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Wrenchtech, ASE Certified Technician
Category: Chevy
Satisfied Customers: 1403
Experience:  40 years experience with ASE certification as Master Technician with L1--Repair Shop Owner
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94 GMC Suburban K1500 Idle speed problem

Resolved Question:

My 94 Suburban, 130K miles has an idle which will "droop" and recover while sitting at a stoplight in gear once in a while causing it to stall. It will also "droop" while in Park but not as noticeable and does not stall. There is no MIL light and my Auto Xray scanner does not pick up any faults.
Submitted: 8 years ago.
Category: Chevy
Expert:  Wrenchtech replied 8 years ago.
Did you replace the IAC?
Customer: replied 8 years ago.
Yes I replaced the IAC and went thru the "learn" procedure.

Expert:  Wrenchtech replied 8 years ago.
Did you scrub down the inside of the throttle body when you did that?

Customer: replied 8 years ago.
As it was a few years ago, I don't think I scrubbed the throttle body bore...Do you mean with Carb Cleaner and a toothbrush? Or is more dissassembly required?
Expert:  Wrenchtech replied 8 years ago.
When did the problem start?
Customer: replied 8 years ago.
I've had this problem since I purchased it used in 1999. It has been a nagging little problem that I have been pecking away at....Never a problem at cruising speed..
Expert:  Wrenchtech replied 8 years ago.
The idle is controlled by the amount of air being let into the intake at any time. With the throttle plates completely closed, the only air supposed to be allowed in is through the IAC so if the idle is erratic, then the air flow in is erratic.

The first thing I would do is scrub down the inside of the throttle body with some carb cleaner and a tooth brush. Check the rest of the engine over real good for any vacuum leaks.

If you still have the problem, you want to get your hands on a scan tool so you can monitor the sensor data and look for any glitches in things like the TPS, CTS, MAF, IAT etc

Lastly, I wouldn't rule out a problem with the IAC wiring or computer. While your monitoring the sensor data, look at the IAC and see if it's moving when these symptoms occur
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