the dreaded rough idle... - Ranger-Forums - The Ultimate Ford Ranger Resource


4.0L OHV & SOHC V6 Tech General discussion of 4.0L OHV and SOHC V6 Ford Ranger engines.

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  #1  
Old 01-02-2006
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the dreaded rough idle...

sometimes (very, very randomly) when i start it it will idle REALLY rough, like a diesel then die.. to cure it i have to hold my foot slightly on the gas to keep it running....

not sure if this is related but it seams like everytime i start it it wil idle rough for like 1/4 of a sec then overcome it on its own...

anyhow i have made some observation the first 2 times it happened.. the first 2 times i had a tank full of low grade BP gas, and i thought thats what did it... but just tonight i was proven wrong... i have UDF (mobile 1) gas in it now...

anyhow what do you guys think the problem is... at first i though maybe the battery is week... because for the first few seconds before the PCM and altenator engage the truck runs off of the battery... but this happens so speraticaly that i doubt this is the problem...

anyhow here is some info...

2002 4.0 4x4 auto XLT, syn. oil 5w30.. 35000 miles
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Old 01-02-2006
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Same thing here

2.3 1997 93000 miles 2x4 auto
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Old 01-02-2006
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Mine does the same thing sometimes!
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Old 01-02-2006
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okay on some model this will work..if you look on the throttle cable where you can pull the lever to accelerate it, there sould be a screw. Use a flat head to lower or raise it...I did it too mine and its alot smoother. Hop it helps :)
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Old 01-03-2006
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ill have to give that a try... is that like an idle ajustment screw? if so will it screw up the way the truck runs when it is running right?

and that doesnt sound like a fix for the problem... id really like to know why the heck its doing it... and why its SOO random... i am thinking maybe there is a little water in the fuel system... ill have to get an additive to remove it... and if fue filters are cheep i might get one of thoes too.... and i think i am going to go buy a locking gas cap...
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Old 01-03-2006
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Quote:
Originally Posted by RedRanger02
ill have to give that a try... is that like an idle ajustment screw? if so will it screw up the way the truck runs when it is running right?
It's more of a travel stop for the butterfly in the throttle body. Since the idle speed is determined by the EECM, any change to the throttle body will be compensated for by the engine computer. Depending on how large of an adjustment you make, the time for the computer to adapt may be transparent.

For example, I have to adjust my throttle body every winter because the throttle body sticks closed (thanks to the expert service from my local dealer), and it usually doesn't change the engine RPMs at all. The first time I made an adjustment, I had to turn the screw down far enough that the engine did idle fast, but the EECM "learned" the new air flow, and lowered idle speed accordingly.

I hate to throw parts at a problem without knowing the actual cause, but here's a suggestion. I had always heard that when you have a rough idle problem, especially one that is intermittent, the problem may lie in the spark plug wires. I know you only have 35,000 miles, but if you can't find any other possible causes, it might be worth a try.

Keep us posted on how it turns out.


EDIT: You say the rough idle only lasts for 1/4 second after starting. Mine does the same thing too, but lasts for a couple of seconds. It's only on a cold start, when the ambient temperature is below about 50 degrees Fahrenheit. It idles rough, and hangs at 1000 RPM for a couple of seconds. It smooths out and climbs to the 1500 RPM cold idle and everything is fine. It's done this from day one. After four years, I've learned to live with it. The dealer can't fix it, and the powertrain engineers on Ford's service hotline say that although it's not normal, it's not a problem.

I've read other threads where guys have suggested changing or cleaing the the MAF sensor, replacing the air intake temperature sensor, coolant temperature sensor, idle air control, or throttle position sensor. I wouldn't go that far, but if you can check the voltage output from each sensor on a cold start and compare that to the tolerances allowed by Ford, you might get somewhere.

My bottom line is that I have read a lot about the problem as described in my EDIT, but have yet to find a definitive solution. Good luck.

Last edited by mkoenig; 01-03-2006 at 07:55 AM. Reason: additional info
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Old 01-03-2006
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unhook your truck from the battery (negative wire only)negative battery cable back up and this will reset the pcm.(truck turned off)

after 10 min or so, hook the negative battery cable back up and start the truck. let it idle for a while 5-6 min with the havac off and all accessories off.

once that 5-6 min is up turn on the defroster and let it run for 5-6 min.

the above helps reset the pcm's learning curve.

now if that doesnt fix it you might want to look into cleaning or replacing the IAC (idle air controller) search around on RF for info on the IAC.
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Old 01-03-2006
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thanks for the info zach.... i gave it a shoot, and whille i was waiting for the 10mins, i checked all the plug wires, cleaned the MAF and IAC.. and i am now at my parents in Akron (about 150miles from my house) so since i knoew i was going to be going through a tank of gas today i bought some good fuel system cleaner..

so far it seems great.. starts right up doesnt evan stumble for that first 1/4 of a sec...
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Old 01-03-2006
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Are you getting any spark nock when driving like putting stress on the motor up hills and at like 65 or 70 MPH?
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  #10  
Old 01-04-2006
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I wouldnt think the IAC is bad unless its having idle problems at other times.
as well as a loud "moaning" noise.

You might try this. Turn the key to run.. let it sit for 2-3 sec THEN start.
I've found mine starts alot easier this way.


Rand
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Old 01-05-2006
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I'm glad to hear you've got it running better. From what you described it almost sounds like a rich condition, often times a dirty sensor can cause this. You may also have a slightly fouled O2 sensor, not off enough to trigger the CEL but enough to throw the mixture off some. Varnish in the fuel system can cause things like the FPR sticking, or an injector leaking or sticking. I'd say if it's better now, things just needed a little scrubbing, if it resurfaces you may try checking sensor outputs as suggested, and possibly try recallibrating your TPS and resetting again. Just a couple thoughts...
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Old 01-05-2006
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that happened with my truck and what i did was use throttle body cleaner and it was amazing at the gunk that came out when i did it and i do it every month or so. also i find that when it is cold to turn the key to run and let the fuel pump kick on then it runs good.
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Old 01-05-2006
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try running some seafoam or injector cleaner perhaps?
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Old 01-05-2006
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Iac Iac Iac!
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  #15  
Old 01-05-2006
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actually i am hopping to get a programmer from Doug so i ams ure that will help alittle too....
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Old 4 Weeks Ago
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Quote:
Originally Posted by The Black Ranger View Post
Are you getting any spark nock when driving like putting stress on the motor up hills and at like 65 or 70 MPH?
my 93 ranger with 3.0 has started this knock now it either idles fast or dies,sounds like it's getting too much fuel .any idea what the problem may be?
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