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Engine racing at idle


clockdore

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My 1994 Ranger was having idle issues, idling real high after AC replaced. I replaced the TPS sensor, and it's been fine for about a week. Then today, Started ok, went to the store and when I started it to leave, it's racing again. I got almost home and shut it off and started it again, it's worse. I was just watching a video about changing the ECM and there was mention of the idle air control valve. Could this be my problem? When they did the AC, the snorkel was split so he just taped it. If I unplug the TPS, it idles fine with the check engine light on. Will this hurt anything? Thanks.
 


rusty ol ranger

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My 1994 Ranger was having idle issues, idling real high after AC replaced. I replaced the TPS sensor, and it's been fine for about a week. Then today, Started ok, went to the store and when I started it to leave, it's racing again. I got almost home and shut it off and started it again, it's worse. I was just watching a video about changing the ECM and there was mention of the idle air control valve. Could this be my problem? When they did the AC, the snorkel was split so he just taped it. If I unplug the TPS, it idles fine with the check engine light on. Will this hurt anything? Thanks.
Your IAC could absolutly cause it to idle high. Plug the TPS back in and unplug the IAC and see if the idle changes at all. If it dont the IAC is stuck/failed.

The snorkel (guessing you mean intake tube?) could be an issue if the truck is MAF. As unmetered air is getting in past the sensor. If its MAP then it wouldnt matter but id still replace it just so dirt and shit cant get in.
 

clockdore

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Your IAC could absolutly cause it to idle high. Plug the TPS back in and unplug the IAC and see if the idle changes at all. If it dont the IAC is stuck/failed.

The snorkel (guessing you mean intake tube?) could be an issue if the truck is MAF. As unmetered air is getting in past the sensor. If its MAP then it wouldnt matter but id still replace it just so dirt and shit cant get in.
When I unplugged the IAC, the idle was already low. I'm going to replace the tube and the IAC, but I have to wait until Wednesday when I get my deposit. A new tube is $50+. I think I'll go t a u-pull-it and find one for a couple dollars. The IAC is $60+. It just seems odd that that part would go bad just when I had the AC worked on. I'm probably just being paranoid, but it's like it was swapped. But I found the bottom bolt on the IAC was loose, maybe that was it. I'll see this morning when I leave.
 

rusty ol ranger

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When I unplugged the IAC, the idle was already low. I'm going to replace the tube and the IAC, but I have to wait until Wednesday when I get my deposit. A new tube is $50+. I think I'll go t a u-pull-it and find one for a couple dollars. The IAC is $60+. It just seems odd that that part would go bad just when I had the AC worked on. I'm probably just being paranoid, but it's like it was swapped. But I found the bottom bolt on the IAC was loose, maybe that was it. I'll see this morning when I leave.
A loose bolt on the IAC would cause a vacuum leak and a high idle
 

clockdore

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This morning it idled fine from a cold start. On my way, the idle increased a little bit, then it was good when I got to my destination. When I started again when I left, it shot right up high then immediately backed down. It has been fine since. I think I'll just leave it alone for now. I might take it out and spray the workings with carb cleaner, being careful not to flood the motor. I read where that helps sometimes.
 

rusty ol ranger

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This morning it idled fine from a cold start. On my way, the idle increased a little bit, then it was good when I got to my destination. When I started again when I left, it shot right up high then immediately backed down. It has been fine since. I think I'll just leave it alone for now. I might take it out and spray the workings with carb cleaner, being careful not to flood the motor. I read where that helps sometimes.
Sounds like the IAC
 

clockdore

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After sitting for a few hours, I just started it to go to the car wash, it high idled for a few seconds, then backed down to the appropriate idle. It didn't race, just high idle, exactly what I would expect.
 

clockdore

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I'm curious. They had it in the shop for 2 1/2 days doing the AC. Why would they remove the IAC? It's not in the way. Either they removed it and overlooked the bottom bolt, or someone deliberately loosened it. I just can't figure it. It's a big shop, maybe four full time mechanics, maybe 5, specialize in AC. No matter, I think it's fixed, or at least I know where the problem is. Wednesday if it's still acting up, I'll replace it. Thanks for the help.
 

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It could have been loose... they bumped it while working on it and broke the seal.

If it's working now... I certainly wouldn't replace a factory part with an aftermarket replacement.

Even with a warm start... the idle flares up at start up. It should just quickly settle back in at Nirmal idle.
 

clockdore

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If it's original, it is 30 years old!
 

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rusty ol ranger

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If it's original, it is 30 years old!
I bought a new IAC for my 2.9 that was junk out of the box. Pulled the 37 year old one off my other 2.9 and its still on there lol
 

clockdore

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Excellent! This morning cold start, it was in the lower 60's, chilly for here, rpm shot right up pretty high, "oh oh", paused, then started creeping back down, stumbled once and almost stalled, then bumped it up a little. It's learning. Sat for a couple hours at the park, beautiful day today, started and idled perfect. I think it's a winner.

So, in the last month, had the ABS pump replaced, $160 part and $444 to have it put in. Ac has worked fine until this year, thought it was just the compressor. They said it had seized up and sent metal throughout the system. Replaced everything accept the lines and the evaporator, flushed them out, $1309. The guy that did it said he was pleased the way it came out, COLD COLD COLD. Got it out of the shop, went to the store, went to leave, click. Called road side service gave the starter a whack and it started. Starter $123+ and $110 labor. Then the idle problem, replaced the TPS, $50 So $2200 in the last month. But I love this truck, it's ideal for me. Had it for about 8 years. Looks almost new, been in Florida it's whole life. Hopefully it will leave me alone while I get caught up. I've had breaks all done, new shocks, new tires, all since I got it. Running and driving like new.

The rear main leaks of course. Would having that fixed be worth the expense? I've read no guarantee on that.

I've been reading other posts on here. You guys know everything! Good resource.
 

clockdore

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Acting up again.
 

clockdore

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I'm having the same issue. Worked fine until yesterday. I took out the IAC and sprayed the piston with cleaner, replaced the o-ring between the motor and the piston. Started up and idled fine. When to the store and when leaving, high idle. So I just took it out again and made sure everything was right. I spray the connectors with cleaner and I'm just letting it dry. My question is can that IAC be tested in any way? I have an OBD I but with no check engine light or anything I doubt anything would show. Stumped.
 

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