98 f150 iac code 1506

tomlew80 · #1 12-28-2004, 09:01 PM

Was hope for some help...
I have a 1998 Ford F150...4.6 motor
I cleaned the throttle/butterfly area with intake cleaner...then went to drive the truck..The idle was around 1050 in park...had a code ..po1506 ..idle overspeed fault...I then replaced the IAC and proceeded the drive the truck so the engine will relearn the idle process...the check engine light did not come back on but the idle still seemed a bit to high...I'm I doing something wrong here?????? I NEVER had a problem like this just from cleaning the throttle plate!!!!....does anyone have any ideas?????

PLEASE help..if possible..
Tom

Johngs · #2 12-28-2004, 09:17 PM

how high does it idle now?

how did you clean the intake? Did you remove it and clean it?

tomlew80 · #3 12-28-2004, 09:29 PM

hi John..
thanks for your reply!!!
I've been going crazy with this problem...

I took a tiny bit of intake cleaner and a brush...cleaned the butterfly area while the throttle was on the car...then the code came in and the idle was higher...

I last drove the truck this afternoon...the idle in park appeared to be about 1000...

I hoping the relearn process just needs to be done..I diden't hear back from the owner so I guess No news is good news...but I would like to find out info for my own knowledge

tomlew80 · #4 12-28-2004, 09:41 PM

just to add a bit of info...

The truck ran pretty decent when it came in...I noticed the throttle plate was carboned up...that's when I decided the clean it out...from there all the problems started...check engine light on...code 1506 IAC overspeed fault...relaced the valve..cleared the codes the drove the truck however I did not disconnect the battery...WOULD THE COMPUTER STILL PICK UP THE READINGS OF THE OLD VALVE???? ....I then disconnected the battery and drove it again...the check engine light did not come on but the idle was still a bit high...about 1050+ in Park 850-9 in drive...

Ant Ideas?????

Johngs · #5 12-28-2004, 10:34 PM

well, the idle is definitely too high...it should be under 800 when warm.

I would say try disconnecting the battery again (remove the neg battery cable, turn on the headlights for ~10 minutes), but make sure you let the truck idle for about 10 inutes when you reconnect the battery before you drive it.

Other than that Im not real sure (and I kind ofdoubt this will fix your problem but its worth a shot).

tomlew80 · #6 12-29-2004, 07:33 AM

just heard info regarding this truck....
the idle has seemed to come down a bit...however the check engine light has come back on...I will have to check it on the computer again to see if the same code has returned...

I have be an auto mechanic for 16 years and have NEVER come accross such a situation!!! This one seems to baffle everyone I speak with....

Thanks for your input!!!!! At this point I'll try anything!!

More to come....

hcmq · #7 12-29-2004, 04:35 PM

My guess is that you messed up the positioning of the throttle plate when you cleaned it. Did you just use your fingers to hold it open?

Also, did you run the engine while cleaning it?

The IAC usually causes a low idle concern.

Do what johngs says and disco the neg cable then turn the lights on. after 5-8 min turn the lights off then recon the neg batt cable start truck and don't touch the gas when starting and let idle for 8-10 min then you must drive it for atleast 20 min after that.

remeber codes are for where to start a diagnosis not for what sensor to replace.

good luck-

tomlew80 · #8 12-29-2004, 06:25 PM

Thanks for all the info!!!

I'll be looking at the truck again the end of the week...
I'll try disconnecting the battery/headlights on..etc...

Do you think It is possible that carbon was disturbed down lower in the intake????? causing a problem...

Tom

tomlew80 · #9 12-29-2004, 06:30 PM

had the engine OFF while cleaning...
I used a soft brush to lightly clean the surface..
and I held it open just by holding the linkage..never had my fingers anywhere near the plate area...

these seem like all logical explanations...I'll look into each of them..
Thanks!!!

Green_98 · #10 12-29-2004, 06:32 PM

98 4.6 73,000 miles:

i took my IAC/throttle body/EGR valve completely off this last weekend and cleaned both completely out. Lots of carbon build up. After I got them all back on and a new battery in my truck, my truck idled high too for about 50 miles or so, then it settled back down, but still runs a little faster and "peppier" then before i did the cleaning
Im thinking that if you unhook your negative terminal, turn on the headlights for a while, then turn them off and re-connect your battery, your truck will settle back down. You might also consider doing this throttle body cleaning to your truck,it's amazing how much better your truck will run after all the carbon is cleaned out.

If interested, check out my thread on "rough idle" on page 2 in the Engines forum.