Bad IAC Valve?

[zleepr1]

I'm new to this forum and the wealth of information here is amazing! I have a turbo tweak street chip version 5.6. I'm running 100 octane. The car (tta) is stock with the exception of the chip. I just purchased a scanmaster and am trying to fix the rough idle. The car would idle really rough when cold. I needed to keep my foot on the gas to keep it running until it warmed up. The IAC was at 175. I adjusted it down to +/- 40. However after I drive the car to warm it up and then re-start it the number starts at 40 drops from 40 to 0 (quick increments). When it's cold it still reads really high >150. My TPS is set at .38 idle and 4.54 WOT. The car has 12,000 miles on it. I haven't taken the IAC valve out to inspect yet. Could it be a bad IAC valve? My AF number is 5-6 at idle. Int and BL are at 128. This chip idles in open loop so I'm not sure if that has something to do with my readings.

Any thoughts?

 

[dennisL]

Your TPS at idle is too low and you can't adjust the IAC while the engine is cold or during warm-up. It must be hot (coolant above 150 degF). If you do remove the IAC for cleaning, or just want to make sure the IAC is tracking properly prior to adjusting it, you can manually reset it.

You can manually “reset” the IAC by performing the following:
1) Jumper ALDL connector pins A and B. (top right two pins)
2) Turn the ignition on but do not start the engine. The ECM sets the IAC count to zero. Wait 30 seconds so the IAC has more than enough time to seat the pintle. Leave ignition on.
3) With ignition still on, disconnect the IAC electrical connector. (Be careful, not much room.)
4) Turn the ignition off, remove the ALDL jumper, and reconnect the IAC electrical connector.
This establishes the seated or zero reference point.

Start the engine and let it completely warm-up. Make sure A/C is turned off.
Check the IAC count at hot idle for 10 - 40 (20 - 25 is ideal). Adjust the Min Air Adjust screw to get within the range.
Turn the screw in VERY small amounts (1/4 turn or so) while making this adjustment. Turning it counter clockwise closes the throttle blade and will raise the IAC count. Turning it clockwise opens the throttle blade and will lower IAC count. Be sure to allow the car to "settle" a bit after each adjustment for a few seconds.



Once you have IAC counts within your target range, check/adjust the TPS for 0.42V ignition on, engine off.
Lastly check the IAC count again, since they interact.

 

[zleepr1]

Thank you for the information. The coolant reading was 180 when I adjusted the IAC. I will try the manual reset procedure. It seems as though the ecu is trying to control the IAC count but is not getting a response.