital volt meter adjust the TPS to .54 to .56 volts
Measure across A-B on TPS switch, Black (ground) – Blue (monitor)
Loosen screws, moving up ups voltage, moving down drops it
Start it up and warm it up
Idle will come up. In gear it will drop a bit and then come back up.

He said this should be done every tune up. At least I don't have to buy anything to try this, but not sure when I will get the time to drive it afterwards since they are saying snow/rain mix next week and colder after that. Might not drive it again until next Spring.

 

It didn't fix it so I called Gordon back and learned some new things to try. Supposed to rain & snow starting Wednesday so I probably will not get to this for a while, but this sounds promising.

[1] Fuel Pressure issue
- 89’s had a problem with the fuel meter contacts burning
- Remove the pump/sender assembly and unplug the Black 3-wire connector (Pump, Ground, Level)
- Connectors may be black & burnt.
- Unplug them and scrape clean, use contact cleaner
- Use a safety pin to tighten the connectors if possible

[2] Convertibles have an issue
- Under the carpet near the right rear hinge is a pocket where the connector is from the rear body harness
- Raise the decklid and pull back the carpet
- Terminals could be green & have corrosion (or even gone)
- Scrape & clean with contact cleaner

[3] Condensor in the distributor could be loose

 

hey i bet the egr valve is opening prematurely due to malf w egr solenoid providing too much vaccum and makes car fall on face happens alot on all kinds..try disconnecting or plug lines to elim. operation

 

i may be of help,,many yrs. 22 master tech..lots of time on the tpi L-98s...

 

If it was the EGR, would it be a constant thing? It went for weeks and didn't do it, then it came back and was fine for a week and did it again; it is very intermittent. It has never run rough or anything; it's there, gone and back again in 1-3 seconds. The EGR was new 3 years ago, but only has 1000 miles on it.

 

If the fuel pressure checked out and the spark is good - myself - I'd change out those non ethenol compliant fuel injectors at this point (I recommend you get with Jon @ FIC Injectors he'll size you up). Long story short - I had a set of the stock Multec injectors causing issues but they all tested OK when the resistances were checked no matter how to tested them. You really need an oscilloscope hooked up to see an intermittent problem in action. I changed my injectors out and all was well again with my '89.

Final thought from me is to give some of the MAF circuit components a "tap" test:
Start the car and let it get to up normal operating temp where the problem normally occurs. Pop the hood and tap (with a screwdriver handle) on the MAF sensor and/or MAF power relay while the engine is idling and see if the problem reoccurs.

Good luck - make sure you post back what fixed the issue.

 

the egr malf can be intermittent,,especially if its what controls the operation..the solenoid only lets vac to egr at certain times..solenoids stick open themselves and or ecm grounding the solenoid when its not supposed to....you really need to plug the vac line to egr and road test for process of elim...also need more details on ur driveability symptoms ..if you called me we could narrow this down easier..704-492-8355-----kelly..