I have came up with the code P1506 on my 2002 f150 4.6 v8, it idles at 1.5k rpm and goes down to 1k on drive and reverse then back to 1.5k on neutral. I am stumped on this problem because i don't think it could be a vaccum leak. If i discconect the Iac while truck is running, nothing happens? could that mean a bad iac valve?. If so, i went to advance autoparts, Autzone and both are missing the vacuum line . Thanks

 

Did you remove the IAC valve when you were cleaning the TB? Being it does nothing when you disconnect it, I would replace the IAC valve.

Also, re check all of your vacuum lines

 

The 1506 code is an over speed error that just confirms your issue.
The IAC is stuck open same as giving the motor throttle from the cab.
Remove it and check the internal pintel for free sliding against it's spring in the solenoid housing.
It must be closed normally and free to slide open when the computer applies 'pulses' to control it's opening actions.
If the computer cannot control it, the idle will not be controlled for cold starts, hot restarts or any normal drivability and even result in pushing you at a stop when you don't want it..
Good luck.

 

If it is the Air control valve , i cannot seem to find the same one as mine. None of the ones i see have the vacuum line connection. Has anyone had this problem.

 

no Vacuum leaks that i can detect. The IAC valve spring moves up and down.

 

Could it be the Throttle Positioning Sensor if it is not the iac

 

Get a new IAC. The TPS rarely fails. What chemical did you clean with? could be you used something to strong and it killed the IAC. pretty sure thats what the code is telling you. Supposed to clean the IAC gently with throttle body cleaner and then lube it with WD40

 

It's time to start over again.
Try to understand:
The TPS does not control engine speed in any way.
It is a variable resistor that signals the computer what the throttle plate opening is, how fast throttle plate is opening so extra fuel can be supplied, general fuel control in conjunction with the mass air meter and what to do with upshifting and down shifting load points.
From this signal many operations are affected. None is engine speed directly.
.
IAC is an air 'bypass' around the throttle plate used to control idle speed only.
If you remove the electrical connector and no idle speed changes, the IAC is NOT working, the connector is open or or there is a large air leak at some other point allowing more air in than the IAC can close down and account for.
This is all there is to it. Re-read this until you get the operation of each part.
There is no-where else to look.
Is the throttle cable stuck off rest for some reason?

Good luck..

 

Thank you

 

guys ive replace the iac and the problem is still there. Ive noticed that the rpms bounce 1.2k-1.4k on idle. I disconnect the tps and it idles up to 2k and stays there until i connect it back? I am stumped. No vac leaks either .

 

The next step would be trouble shooting connectivity of the IAC.. Loose connection some where.

 

The TPS has nothing to do with the idle.
What you did by disconnecting it is an illegal see what happens condition that leads you no where..
The IAC is being held open (or) there is a leak at some point.
Remove the connector off the IAC with motor running.
If the idle drops, the IAC is being held open from a trouble condition such as a ground or cross in the harness, not an open circuit.
Unpowered, IAC is always closed unless it is stuck open.
Good luck.