Loopy idle

[96-2D-Hoe]

Forget AZ. $37 + shipping at RA for a Delco Coil for your 92 C1500 suburban

https://www.rockauto.com/en/moreinfo.php?pk=335800&cc=1301858&jsn=572&_nck=ZExt1ysfqhqWnq+EvUNdS3Txyey60IDtnjPWF5UU9J0BWQv7pvqZbkEUk86+AYIh3BPX4eQfsOg2pvrTzXeZctmUkmtrXupFzkEVrxo2PmuIvhSNzAgEt+153GQmy5/kAYpLxznz82SNhzlcB4mgQ5qiBhjxnBHU+LlmIYK9NXBAICWmk/P/zeZQrC9QkQa4CE7p5/ODt5YZdE2CPmw2Ruw3dVhll0iAeyVoaChhZR+7maO9d7ITfBqZRW65BxSJ9D3HZxnBVRmK+dwGTx3yBEPbTLlVp2zI4sRGub//itMSvCucaer3qkwK6VGuRDy0RQH7CgvMS/pxrxIr9S7kXotMBY436pVs

 

[PlayingWithTBI]

So - I should get a good quality coil and see if it runs OK?

I don't know of any parts houses that test ICMs

What brand ICM do you have? Did you use plenty of thermal paste under it? If it were me, I'd change the coil and then take it out for a ride and data log looking for unexplained jumps in timing. I caught mine (an almost new Pertronix Flame Thrower coil and Spectra Premium ICM) jumping while cruising at ~2200 RPM. The ICM will send a false pulse to the ECM which will think it's running faster and throw different fuel/timing at it, and your truck will surge or pop. In my case it jumped to 4775 RPM.

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Or you can just change it out with a good quality ICM...

 

[Texvet]

I will get a get a quality coil as you suggested. The ICM just installed is a Duralast DR140 from AutoZone. I put the quarter size dollop heat sink grease that was in the box with the ICM. I don't have a scanner, so I will install a coil and see how it runs.

I think I've seen the light regarding cheap parts.

Thanks again for your advise.

 

[Tim W]

I hope that fixes it. Report back once the Ac d part comes. Iv learned the hard way about cheap parts. I got an Az blower motor resistor and dang near caught my truck on fire.

 

[PlayingWithTBI]

I hope that fixes it. Report back once the Ac d part comes

^^X2. It may not totally fix your issue but, at least it's a start. Good luck.

 

[Texvet]

Update: It is with all due caution that I say.... The cold start after installing an Delco coil was positive. No bouncing tach. Idle stay rock solid when put in gear. I headed out to run some errands and see what happens. Will report.

 

[PlayingWithTBI]

So far so good, keep your fingers crossed.

 

[Texvet]

So far so good, keep your fingers crossed.

I had a little roughness at idle until it hit operating temp. Not nearly as bad as before the new coil. Every once in a while it would stumble, in gear at a stop light. Anything above idle speed was fine.

Does it sound like the ICM is suspect? Either junk to begin with, or damaged by the bad coil?

Do you know what the difference between Delco ICM part numbers 1943A and 1984A? The obvious difference (to me) is the 1984A cost $33 more.

 

[PlayingWithTBI]

Does it sound like the ICM is suspect? Either junk to begin with, or damaged by the bad coil?

It could be, no guarantee. YMMV

I think the D1984A is the current replacement or it might be their "Professional" line. When I bought the 1984A last year from Summit Racing it was $65.99, I see it's now $77.99

https://www.summitracing.com/parts/ado-d1984a/year/1988/make/chevrolet/model/c1500

 

[PlayingWithTBI]

Hey @Texvet any update?