High idle and P0505. IAC seems functional

[jcush87]

So my truck has idled at about 1400-1500 when warm since I bought it about 5 years ago.

Recently I tried to shoot carb cleaner down the hole in front of the butterfly valve in the throttle body in order to clean the IAC. This resulted in no change.

A week later I get the CEL and P0505 which is Idle Air Control Valve Control Circuit.

Today I took the throttle body ff and removed the IAC. I cleaned it all up, but it wasnt that bad. I checked the IAC solenoid by hooking it up to a battery, the valve moves freely.

reassemble it all and there is no change.

If I unplug the IAC cable my idle drops down to 800-1000 instead of the 1400-1500. That is nice, but when I am driving and let off the gas the car abruptly loses speed (Like a tap on the brakes)instead of gently settling. And if I use cruise control it drives rough where it will surge then stop surge then stop, each time it stops it is abrupt.

Anyone have any ideas? Is the ECM sending the wrong commands to the valve when it is plugged in?

 

[bishopTS]

remember the cables for throttle and cruise shouldn't have tension on them. if your idle is being controlled by the tension on your throttle cable it's too tight.
also check for vacuum leaks while it's running with a squirt bottle of water. it will make a slurping sound where it's leaking and is not as harsh on your o2 sensors as carb cleaner is.

 

[SparkEE]

The test for the IAC per the FSM is to check resistance across the terminals. I can't remember off hand which terminals and what the reading should be though.. I had the same issue and when I finally checked the resistance it was out of the range from the FSM. I put in a new one and the CEL and high idle were gone. You may want to give that a shot.