Hello all. I have a 1997 Ranger with a 3.0 v6 with a super high idle.

It idles at 2500 RPM when the IAC is plugged and a steady 1100 when un-plugged. I have replaced the IAC twice now (dropped the first replacement. long story) and and have also checked for vac leaks with no results.

After about 2-3 minutes of idling at 2500 on a cold start it will drop down to 1100 (same as when IAC is un-plugged), but after a 10 minutes or so drive it will idle steady at 2500 with minimal if any dropping in RPMs. This is driving me crazy not only because it sounds horrible but also because of the fact it's burning through fuel like it's going out of style.

I have checked the MAF sensor and it looks brand new (not the original owner) along with the O2 sensor. I have been meaning to check the TPS voltage to see if it's working correctly but without a working multimeter it's making it difficult to do anything.

I'm at a loss with this right now and because of all the previous repairs i have done to it and the others that still need to be done i don't have the biggest budget to fix this problem nor the money the truck is using in gas.

Any suggestions would be greatly appreciated. Thanks

 

Does the engine stumble and die or at least barely idle with the TPS unplugged or continue running with a high idle?

Josh

 

It continues running high with the same symptoms as if it were still plugged in but 100 RPM lower than when plugged in. Could it be the PCM/ECC failing? I can't think of anything else that could cause this except for maybe the idle screw but that would keep the RPMs high if it was adjusted incorrectly right?

Thanks

 

I would venture to say the stop screw is turned far too much. The engine should either barely run at idle or sputter and die with the TPS unplugged. The IAS is what actually compenates for the air at idle and not the throttle blade like a carburetor.

It certainly couldn't hurt to back the screw out until the engine barely runs and go from there. Keep track of how many turns you do just in case in needs to be reset to where it was.

Josh

 

Thank you for the quick reply.

Thats a great suggestion that i never even thought of. I'll try it and let you know what happens.

Thanks

Edit: No difference at all. The screw was actually backed off all the way like the previous owners had already tried that.
Any other suggestions? I'm drawing a complete blank on what could be causing this.

And the weirdest thing that's really getting me is the fact that when the IAC is unplugged it idles like it's supposed too when it should die from no air getting into the engine. But with the IAC plugged after 2-3 minutes of a 2500 RPM idle it drops down to that 1100 RPM "Normal" idle range that it's at when the IAC is unplugged. This makes absolutely no sense to me at all.

 

Did you look at the TB throttle plate to see if it is closing all the way? Something, like the TPS, might be preventing it from closing.

Check the PCV elbow too, the stupid thing cracks all the time.

Normal hot idle should be 800-900 RPM.

Josh

 

Edit: Welcome to FTE!!!!

Shurely you have a CEL lit & or computer trouble codes stored, so scan, or have your favorite autoparts store scan the computer for trouble codes & post All code Numbers found, as they can provide good trouble shooting clues. Most autoparts stores will scan for codes at no cost if the CEL is lit.

 

The TB plate is shut nice and tight with no gaps that i can see.

PCV elbow is perfect and i actually took it out a couple weeks ago and cleaned out the gunk that was in there that was preventing it from operating at all. Just checked it and its nice and clean like i just got finished cleaning it.

Thank you for the welcome and your suggestions but i have no CEL on at all and never have. The only light that is on after starting up is my parking brake light but that's only on because i screwed with the brakes and the cable before i found out the parking brake struts are missing.

This is really starting to annoy me that nothing i try is working. I first thought that it might be an intake leak but i feel no suction at all and have also done the carb cleaning test with no results.

This is probably the only thing that has so far gotten the best of me in being unable to fix.

Edit: Alright new problem. As i was messing with some vacuum hoses i happened to look down at the ground below the engine and noticed some green. So i crawled under the truck and saw it was antifreeze that was collecting on the bottom of the bell housing. Thinking this and the high idle could be caused by an intake leak i looked behind the engine but didn't see anything so i then i looked at the freeze plugs and noticed one on the driver's side was pretty bent up but couldn't tell if it was leaking at all due to all the oilish reside on that side of the engine. I did a pressure test after putting in a new radiator but there were no leaks and it was holding the pressure.

Could this cause the high idle?

 

A vacuum leak will cause a high idle & from the rpm values you posted, you surely have something wrong, like a bad vacuum leak.

Check the PCV valve hose & the PCV valve itself. As has been said, if the PCV valve hose, or the valve itself is sludged up & not closing, it'll cause a vacuum leak idle problem.

