87 TBI 350 intermittent timing loss

[Sam71395]

Hi everyone, my 87 kind of has me stumped right now. For the last few times Ive been using it, it will be sitting idling fine and then for a spit second the rpm drops to nearly stalling but then it corrects itself just in time before quitting. So Ive been doing some troubleshooting and hooked up a timing light to it, and what is happening is that at idle my truck will be at about 14 btdc and then randomly drop to 0 and shoots back up again, creating a big surge in the idle speed. It does this completely randomly, I cant find any rhyme or reason to it. I unplugged both the knock sensor and esc box (the one by the map sensor) and it didn't change anything, it still did it with those unplugged. I've looked for loose or faulty wiring and found none. the only time i could get it to stop is when I unplugged the temperature sensor, i didn't think that temp sensors affected timing on these unless someone else knows otherwise. some advice would be greatly appreciated.
also, has no issues starting, or running otherwise, and no engine light is on

 

[gmbellew]

I’d guess that you have some stray voltage zapping the ignition control module wires. Do you have a code 42?

 

[Sam71395]

i just checked, it showed code 43, it never lit up on the dash, can codes show up and not light up on the dash?

 

[gmbellew]

i just checked, it showed code 43, it never lit up on the dash, can codes show up and not light up on the dash?

sometimes. code 43 is the ESC. there is a diagnostic for it in the drivability manual

 

[Sam71395]

i just did the procedure for diagnosis on a code 43, and it seems to be pointing to a esc module, the knock sensor checked out the wiring has no visible breaks or is loose, so Im going to get a new module and let you know how it goes

 

[Sam71395]

just did the esc module, and drove it about 100 miles round trip today, it seems to have fixed my problem, thank you for the help