Air Conditioning causing truck to stumble

[chevymotocross]

Since I've finished the suspension work on my truck, I've started driving it again. It's had these symptoms before as well. When I turn the a/c on, the truck stumbles, and occasionally stalls out at lights.

Fuel pressure seems fine at 13 psi. Truck does not do this when the a/c is off. System blows nice and cold.

Is there some type of switch that isn't working which bumps up the idle with the a/c?

305 TBI engine.

[chevymotocross]

I just did some searching and learned the IAC controls idle as well as when the A/C is turned on, it is suppose to tweak the idle. Also, I learned it always different cold idle settings which I forgot to mention, the truck runs like POO for a few minutes when started cold.

I'm going to try cleaning it with some TBI electrical safe cleaner.

[Chionos GMs]

Yeah my moms 92 Burban had the same problem and I replaced the IAC (Idle Air Control). I will get a pic of the location if you need?

[Chionos GMs]

I pulled this out of one of my threads

Originally Posted by ChevyTech

Being it ran faster after unplugging the TPS shows that the IAC must be working, at least somewhat. The question is how well does it work. It should be able to compensate for the A/C load and control the idle speed. It is normal for it to dip some but the IAC should bring it back up.

The IAC is a stepper motor and uses short pulses of electricity on the wires to move its position.

It takes good equipment and someone that is proficient using the equipment to test the IAC electrical pulses. For the novice I suggest using Noid lights to check these pulses. With no equipment the best you can do is to see how well it can change the idle speeds.

Unplugging the TPS with it running will cause it to run fast because it set a trouble code and is running in a backup mode.

Here is some IAC information:
IAC passages can get plugged up with carbon or muck. The IAC units get erratic as they get old and stick. Use care when cleaning the IAC. The IAC should not be cleaned with carburetor cleaner or other harsh chemicals. If the chemicals get down inside the IAC, it will damage it.

A bad TPS can make it so that the ECM does not know the correct throttle position and the ECM will not move the IAC.

Cleaning
To clean the IAC, you should remove it, and use a wet rag to wipe the tip of the plunger, while holding it with the plunger pointing DOWN. Be careful, the IAC will break easily. It is aluminum.

You can remove the IAC to clean out the passages in the TBI, but use care, the IAC can turn very hard and you could damage the IAC removing it. I do not suggest unscrewing the pintle (plunger). If you don’t get in back in far enough, the IAC can get damaged if the “pintle” (plunger) bottoms out in the TBI, when you screw the IAC back in.

Usually the IAC does not go bad electrically, but it is common for them to stick and stop moving.

If the IAC sticks as does not move as it should for each pulse, the IAC count will get off because the computer does not know the actual position of the IAC, but the ECM tracks the commands it has sent to the IAC and assumes it has moved every time it has been sent a pulse.

[chevymotocross]

Thanks Chionos. I know where it's located. I just have to buy some electrical safe TBI cleaner since all I have here is old carb cleaner and it says right on the can not recommend for EFI.

I'll post up how it worked!

[Chionos GMs]

Good Luck

[Hair]

Well???... How did it work??

[muthstryker]

I have the same problem, I started freaking out at first.

[Chionos GMs]

Originally Posted by Hair

Well???... How did it work??

X2