When you go to KOEO, does the CEL light up for a self check????

"Pending" trouble codes can be stored in KAM that haven't happened often, or long enough to have the computer turn the CEL on, so if in doubt, have the computer scanned for truble codes & post the Numbers.

The coolant leak won't likely cause an idle problem, unless its from the intake manafold.

Edit: Did the high idle begin suddenly after some event????

 

Yeah a vacuum leak was my first suspect but as I said earlier I've checked all the hoses and connections that I can see and get my hands on and all are fine.

Also like I said in an earlier post I cleaned the PCV valve about 2 weeks ago because it was full of sludge and I rechecked today and its perfectly clean. The PCV elbow and hose both look fine as well.

When I turn the key to the "ON" position the CEL doesn't even light up along with half my other warning lights. Not sure what's going on there.

I'll see if I can get it down to autozone sometime this week and get it scanned.

It's had the idle problem since I've gotten it so it's nothing new.

Thanks for all the suggestions and help.

 

OK, the CEL may be burned out, or disconnected, but you likely have trouble codes stored in KAM, so don't disconnect the battery before you get it scanned, as that would wipe/erase the KAM & stored codes.

Well it seems a PCV system leak is no longer on your suspect list, but finding lots of sludge in it isn't a good sign that the previous owner kept scheduled maintenance up to date.

Other good vacuum leak suspects that come to mind would be the lower intake manafold or its gasket, vapor recovery system vacuum lines or fittings, brake booster or its vacuum line attachment, in cabin heater/AC control.

With the high rpm dropping some when you disconnect the IAC, suggests its working, but a vacuum leak, or throttle body, or plate problem, or adjustment exists, but you say you've checked them, so continue looking for other vacuum leak suspects.

Post up the trouble code Numbers found.

 

That's what I'm thinking. I tore a dashboard out of a 98 automatic ranger would it be possible to replace my instrument panel with the one from the dashboard? I also disconnected the battery for 10 minutes when I replaced the IAC but that was 1 week and 60 miles ago so I'm hoping the codes are back. Ill find out Wednesday when I take it to autozone. I have to return a muffler and pick up some intake gaskets so ill just do that while I'm there and get you the codes.

The connection from the brake booster is nice and tight didn't check the hose itself or the downstream connection but I will when I get back. I found some EGR system tests online that I performed and everything seems in good working order. The tests only tested the EGR valve and the DFPE sensor and not the EGR solenoid but I'm guessing that's fine if the EGR is working. My A/C is acting up and from posts I've seen I need a new blender door Anything else I should check out?

And i would hope the IAC is working since I've replaced it twice now but that's good to hear .

Thank you for all the help and suggestions so far. I hope I'm not annoying you at all.

 

The blend door is vacuum operated, so place its actuator & vacuum line to the in dash control & the line from the in dash control through the firewall to its underhood vacuum connection point on your suspect list.

Not certain, but I think the dash panel on the 98 will work ok in your 97.

Keep us posted on what you find.

 

Ahhh ok hopefully finding and fixing the high idle problem will in-turn help with the A/C problem then. I'll check all that out wednesday when i have some time to do more to the truck.

I do have some findings though. I was able to get my hands on a multimeter and followed THIS tutorial on testing the TPS. The readings i got weren't too surprising but also caught me off-guard a little. I back-probed the grey/white and the grey/red wires as told and with the throttle plate completely closed i got a reading of absolute 0 (key was to the ON position mind you). I then moved the plate steadily toward WOT and the reading didnt change in the slightest even at WOT. I even re-tested on each of the different voltage scales the multimeter had just to be safe but it was the same on each.

So now i know i need a new TPS not only for the high idle but also for the lack of power im getting and the bad MPG. I'll also be picking up some new intake gaskets (upper and lower) and see if i cant stop the coolant leak that has sprung up as well help even further with the idle and power problems.

I will keep you guys posted on everything that happens between now and whenever i can get this resolved.

Thank you guys for all the help so far

Oh and concerning the instrument panel: do you know of any way i can change the tachometer on the salvage panel to match the miles on my truck? Thanks

 

You aren't getting voltage at all TO the TPS? The TPS doesn't generate electricity it is just a poteniometer that regulates how much of the signal is sent back to the ECM.

If you aren't getting a reference voltage to the TPS there is a break in the signal somewhere else.

Josh