Fun with IAC replacement and fluctuating RPM

[drdoug]

Good morning,

I cant find the IAC thread so I am posting here.

I replaced my IAC on the 95 XLT. The felt filters were brittle and powdery. It appeared charred on the inside as well. Very dirty. It was an easy replacement for sure just had to make sure I had the right connector.

As soon as I started her up the RPM shot up to 2000. I let it stay that way for 30 seconds and shut it off because I wasnt sure that was supposed to happen but because of the new valve I thought maybe it had to reprogram.

I started it up and let it idle high for a minute and it started to climb down slowly. I drove around the block and it seemed ok. Awhile later I started it up and the idle was very rough dropping below 1000 to 500 or so. It did that this AM as well.

I drove it to the office this AM and it seems fine now although idle RPM is at 1200 for the most part. Previously it was 9-1000.

Does any one know.....Should the warning light on the dash go off by itself after the fix ?

BTW one shop that start with N wanted 140 bucks and AZ wanted 79 bucks. Don't wanna bash cos I use them both not sure if it is against etiquette to name names either..... but they are literally across the street from each other. 2x price.

thanks,

Doug

 

[XLTrunner]

I have read on other forums that after-market IAC's can cause idling issues with Ford vehicles. It's recommended to stick with Motorcraft. I installed a Hitachi from Rockauto (they claim it's the OEM issue) and, more than once, had to remove the plastic tray on top of the engine and give it a wrap with my socket wrench to get the idle to settle down on a cold morning...and, it's probably only got 20K miles on it. Could possibly only be a frozen condensation issue as the truck sits outside in the winter...but, annoying nonetheless.

 

[J_C]

If you're getting the check engine light, pull the codes. However i would disconnect the battery to clear the ECM and put it through a range of driving to re-learn everything, then see if the check engine light comes back.

Sometimes I wonder about new old stock, if something like the IAC ought to have a drop of light weight oil put on the solenoid shaft where it enters the bushing, moved that spring loaded shaft up and down slowly a few times, and left stood on end to soak into the bushing. I did that on my IAC when I cleaned it out last time... seen too many mechanical parts with bushings where the only problem was the bushing ran out of lubrication. That is, if you catch it before extra wear puts too much play in it, but you shouldn't have that situation yet with a new part.

By the same token, you might try cleaning out and lubing the old one, and find some scrap of felt somewhere to cut yourself a new filter for it, IF after trying it temporarily without the filter, it seems to be working better.

 

[lobo411]

My idle in-gear with A/C off is solid as a rock @ 750 RPM. I don't think it should drop below that without stumbling. My high idle first thing in the morning in park is around 900-1000 RPM.

Did you install the IAC with a gasket? If so, which kind? The "figure 8" rubber grommet, or the flat paper gasket? Mine came with both, so I installed both and haven't had a problem.

 

[J_C]

^ The first (only) replacement IAC I bought for my '98, didn't come with a paper gasket so I just installed with the rubber grommet and it worked fine for several years. Eventually it got dirty so I pulled the original out of a parts bin I'd saved it in, cleaned it out, lubed it, and put it on. I felt silly for not trying to clean it out in the first place, but I do recall that some people have cleaned theirs and that didn't work. Whatever.

Prior to putting it on, I did not remember there was the rubber figure 8 gasket so when I noted that places selling the valve itself were also selling a paper gasket separately, I made one by cutting it out of bulk gasket material, and put that on with the rubber figure 8 one still there.

That worked fine, then I took the paper gasket off and it still worked fine. I concluded that you only need the paper one if the rubber one is too disintegrated to make a good seal.

 

[koda2000]

I've replaced several IAC's on 2000/2001 5.0's. I bought one of eBay for about $22 (Chinese). I've reused IAC gaskets and never had any problems.

The ECU controls the IAC in an attempt to control the idle speed depending on coolant temperature. When cold the idle may start out at around 1000 RPM and within a few minutes will drop to somewhere around 650-700 RPM.

The IAC does not require any "reprogramming". It's just an dumb electronically controlled air valve. You will get a CEL if the ECU can't achieve the desired idle speed. The CEL may reset eventually, after a number of drive cycles, but it will stay on for quite a while. You can either erase it or disconnect your battery for 10-15 mins to turn it off.

Sounds to me like the IAC you purchased is defective, or you have a pretty good vacuum leak somewhere, which will raise the idle and cause the CEL to come on. Just because the CEL diagnostic says the problem is/may be the IAC, doesn't mean that the IAC is actually the problem. You can never take ODB II codes at their face value. They just point you at a problem, not the solution.