Howdy everyone.
I've got a 1991 Trans Am with a 5 speed, 305TPI that has SLP runners and an adjustable FPR. The PO had this setup and I haven't done anything to it since my purchase. The fuel pump and injectors are a year old. As well as the coil and wires. Plugs read clean.
The engine runs very well with the exception that occasionally at cruise- and only with load- will it completely cut out then fire back up.
The worst instance of this happened today while cruising at 70mph at 2400rpm-ish. The engine cut out then fired right back up without me needing to use the key.
This is first time I've happened to be looking down and observe what happened. I was able to watch the tach swing from 2400rpm to about 800rpm, then swing right back up.
Occasionally the engine stumbles around 1k rpm at 40mph as well but acts right fairly quickly after.

Sometimes while driving, the OBD displays as Code 32 for the EGR system. It used to display a code each time I drove the car, but I replaced the EGR valve and the intake air temp sensor since they were both original and I was under the plenum anyway. The code sometimes come back, but doesn't always effect the drivability.
That said- occasionally the light precedes the stumble. In todays case on the highway, it did not come on until after.

The engine idles beautifully and can rev through the rpm band when in neutral whether the SES light is on or if the engine is hot or cold.

I tried searching for vacuum leaks with starting fluid when the engine is cold and hot and haven't found anything.

Its starting to drive me nuts. Do you guys have any other suggestions? I plan on replacing the plugs this weekend, but don't have a lot of faith that this will fix it.

 

It could be a ignition related issue like icm or even injectors. Are they the stock multecs grey body injectors?
you could ohm them while engine is warm.

 

They're gray body, yellow top injectors. I failed to mention that they're only a year old as well.

 

X2 on the ICM. Also make sure your battery is bolted down. If not it can tilt backwards and the positive and negative will hit the body and cause the cutting out as well. Been there done that.

 

X3 on ICM. Sounds like the exact symptoms mine had when the ICM was malfunctioning. It will get worse. Make sure if you replace it to use thermal paste (usually supplied with new ICM) on the back where it contacts the distributor. I would recommend you purchase an AC Delco ICM. The parts store versions have a pretty spotty reputation.

 

I think you guys are right. Once upon a time I had an '88 with a similar problem and forgot all about it.
A new AC Delco ICM is on order with fingers crossed!
Thanks for the help! I'll post back with the results.

 

UPDATE
Yes, the Ignition Control Module was indeed bad. Most of the grease was missing so I wonder if it could've been resused, but it didn't make sense not to replace since it was apart.
The car is amazing and now I'm not afraid to give it some gas to enjoy the torque without that feeling in my stomach that wonders if the engine will abruptly stop making power when I need it most.

Thanks for the help!!

 

Glad you found the issue

 

Second update!

Just kidding. The ICM did not fix the issue. Though it never hurts to have a new piece with new grease on it.

The problem ended up being a worn wiring harness at the back of the engine near the top of the transmission tunnel. The wires were frayed, insulation was rubbed off, and the wires were grounding out causing hesitation over bumps and uneven surfaces as well as occasionally when the engine was torqued.
Wanted to be sure others check this area should they have the same problem.

I still have that pesky code 32 though!

 

https://www.thirdgen.org/forums/tpi/...-solenoid.html

 

Whoa! Thats some amazing detail. Thank you very much. So far it doesn't affect anything (and I don't have emissions) but it'd be nice not to have the stupid light illuminate 25-30 minutes after turning on the engine.

 

So pull the cap, get a good look at the PU coil. Pull the connector, ohm between the two pins. Then move the little harness up and down while ohming it. SHould stay rock solid at IIRC 700 or 800 ohms and not flucuate.

Now, if after you pull the cap/rotor and see the PU coil is greenish color instead of nice wire wound copper, replace it.