Idle Air Control (IAC) valve

[MTMike]

Anyone had any experience with these, and their symptoms when they go bad?

My wifes truck is idling funny.... I.E. coming up to a stop light and pushing in the clutch, the engine idles at 1800-2500 rpms for about 5-10 seconds before dropping back down to normal... and between gears while shifting, when the clutch is in the engine idles at whatever speed the clutch was let out at until you put it into another gear and engage the clutch or let it slowly idle down.

I actually successfully got it to drive it self in 2nd gear at 20 mph without touching the throttle.

I consulted my Haynes manual and I narrowed it down to 3 possibilities. Throttle Position Sensor (TPS), IAC Valve and a sticking throttle linkage. The TPS sensor checked out ok, and the throttle cable wasn't sticking.

I guess my question is, is there any other thing that can cause symptoms like this or is it most likely the $75 IAC valve?

Oh, sidenote. I tested the resistance across the 4 pins of the IAC valve like the manual said to, and it says in the manual "If the resistance across A&B or C&D is 40-80ohm, its good.. if it's open (IE infinate resistance, no movement in the ohmmeter) then replace the valve" The resistance across A&B and C&D on Dawn's valve is 0... like it's shorted. It pegs the ohmmeter.

Thanks!

-Mike

[hockeyman]

Man! My car did the same thing when my IAC went bad! I would lightly touch the gas pedal, and the throttle would go up to 3k rpm's for about 7 seconds. As I was driving abouve 30 mph, it would be fine. The idle would only go haywire when I was either at a stop, or traveling below 30 mph.
Contact Autozone for the IAC Sensor replacement. GM wanted $125 for my IAC, and autozone sold a new one to me for $26. Works great!! :D

-Marc

[MTMike]

<blockquote>quote:</font><hr>Originally posted by hockeyman:
Man! My car did the same thing when my IAC went bad! I would lightly touch the gas pedal, and the throttle would go up to 3k rpm's for about 7 seconds. As I was driving abouve 30 mph, it would be fine. The idle would only go haywire when I was either at a stop, or traveling below 30 mph.
Contact Autozone for the IAC Sensor replacement. GM wanted $125 for my IAC, and autozone sold a new one to me for $26. Works great!! :D

-Marc<hr></blockquote>

After talking to Russ I've detirmined that it is for sure the IAC.... cheapest in town is $75. Found it at autozone.com for $63 (this is for a 4.3L Vortec, keep in mind - not a 3.8L)

I'm gonna call the junk yards in town tomorrow and see if I can locate one for in a wrecked S-10, Blazer, or other 1/2 ton truck with a 4.3L Vortec for $10-20.

Thanks for the response!