I just picked up an '88 L4 standard trans coupe 3 mths ago, and as I was driving down the road the car begins flashing SES light crazy before it stalls out. I try to restart it and no go. After grounding out terminals into test mode, it flashes codes 14-34-35-55. I replace all the coolant sensors and map and vac line, & it runs and I drive home.
On the way it stalls again & flashes same codes! Funny thing was..
I DID NOT HAVE PINS GROUNDED!!
I turned off key and sat for a minute, turned key and SES acts normal, car starts up and start home.
Stalls two more times, I flick key off for 15 secs while in gear, back on and runs fine each time.

Any ideas? I've cleaned grounds and checked ECM connectors and reseated them.

Who has run into the ECM going into diagnostic mode by itself?

Thanks, and sorry for long post. Tried to provide as much info I could.

[This message has been edited by Fishogs 84 (edited 06-20-2014).]

Bad ECM?

Will a bad ECM keep the car running?
I've read 15 pages of posts using search topic "ecm" and can't find a problem like this.

At a loss here. HELP

Yes. Even modern cars. My Hummer had a bad ecm and it would run at times.. Also, I had a similar issue to what you are describing in an s-10 and after a LOT of prats swapping, that was the culprit.

Disconnect the ECM at it's main connector.

Then with an ohm tester, check the ALDL connector for any shorts. Looks like the test pin of the ECM is getting grounded (and maybe other pins as well)

My thanks to you both!
I think I found another ECM to try, & definitely going to ohm out aldl before installing.
Looks like the po installed an 86/87 motor as it does not have DIS.
Been a very interesting project!