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I've been driving my car all week since I fixed (batee) my digital dash and have been noticing a slight stumble sometimes idling and decelerating. Yesterday while at a drive through it happened again when I was at the window and stalled with the Service Engine Soon (SES) light on. I started it immediately and it ran for another minute and stalled. So I left it off until I finished my business and when I started it, it stalled again … and when I restarted it and it jumped to life with a loud pop out the exhaust but it stayed running until I got home.

Checked codes … normal 6-12s

So I started it and left it idling in the driveway for about 10 minutes and it stumbled and stalled again. Immediately checked codes and this time the SES light stayed on! No 12s. I turned the key off and removed the jumper and restarted OK. Let it idle another 20 minutes before it stumbled and stalled again and this time the codes were normal, 6-12s.

Last night I changed out my computer (ECM) with a spare unit on the hope that it would fix the issue. It ran in the driveway for 1/2 hour so I test drove it and it stalled again. Finally got it running again and drove it home.

Today it ran fine in the driveway for 2 solid hours no stumble or stall. Monitored fuel pressure @ 42psi no drops during the whole time. What possibly could be causing this?

After driving it for a day with no issues this morning it stalled and now will not start. Normal codes (6 - 12s) Fuel pressure is 42PSI and would NOT start with starting fluid so that eliminates the fuel injectors as being a problem and I have a no-spark condition!

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  • I don't remember ... is the 86 carb'd or throttle body fuel injected? Does it have an HEI distributor?
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 12, 2019 at 23:29
  • HEI - 8 fuel injectors tuned port induction
    – 3dalliance
    Jan 13, 2019 at 0:07
  • Ah, should have remembered (same setup as my 86 IROC-Z). When the engine stalls and you restart it, does it start right back up every time? Something you can try is cleaning your Intake Air Control (IAC) valve. It is right at the bottom front of the throttle body. When you do that, ensure the intake is off and spray the entire area down with carb cleaner. Also, be very careful with the IAC, as the pintle on it is delicate. If you push or pull manually on it, you'll strip the gears.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 13, 2019 at 0:13
  • By "intake" I mean the intake tubing forward of the throttle body, not the entire intake (aluminum part attached to the engine)! Sorry, hope that wasn't confusing.
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Jan 13, 2019 at 0:22
  • I've heard of the IAC but never have fooled with it. I'll look it up in the FSM and check it out - thanks @Paulster2
    – 3dalliance
    Jan 13, 2019 at 16:04

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Thanks to Paulster2 for suggesting to check the IAC. This is what it looked like when it came out:IAC

IAC

I think it is extremely carbonized. I didn't bother cleaning it, just replaced it and it started and idled and drove it for a test and all seemed fine. I'm still not convinced it's fixed though.

Two days later the problem resurfaced and will not start now. Fuel pressure is 42PSI and would NOT start with starting fluid so that eliminates the fuel injectors as being a problem and I have a no-spark condition!

All morning working on it I narrowed it down to the ignition coil. When I pulled it it smelled burnt and the connections were all open circuits. Replaced with a new one and it fired right up first crank.

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