IAC woes

[Nelso90]

Hey guys,
I have a 98 ranger stepside 4x2 with the 2.5, and I am having the damnedest problem with a high idle condition. I did have a scan tool, but it didn't catch the high idle as it happened, it wasn't loaded on the right program. At any rate, here's how it works:
I am driving in 3rd or 4th, and I get into it, sometimes WOT, sometimes not, and then I back out of it gradually. The truck will feel like it's engine-braking for a second, then there's a small nudge forward and engine braking is gone. I put in the clutch, and revs go up immediately to 3000. As I'm thinking wtf is going on, I stop the truck. I am downshifting and the high idle condition remains. Once I stop, usually a little before, or sometimes the instant I stop, idle returns to normal. I have replaced the IAC, and I have run a test on it with the scan tool, and it's responding just as it should when I vary the load on the engine at idle. I looked at EGR duty cycle, IAC duty cycle and TPS voltage as well, and they all seem to be responding. EGR gives kicks to 40% when I blip the gas, and TPS didn't seem to be hanging up anywhere. This is a transient condition, and the whole idle dropping as I stop makes me think it's a condition with the PCM, as that's tied into the speed sensor. I am thinking it could be part of a TSB, as there are a couple of TSB's out there dealing with high idle conditions, however I have a sticker that says there was an authorized modification done to the truck by a ford dealer. I called ford and asked them to see if the recall had been done based on my VIN, and they couldn't find anything on it.
I figure if I take it into a dealer, I want them to reflash my PCM. At $80/hr, I do NOT want them trying to replicate a problem that may not appear, especially when I had a senior in the Automotive program here at Minnesota State ride with me and verify that something wasn't normal!

Do you guys have any thoughts? I'm at wits end, if I had an OBD-II port on the side of my head, I'd plug it into my truck and fix it myself!
Thanks
Mike

 

[Bryan22]

have you checked for vacuum leaks?

 

[greenpus]

Pretty common on these 98-2000 2.5 engines. The TPS connector is jacked up. Ford makes a kit that splices into the wire harness to replace the TPS connector but fug that. Because of this issue you'll replace the IAC until you're blue in the face and your problem won't go away.
I fixed my issue by buying electronic spray cleaner and dielectric grease. I popped both connectors off the IAC and TPS and hosed them down with the electronic parts cleaning spray. Make sure you get the spray that does not have any lub in it. While the connectors are still wet with cleaner, connect them back up and take off again. Do this several times so you get all the corrosion off the male and female connector. After doing this several times to make sure the connectors are clean. Let them hang loose until they are dry. Once dry, stuff connectors full of the dielectric grease and then reconnect.
Because of this process your Idle trim might be screwed up. Which means your idle may fluctuate a little. Ignore it and drive your truck for a few days making sure to do both highway and city stop and go driving. The idle trim will fix itself.
Good Luck!!!!!!

 

[Nelso90]

Alright, I can give that a try. I've gone through the IAC connector, but I can do it again a bit more thoroughly, but I've never gone through the TPS, so that might be something I should do.
Any other suggestions if that doesn't work? I'd go out and try it now, but it's finals week, and I need to study like crazy!

 

[Nelso90]

I should add also that the truck is throwing a P1000, because I disconnected the battery to try and "clear out" anything in the PCM's memory. Needless to say it didn't work, but could that be screwing with my idle too?

 

[Nelso90]

I have yet to put dielectric grease in the connections (I have that at home), but after a thorough cleaning, everything seems to be okay. I really appreciate having you guys around. I figured it was electrical, it ran great when it acted normal, but ran like piss when it didn't. Kind of an on/off thing, but I am terrible at electrical troubleshooting. I'll post again if it doesn't work out in the longer term.
Thanks guys!