Intermittent Stall and Rough Restart

[Jfrost]

Trying to fix a few lingering issues on the Fiero before next weekends Indian Uprising car show. I have an idea of what to test but wanted some additional input before digging in.

Car is L67 swapped with a Northstar TB, LQ4 MAF (recently replaced) and GenV supercharger. The engine will randomly stall when idling at red lights, stop signs, or in the garage, never when actually driving. When it stalls I have to give it gas to keep the engine running otherwise it will die right away. When it does stay on, it runs real rough and misfires for a bit before returning to normal. Other times I loose all electric power. The latter is likely caused by my battery being on its last limb due to how infrequently I drive the car, so that will get tested and fixed, my main concern is when it stalls and runs rough on restart. Also of note, sometimes at startup the RPM’s will surge before setting into an idle.

First thought is either an ICM, cam sensor or IAC valve. The ICM and coil packs are tucked under the rear cowl with not much air movement which could have caused their demise.

Any help would be appreciated!

Click to read more...

 

[GTPpower]

Any codes?

 

[Flyn]

^^ This. And, fuel, air, spark.

As a case in point, I bought a lawn mower that was revving/dying every couple seconds for $10. Put a new air filter on it and the revs smoothed out immediately. It was starving for air. Figure out which one of the three it is.

 

[Jfrost]

Any codes?

No related codes, only items DTC’s for auto trans that I’ve yet to delete.

^^ This. And, fuel, air, spark.

As a case in point, I bought a lawn mower that was revving/dying every couple seconds for $10. Put a new air filter on it and the revs smoothed out immediately. It was starving for air. Figure out which one of the three it is.

Turns out it was a jumper wire taking battery voltage from the positive cable on the starter to the junction block distributing battery power to the car. As I dug further into wiring diagrams after my battery tested good, I remembered seeing that wire look a little worse for wear last time I was under the car. When I went to start the car for the first time years ago I had no power at key on/engine off and quickly realized I forgot to tie battery voltage to the main junction box and threw something together real quick as a temp fix. That temp fix was 10 gauge wire rated for home use and terminal ends I had to open up to fit over the starter solenoid long. When I inspected it the end by the starter had some corrosion and the wire was loose and able to be pulled out with not that much effort. I’m surprised this didn’t cause problems any sooner. My guess is this wire/connector was not fully transferring voltage from the alternator back to the battery to properly charge it. Add that to how infrequent I drive the car and it leads to low operating voltage, especially at idle, where the IAC valve can’t properly operate and stall the car.

I went to autozone, got an 8 gauge battery wire and terminals and made a new jumper wire. Cars been running a lot better since (knock on wood). Sometimes the problem is simpler than you make it out to be.