Fast idle when clutch engaged/coasting

[Rex2nr]

I have a 99 Ranger, 4.0 4wd with a 5spd. This started last fall but went away after replacing the TPS sensor. It is now coming back. There is no check engine light, but I don't have a scanner to check for pending codes.

It only does this when the engine is up to temp- the idle remains at 1900-3000 RPMs when slowing down, or coasting after slowing down from highway speeds. If I tap the gas, I can get the idle to settle back down to ~800.

Last fall I checked for vacuum leaks, found none. I cleaned the idle control valve, which made no difference. I cleaned the MAF, and replaced the TPS (I did get a TPS code at that point). Yesterday, I cleaned the contacts at the TPS and idle control after reading about this being an issue on the 2.3s, still acting up this morning. I also checked the battery/alternator. my battery was sitting at 11.8 (a bit low, but I don't think its too concerning) and the alternator is putting out 13.9 volts.

The other weird thing is that the oil pressure gauge clicks and jumps all over when I tap the gas to get the idle to settle down. When driving it acts normal, just erractic when trying to settle the idle.

Do you think I'm looking at a ground issue or voltage issue? It seems too coincidental and the only thing common is they are electric... i'm lost.

Thanks

 

[cp2295]

The oil pressure gauge and tps sensor arent on the same ground in fact the oil pressure sensor doesnt have a ground just a single wire. It says oil pressure is in the middle with 3 psi or more, and says u have none below that, u may need a new sensor there or your oil pressure is in fact bad.. Have u tried to warranty the part? Also try just unplugging the battery for 10 minutes or so and see if it helps.


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[Rex2nr]

I wouldnt think its an actual pressure problem since the gauge just snaps between zero and normal only when blipping the throttle when the idle is up.

Just ran out for lunch. When i started the truck it seemed to be idling high so i gave it a quick tap of he gas and the revs dropped to 800, then stalled.

192,8xx miles on her. Im kinda leaning now towards a bad idle control but i just dont want to start throwing parts and money at the problem blindly.

 

[RonD]

On the back side of drivers side head is a ground strap going to the firewall, check both ends, loosen and tighten, making sure there is good bare metal contact.

That is the ground for the cab electrics, all of it.
If it isn't a "good" ground the throttle cable can start being used as a ground, and "tapping" gas pedal changes it as a better or worse ground.
Seen it before so not just a guess, lol, long shot but not a guess

 

[Rex2nr]

I found the ground, the wire itself has some corrosion on it so I'll check that when I have some decent light.

I got back to work and unplugged the tps- no changes and unplugged the idle control- the idle levelled off but when I left work tonight the CEL came on and the truck kept stalling unless I gave it gas. I got the truck to autozone to pull codes- p1507 and p1504. I will read up on those next. I also reset the Pcm to see if unplugging the iac caused them.

 

[Rex2nr]

Cleaned out the IAC, its running better but the idle dropped to around 600. When i first started it it stalled out after running with a lope, but ran better after driving.

 

[RonD]

With IAC Valve unplugged idle should be 500rpms or engine may even stall, either is good it means IAC Valve is closing all the way, like it should.

There is an anti-dieseling screw on the throttle linkage, looks like an "idle screw" it isn't, if someone played with it then that would effect TPS and idle.

Check spring on throttle, and check throttle cable and cruise cable, either could be sticking.

 

[jeremysdad]

Why Ford Germany forgot to inform us that thermostats/water pump bypass valves were important? 'Not my problem.' Brats.

Hint: Water pump bypass hoses were important in the cologne motors (including the 3.0)...started with the 2.8 in the late model year Pintos...2.8...3.0 may not have been a 'cologne', but watch what a motor does if deprived of a water pump bypass. Blows headgaskets, is what. lol

SBC, SBF, BBC, BBF...all had bypass hoses. Didn't pop headgaskets.

 

[jeremysdad]

I...got off topic. Warranty whatever you can.

Vacuum leak.

Tearing mine down soon. lol

 

[jeremysdad]

****! 99? Bowing out! lol

 

[Rex2nr]

With IAC Valve unplugged idle should be 500rpms or engine may even stall, either is good it means IAC Valve is closing all the way, like it should.

There is an anti-dieseling screw on the throttle linkage, looks like an "idle screw" it isn't, if someone played with it then that would effect TPS and idle.

Check spring on throttle, and check throttle cable and cruise cable, either could be sticking.

The idle sounded like it dropped to 500-600, and didnt want to stall.

I havent touched the "idle screw" but maybe that needs some calibration.

I know the throttle itself moves freely, the gas pedal could be sticking though. No cruise control to worry about.

Why Ford Germany forgot to inform us that thermostats/water pump bypass valves were important? 'Not my problem.' Brats.

Hint: Water pump bypass hoses were important in the cologne motors (including the 3.0)...started with the 2.8 in the late model year Pintos...2.8...3.0 may not have been a 'cologne', but watch what a motor does if deprived of a water pump bypass. Blows headgaskets, is what. lol

SBC, SBF, BBC, BBF...all had bypass hoses. Didn't pop headgaskets.

I did headgaskets ~5000 miles ago. Its not running hot, oil and coolant are both clean.

Whats wrong with a 99? Lol

 

[Rex2nr]

I got it to idle today. I cleaned the MAF, tested the wiring to the IAT, and the sensor, tested the ECT and its wiring, cleaned the throttle body and adjusted the throttle stop screw, tested the TPS, and the IACV wiring. It idles at about 950 cold, but at least it's running. I had to move the truck out this morning to let my wife out (single car driveway) and stalled it three times.

I still need to check the ground RonD mentioned.

Thanks for the help

 

[enjr44]

Well adjusting the throttle stop screw just covers up another problem. The only reason it is there is to keep the valve from hitting and damaging the throttle body.

The IAC is the device that controls idle. The MAF tells the computer how much air is going into the engine and the computer adjusts the iac and injector pulse width for a desired rpm.

 

[Rex2nr]

I know it's a bandaid, but for now I can at least keep it running enough to get out of my driveway. I assume a new MAF is needed since it only idles at 5-600, 950 with the throttle stop adjustment.

 

[cp2295]

More likely an iac valve


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