Hi guys..as always short and sweet. 2002 F150 with 148K miles. Out of the blue, but getting worse, will go to crank, idle shoots to 1200 then drop and die. It will keep doing this until I put my foot on gas while I crank. Idle will bounce around when first crunk (giving it gas to keep it running), but once it is steady, truck runs fine, mainly on start up only.Hooked up my DTC reader..no codes, IAC ??? It is original with the truck. Thanks.

 

Yes, sounds like it is your IAC. You can either take it off and clean it or buy a new one. If you decide to just clean it, there is no telling how long it will be before it acts up again. If you decide to buy new, I would recommend replacing it with a Motorcraft one. I replaced mine a couple of times from the local parts store and they didn't last very long at all. Went back to the Motorcraft IAC and haven't had a problem since.

 

Thanks Buck, gonna try brake cleaner first, if still doesn't help, I found the Motorcraft CX-1789 on ebay for $85.

 

No, do NOT use brake cleaner. Use WD-40.

 

Thanks, I used WD 40 to clean , reinstalled and truck started and settled nice on 800 rpm. Shut it off, restarted and it hunted for idle again surging up and down (at least didn't die), so I went ahead and ordered a new Motorcraft piece. Thanks guys

 

Rock auto has the motor craft one pretty cheap. If its me I clean the throttle body while I'm at it with THROTTLE BODY cleaner.

 

Great minds think alike lol, I ordered a MotorCraft IAC for $85, and went to Wally World asd got a combo pack TB/MAF cleaner while I am at it. Thanks!!

 

This is only for information as you cannot fix an IAC that acts like you describe.
They actually do not wear out but have a dash pot function built is that you cannot get to being the housing is crimped together.
A dash pot function is a slow down action in one direction.
For this to happen there needs to be a diaphragm to hold air or vacuum once the electric solenoid operates.
The diaphragm is spring loaded to close when the electric signal pulses are reduced.
The diaphragm has a very small hole to regulate the dash pot action.
If the hole gets plugged with dirt or carbon, that function stops or is interfered with.
Hence the motor 'normally' starts with an open IAC (high idle) then cannot close under proper control.
The result is stalling.
More than you really wanted to know but that's what is going on.
It would be interesting for you to take it apart and verify the hole opening.
Good luck.

 

Great info bluegrass, I like knowing how stuff works, for you I will cut open old one with Dremel...do I cut length wise or one end??

 

Just behind the crimped metal tube.
Good luck.

 

Thanks, I will cut open and post pic

 

I got in a new MotorCraft IAC, pulled TB and cleaned along with MAF, K&N filter and IAC sensors

Before:



After:



Also, at the urging of Bluegrass, I cut open the old IAC, there IS a tiny hole in there and on one end you could see carbon deposit, as well there is a rubber diaphragm that could get a pinhole in it







She once again purrs nice and smooth

 

You got her.
Good luck.

 

so whenever I start my truck after the engine is warm, it will start right up but then the Rpms will drop and go back up then drop. The best thing I can relate it to is when you almost stall a Manual and it kinda struggles to stay running. It does this for about 2 seconds then it will generally run fine. It's a 2006 f150 4.2 v6. Looking at some of the stuff you've posted and replied too I thought you sounded like you know about this problem. It doesn't throw an engine lights either

 

Wrong forum, my friend - you have a 2006 which uses an electronic throttle. This thread is in the 1997-2003 forum, those trucks have a throttle cable and IAC.