Diagnosing Rough Idle Hell

[DylChrFla]

IDK what happened with my post, I saw 2 posts and changed one to double post, now the other one's gone.

Anyway, you're describing a fairly common issue with the ICM and/or coil, it runs fine until it warms up and starts stumbling. TunerPro won't tell you the ICM is bad but, you may trap a sudden spike in RPM during a data log.

The ICM will send a random pulse to the ECM which, in turn, thinks the engine is running faster so it'll change the SA and injector DC to coincide with your SA and VE tables for that speed.

That’s probably the only part of the ignition system I’m yet to touch. I’ll mess with it and hopefully that will solve my issue.

 

[red98]

That’s probably the only part of the ignition system I’m yet to touch. I’ll mess with it and hopefully that will solve my issue.

The ICM is also the biggest POS in the ignition system, its what I call a "glovebox part" meaning, keep a spare in your glovebox.

 

[Schurkey]

The ICM is also the biggest POS in the ignition system, its what I call a "glovebox part" meaning, keep a spare in your glovebox.

HEI modules of all configurations--4-, 5-, 7-, and 8-pin varieties--are THE most-reliable electronic ignition systems on the planet.

If you're repeatedly popping modules, you're either buying ****** Chinese knockoffs, or you've got a failed ignition coil drawing excessive current from the module.

For the record, defective coils are an epidemic problem with "new" coils made in China. I grab used OEM coils and HEI modules from the Treasure Yard whenever I can.

 

[PlayingWithTBI]

HEI modules of all configurations--4-, 5-, 7-, and 8-pin varieties--are THE most-reliable electronic ignition systems on the planet.

If you're repeatedly popping modules, you're either buying ****** Chinese knockoffs, or you've got a failed ignition coil drawing excessive current from the module.

It's a symbiotic relationship between all members of the ignition family, somewhat like a commune, if one teammate doesn't pull his/her weight, the others get burned and refuse to participate or contribute, JK!

The 2 biggest causes of electronic failures are heat and voltage spikes. Take care of these and you're good to go!

 

[alpinecrick]

The ICM is also the biggest POS in the ignition system, its what I call a "glovebox part" meaning, keep a spare in your glovebox.

I learned that with my 91 LD K2500.

I wish this forum had been around 20 years ago......

 

[96TahoeDoug]

It's a symbiotic relationship between all members of the ignition family, somewhat like a commune, if one teammate doesn't pull his/her weight, the others get burned and refuse to participate or contribute, JK!

The 2 biggest causes of electronic failures are heat and voltage spikes. Take care of these and you're good to go!

The forward biasing of a transistors P/N junction only has finite silicon to perform x amount of switching. It's chipping away at a ****. Shelf and operational life of consumer grade parts - oxygen itself corrodes internally. Can't last forever. Current flow is the monster. Agreeing from another angle

 

[DylChrFla]

The ICM is also the biggest POS in the ignition system, its what I call a "glovebox part" meaning, keep a spare in your glovebox.

Sorry for the late response, but I finally got around to changing out my ICM. The one that was installed seemed to be an original GM part. I bought an AC Delco unit because I read about trouble with other manufacturers. I did notice a slight change in idle quality but the exhaust popping behavior under no load still prevails.

 

[studigggs]

So I was just thinking about this today. About 15 years ago I had a rough idle, did my standard diagnosis of the time by hitting the forums and, rather than diagnose, I swaptroniked most my sensors with crap Autozone/Oreilys/no name sensors. Dummy me threw the OEM sensors away thinking "I had brand new ones...why would I need these old things?" Well, the idle issue turned out to be the fuel pump all along, but after the new pump was installed, the idle never was where I remembered. I had never really noticed idle driving this truck, but after my parts bukakke, it surged, was rough at times...it never stalled, just noticeable and 'off'. Over the last 4 years, I've corrected my error by replacing all the AutoZone sensors with AC Delco or GM Genuine (not Gold or Silver) sensors, and the idle is perfect. Ditching platinum plugs, no name cap, rotor and wires for Delco OEM items helped a bunch. So, just a thought and a warning not to ditch those OEM sensors. They may be made in the same factory in China or Mexico, but I would be willing to bet that GM/Delco lot tests or at least provides access to factory test fixtures to qualify a part as GM genuine, gold or silver.

 

[Schurkey]

parts bukakke

Thanks for that. Mind if I "borrow" that phrase?

 

[red98]

parts bukakke

Simultaneously the most glorious and disgusting phrase I've ever heard as a parts man.