2.5L ('98-'01) P1506 code Idle Air Control Overspeed error

[Matt Black]

Hello folks! I have a 1999 XLT 2wd 2.5L 5speed manual. Truck has been sitting for probably 5 years. Recently got it back on the road and I'm working through the various codes and issues. Check engine light came on and a scan showed a P1506 code, Idle Air Control Overspeed error. I pulled the IAC and began cleaning it with MAF sensor cleaner I happened to have laying around but before I reinstalled it I saw where you could test the unit by checking resistance. It failed the check so I just purchased a new one. A quick test run around the block seemed to indicate that the issue was resolved but on the next startup, it immediately idled very high and the check engine light came on again. After 5 seconds or so the idle slowed down but the light remained on. I ran to the post office and when I started the truck to head back home it idled high again, but only for a couple seconds before slowing down. The check engine light remained lit. I have not rescanned so it could be a new code, but with the fluctuation in idle speed, I figured it was related.

I had the negative battery cable disconnected for the duration of the time I was replacing the IAC, probably well over an hour while I cleaned and checked the old one and then went to the parts store to get a new one and get it installed. I'm hoping this is just the computer adjusting to the new sensor, but figure I'd check here just in case there was something else I had to to clear out any bad mojo?

Thanks in advance for any suggestions!

 

[-Nate]

I had this same failure and used a DENSO brand IAC valve, no codes and it flew through the emissions test but some times it takes too long (IMO) to return to idle speeds .

Subscribed to hopefully learn from answers here .

 

[rubydist]

My experience with cleaning iac valves is that even if you do get them to free up and work correctly, they very soon get sticky again and don't work right. I have also had new ones bad out of the box. Most likely it needs to be replaced.

However, you might also have a vacuum leak that is intermittent, so check for vacuum leaks also.

 

[Matt Black]

Thank you for the replies! Since I replaced the IAC valve the idle seems high right after starting the truck but almost immediately settles down to an acceptable RPM. Oddly enough, there weren't really any idling issues that I noticed before I replaced the valve, I just did it because the check engine light came on and the code said it was the IAC. The resistance for the IAC tested out of range so I installed a new one. I was hoping the light would clear by itself after driving the truck and letting the computer adjust to the new sensor but I've been driving it for a couple weeks and the check engine light is still on, so I just disconnected the NEG battery cable and I'll leave it off for an hour or so just to hopefully clear out any codes and see if that does anything.