Surging idle on cold start

K-Man said:

Is there a proper way to calibrate the IAC when installing new?

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No, you do need to calibrate your TPS though. With KOEO it should read ~.4 - .5VDC and at WOT ~4.8VDC or somewhere around there.

The IAC is a stepper motor which the ECM commands to open and close. When you turn off the ignition it'll open to its "Park Position" (mine's at 143 Steps). Then when you start the engine it'll close to a position determined by other inputs like CTS, RPM, A/C on, etc. That's why it'll rev up pretty high at first, then idle down. When warm, at idle, it should be ~10 steps. If it's at zero, you probably have a vacuum leak. If it's higher, your throttle blade stop may be set too far open.

K-Man said:

I remember seeing a video about removing battery terminals and shorting hot and ground wires for a few minutes to drain any capacitance in the ECM which resets all parameters?

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That will reset volatile memory, in the hardware, like your BLMs etc. It won't reset any of the .bin files.

PlayingWithTBI said:

When you changed it did you use the same chip from your old one? Maybe your "Choke" tables are different?

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used the old one, the AC delco re-mans don’t come with the prom.

Sabinoerc said:

You might try to narrow down if your problem is just during open loop or also during closed loop. memory is you can short pins on the ALDL connector to show if it’s in closed loop.

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Do the same thing you'd do to view "codes" with a paper-clip or jumper wire on the ALDL (NOT the OBD-2 style.) KOEO, you get blinky codes.

With the engine running, you don't get codes. You get open loop/closed loop, and rich/lean. And you'd better watch carefully, 'cause its a pain in the axx.

Check the speed of the flashes. The speed tells you whether you're in open or closed loop.

Check the amount of time the light is "on" compared to "off" That tells you rich/lean.

I haven't actually done this in thirty-plus years. I don't remember if fast flashes means open or closed loop; and I don't remember if the light being "on" more than it's "off" means rich or lean.

That's in the service manual, though.

Hint: Use a scan tool instead.

PlayingWithTBI said:

The ICM gets hot (maybe not properly installed with thermal paste),

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Do people actually install modules without the heat-transfer compound? I've never seen it done. I thought everyone knew about that.

I have seen recommendations on this site to use "lots". That's not really good advice. A heavy coating mostly just squeezes-out when the screws are tightened.

PlayingWithTBI said:

I sprayed some water on the coil and it almost died. You can see the arc burning between the body and the iron.

Replaced the coil and all is good. YMMV

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Dang good work! I've got no use for cheap--but expensive--imported ignition coils.

K-Man said:

Is there a proper way to calibrate the IAC when installing new?

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I gotta think on this. Seems to me there's a process of turning the key, unplugging the IAC connector, turning off the key, reconnecting...but I don't remember the steps, and I'm too lazy to look it up right now. And maybe that doesn't apply to "new" IAC motors.

K-Man said:

I remember seeing a video about removing battery terminals and shorting hot and ground wires for a few minutes to drain any capacitance in the ECM which resets all parameters? Does that sound right?

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Do you really need to short + to - for "a few minutes"?

I thought all you had to do was disconnect one cable for fifteen seconds.

Schurkey said:

Seems to me there's a process of turning the key, unplugging the IAC connector, turning off the key, reconnecting...but I don't remember the steps, and I'm too lazy to look it up right now.

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That process is for setting your "Base Idle", to ~100 RPM below target idle, with the throttle blade stop. Then you can fine tune your IAC steps feedback while maintaining target idle with engine at operating temps.

Schurkey said:

I thought all you had to do was disconnect one cable for fifteen seconds.

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Yeah, or disconnect the negative cable and touch it to the positive one. You don't need to disconnect both.

Schurkey said:

Rainy, 45 degrees, runs shiitty, maybe stalls?

Does the flapper on the air cleaner snorkel actually work? Draws heated air from the heat stove around the passenger exhaust manifold, through the expando-tube, into the air cleaner?

'Cause this sounds a lot like throttle blade icing to me.

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It doesnt have a flapper valve and there is no sign that it ever did.
Carb icing was my first thought too.
The "dryer vent" heat tube is brand new.
But, I also have bad valve stem seals that I havent dealt with yet.
Below a certain temp. It starts pig fat rich and surges but it clears up after a bit.
I suspect an open loop/ closed loop problem.
But isnt that a bit quick to go to closed loop?
Do you get to that when its below a certain temp?
It happens at about 45 degrees or so.
I know I should get live data.
I know that.
But this is really common problem.
I suspect that this presents as a universal problem
But the souce of the problem may differ for each of us.
In other words, The end result is not the cause.
I dont know
Im just gonna drive it untill it falls apart and drops me on the road.
Then I will get another one.

thinger2 said:

It doesnt have a flapper valve and there is no sign that it ever did.
Carb icing was my first thought too.
The "dryer vent" heat tube is brand new.

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Have you looked inside the snorkel? These trucks don't have a vacuum-powered flapper with a vacuum can on top of the housing. It's all internal.

I don't know how it can have a "dryer vent" heat tube, but not have a valve that controls the heated/ambient air flow so as to regulate temperature.

Mine is 100% stock, so I’ll report back if it’s operating correctly. My 1st thought was that.

Schurkey said:

Have you looked inside the snorkel? These trucks don't have a vacuum-powered flapper with a vacuum can on top of the housing. It's all internal.

I don't know how it can have a "dryer vent" heat tube, but not have a valve that controls the heated/ambient air flow so as to regulate temperature.

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Ive had it off a hundred times.
Its a 94 k500.
Has the plastic tube from the air cleaner to the intake.
But. I will look again.
94 is an odd year
Very transitional
A 94 does not have a flapper valve.
It has a cold air intake with a heater tube off of number three.
And thats all it has.
Pretty chumpy right?
94 is the first year for a lot of strange things.
First year of R134a
First year of all of the things that make a 95 a disaster to own.
The last year of silicon seals that you cant add synthettic to.
The G80 diff with the silicon seals.
And on and on.
Owning a 94 gmt400 is all about telling yourself how friggen smart you are cuz you didnt buy a 95 gmt400

95 a disaster?, I had a good friend mechanic, who worked for GM, who back in day the said, ”stay away from the 96+Vortec” because they had so many issues with those, haha. I got my 95 in 97.

Now the concensus is stay away from the new stuff.....sounds familiar.

i guess 20+ years later is an easy call.

1997 said:

95 a disaster?, I had a good friend mechanic, who worked for GM, who back in day the said, ”stay away from the 96+Vortec” because they had so many issues with those, haha. I got my 95 in 97.

Now the concensus is stay away from the new stuff.....sounds familiar.

i guess 20+ years later is an easy call.

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The first year on any obd2 is a mess.
The last year of any obd1 is a mess.
Those transitional systems are manufacturers using their customers for quality control.
Which is normal.
Any major system change or engine or drivetrain change should be avoided.
Let someone else hamster that.
For proof, I present you with the first gen Nissan cvt transmission.
Or perhaps the 2005 Honda.
Or maybe the Caddilac 2 4 6
Dont buy the first gen of anything.
Let somebody else camp out at the dealership.