engine code p1506

[thomas weldon]

i had problems with stalling and then no start, no engine light came on. i replaced the iacv and the engine started and ran fine, but then while deer hunting the engine idle went to 1500 rpm's and the check engine light came on. code is 1506 any help will be appreciated. 01 s/t 4.0 liter. thanks, tom.

 

[Todd Z]

From the FAQ section of the site

Could also be a miss adjusted throttle body, or a bad TPS



P1506 - Idle Air Control (IAC) Overspeed Error This DTC is set when the PCM detects engine idle speed that is greater than the desired rpm. IAC circuit short to GND

Damaged IAC valve

IAC valve stuck open

Vacuum leaks

Failed EVAP system

Damaged PCM

Disconnect IAC valve and look for little or no change in engine rpm as an indication of a stuck or damaged valve.



From the FAQ section of the site

 

[thomas weldon]

thanks todd. i will start with unhooking the iacv and go from there. tom.

 

[Kevin Palmer]

By unhooking the IAC I think they only thing you will learn is to see if the IAC is operating.



If you unhook it, I would expect your Trac to stall as there is nothing to control the minimum RPM's. If something is allowing a vacuum leak, then there is a good chance it will continue to run as the IAC is basically a controlled vacuum leak.

 

[Dre L]

Try to let out the idle speed set screw which props up the throttle valve. You want to lower it so it closes the butterfly valve a bit. It takes a few tries with VERY SMALL ADJUSTMENTS. You want to hook up a digital tach (like that on a scangauge) so that IIRC your idle is between 650 / 700 in park at normal operating temperature with no A/C on. Once you've got it about there, disconnect your battery for a minute or so, reconnect and recheck the idle speed. Go through the re-learning process in the manual.



My bet is that the IAC was dirty / malfunctioning, someone fudged with the screw, you replaced it, whoosh more air.



I had this happen to me because my IAC and air filter were dirty, I fudged with the screw, things were cool, I cleaned the IAC, filter, and TBI, all was cool, went for a drive and bam CEL for overspeed.

 

[thomas weldon]

thanks for the input. i unplugged the iacv and the rpm stayed up around 1500. i then gave the old one a really good cleaning while i watched the lions stick up the place. i think the lions need their iacv replaced. i put the old one back on and poof the old girl started and ran at normal rpm. i am going to get my money back on the new (defective) iacv and order one from ford's. maybe old man ford will be able to afford a new coaching staff and gm, lol. tom.