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Discussion Starter · #1 ·
I replaced the Idle Air Control (IAC) valve with the GM aftermarket equivelent.

I started the truck after the part was installed and it ran fine, better in fact.

I went to drive the truck this morning and it would barely idle. When attempting to throttle up its very rough and doesnt rev smoothly. Once the motor warmed up it was able to idle without any interaction from me but was very rough. Also, there is a noticeable hesitation when depressing the throttle.

I didnt touch anything else on the motor.

Im thinking it could be the mass air flow sensor. Does anyone else have an idea?

Thank you
 

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Try setting the base idle. This made a huge difference for me. Also, run some carb cleaner through the IACV circuit to make sure it's clean in there.

I've read that it sometimes takes the ECM a while to "learn" a new IACV. Not sure if that is the case but after replacing mine 3 times I finally checked the base idle and it was way off. After adjusting that and cleaning the plenum and idle passage mine has been running great and idling solidly.
 

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Discussion Starter · #3 ·
This is very helpful.

I had a Classic a few years ago and had to replace the IAC. I vaguely remember having to "program" the ECU and calibrate the new IAC valve. The truck ran great after and I never had to adjust the base idle.

Do you ever recall having to do that?
 

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Don't fool around with the base idle until you have exhausted all other possible causes. It's sealed for good reason.
 

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Discussion Starter · #6 ·
Last night I replaced cap and rotor with no change. Next, I cleaned the mass air flow sensor with CRC MAF cleaner and scrubbed the throttle body clean. There was no change in idle speed or quality. The flame trap was the next item on the list, once removed it looked like it had never been cleaned. I have never seen one of these things so packed with carbon and oily sludge. Cleaning that out as well as the connection tubing made a difference. Idle quality improved slightly.

I then went through the procedure for setting base idle. Before adjusting it was at 775-800rpm. After following the procedure found online the idle speed is better, 725-750rpm, but the idle quality is only okay. If the motor is revved it settles down quickly and is smooth but if you let sit for thirty seconds the motor stumbles slightly. I may be nit-picking but its run dead smooth for the past two years.

I am now looking at plugs and wires to see if idle quality can be improved. Ordering OEM replacement components, no cheap stuff here.

Does anyone have info on ignition amplifier modules? If plugs and wires dont work Ill be looking at the amplifier and coil.

Thanks for all the feedback!
 

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Discussion Starter · #7 ·
Tried to start thr truck this morning and had the same issue as befor, low idle.

I put the old IAC valve back in and it runs perfect now. I may have got a faulty replacement part.

I am still going to replace plugs and wires since its been two years and should be showing some wear.

I will report findings as components are replaced.
 
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