Once again I come for help. My car all of a sudden developed this problem. I was driving to the gym all of a sudden the idle shot up . When I turn the car on the idle races up to 2200 and stays. Then when I shift it bangs gears obviously. The idle did fluctuate once it idled at 1500. But for the most part when I turn it on it starts idling at 2200 and only goes up. I have looked for vacuum leaks and found none, I know it is not the TPS. The throttle body plate is closing plus the linkage seems to be fine. What I did find was the IAC valve is not sealing correctly. I can easily blow air past the valve, the piston stops about an 1/8" from sealing the chamber. Think its the IAC?
Iac Question
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dj_jace
Active LVC Member
I'm also wondering about this. I think my iac is going bad also. My rpms drop sometimes at red lights when I'm coming to a stop and then also sometimes when I first start the car my rpms will shoot up to 2k but then after a minute or so come back down to normal. I've read a few places that the iac can be cleaned but my brother is an auto technician and he said to just buy a new one. Suggestions?
joegr
Dedicated LVC Member
Joe I know you helped me before big thanks. Does it sound like the IAC to you or a vacuum leak? When My iac is in my hand its open all the time. I could try jamming it closed and reinstalling it to see if it makes a difference. Is the IAC normally closed with no power on it?
joegr
Dedicated LVC Member
I've never looked at a gen I IAC (gen II doesn't have them). I've looked at, cleaned, and replaced other Ford IACs. I don't recall how far closed they were at rest. I do know that the ones I had normally failed closed, but later they redesigned them to have a little stop that kept them from closing all the way. This was for the 4.6L engines back in the late 90s, so it may or may not apply here.
Well after a bit of research this is what I found. I stumbled across a TSB from ford about the IAC. Failure of the device can cause low idle, rough idle, high idle, surging or no starting. Also it is possible what a fault code will not been generated. I believe the IAC is normally closed. The pcm must open and close it to maintain idle etc. Mine was open all the time. Even with the throttlebody closed with the IAC open the engine was sucking in alot of air which should cause it it idle too high. I have the part coming in from Rock Auto so we shall see.
xCloud_Ambition
LVC Member
damien_nitez
New LVC Member
Hello all! I'm experiencing some of the same issues as listed above on my 01' LS V8. I've replaced the IAC but, I'm still having the same high/low/rough idle. Could something else be the cause?
joegr
Dedicated LVC Member
Yes, several possibilities.
Marginal/bad COPs - recommend replacement of all COPs (coils) and spark plugs if you haven't done that already.
Any kind of air/vacuum leak on the intake.
Loose fuel injector connectors.
Clogged cats.
Bad/dirty MAF.
...
Is the check engine light on? If so, what are the codes?
damien_nitez
New LVC Member
Sorry it took a while for me to get back to you guys. Yes, the check engine light is on. I just pulled the codes a minute ago and found two more on top of the initial one I was getting.
P1504
P0102
P1507
P1504
P0102
P1507
joegr
Dedicated LVC Member
P1504 - You have a fault in your PCM, shorted or open wiring between the PCM and the IAC, or an electrical problem within the IAC.
P0102 - Problem with your MAF, looks like an electrical problem
P1507 - Just means that the PCM can't keep idle speed high enough because of the problems that you have.
P0102 - Problem with your MAF, looks like an electrical problem
P1507 - Just means that the PCM can't keep idle speed high enough because of the problems that you have.