Mechanics

I HAVE A ROUGH IDLE

2001 Ford Ranger • 74,000 miles

I have a 2001 ranger and I have a rough idle I replaced the iac maf sensor pcv valve and cleaned the throttle body but still no change It runs good while driving just at idle it stumbles not to the point where it stalls just poor idle any advice would really help thanks
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Derek97116
September 18, 2011.




You could have a vacuum leak. Sometimes a bad O2 sensor will cause a rough idle as it gives the incrrect air/fuel value to the computer causing a rough idle.
Also, the throttle position sensor could play some part, but not as likely.

Vacuum leaks, compression test, check plugs and ignition system, scan for any unresolved faults, not all faults will set a light, check EGR operation, start here.

Mhpautos
Sep 18, 2011.
I did hook it up to a scan tool there Is no miss fires and no codes poped up and I did change the throttle position sensor as well I think its a vacum leak but wouldent that show up on the scan tool and do you think plugs and wires would solve the issue even when its not miss fireing and the o2 sensor where is that located and what does that do to make it not idle right

Tiny
Derek97116
Sep 18, 2011.
You can test the plug wires for resistance by the foot. I do not have specifications for that though. I will try to find them becasue that is possible.

The O2 sensor will be in the exhaust path before the catalytic converter. If it thinks the engine is running lean it will put too much gas in the mixture and it will run rough. Same goes for it thinking it is rich, but this is harder to detect and will possibly damage top end parts.

With the o2 sensor wouldent it spit a code if that was bad and the only time the check engine light has come on was for the egr valve and I took it to a mechanic and he said the egr was fine but he changed the maf sensor since that I haven't had the light come back on and I have a buddy with the scan tool and no codes at all show up so idk

Tiny
Derek97116
Sep 19, 2011.
It can be failing and not throw a code. That is one of the things that is frustrating about electrical diagnosis. Parts fail slowly or intermitantly and until the senor fails or goes out of its' specified range, (performance can still be affected when part is within specified range), it is hard to track down the failing part.
The mileage you have is not really where I would ussually see one fail, usually closer to 100,000, but it all depends on the wear and tear and maintenance on vehicle. Of course. Things just happen as well.
I think the next step would be to either run some high quality fuel system cleaner, such as SEA FOAM or BG44K, and see what that does. Run a can or 2, which you might have to go to a service station to get, and be prepared to change the oil afterwards as they are so good at removing deposits it tends to dirty the oil up when used.
The other things I have in mind. If I have not mentioned already, are fuel pressure and possibly a failing fuel injector. You might check the fuel pressure manually witha gauge at a test port which should be on the fuel rail.
Try that and the fuel system cleaner first. If that does not work, it is getting near time where the O2 sensor should be replaced, by the way if you have seen a change in MPG that is a indication that it is going bad, as it is nearing the mileage I would suggest it be replaced. It never hurts eithr as MPG will be optimized as well as air/fuel ratio.
See what that does then get back to us.

I have ran a couple bottle of fuel injector cleaner and It hasent changed a thing where is the o2 sensor and if that is going bad would that make engine stumble at idle and I have noticed my truck does not get that good gas but I figured since it has a lift and its 4wd that may have a say in it and is the o2 sensor easy to change thanks drcrankwrench for your help

Tiny
Derek97116
Sep 19, 2011.
Failing O2 sensors will as a rule sent the ECU into a rich mode, this will often account for poor economy and may also be the cause of the stumble, with that said, have you done a fuel rail pressure test as this can indicate a leaking injector that will also give the same problem as well, wort considering doing the test.
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Mhpautos
Sep 19, 2011.
As far a fuel system cleaners go, you would not believe the difference in SEA FOAM and especially BG44K. BG can go for $20+ a can, but nothing else comes close to working like it does.
You will need to get some WD40 or PB Blaster to saok the sensor to ease its removal. You can find it in the exhaust path after the manifold but before the catalytic converter.
You will also need a special sovet to remove it if you connot get to it or have room to turn a wrench on it. It will have an electrical connector on it that you will have to trace up to the connector which will probalbly be as far in as the engine compartment.
I would really give the BG or SEA FOAM a chance, but plan on changing the O2 sensor anyway. Other Items that may be dirty and affect performance are the Idle Air Control Valve, which handles changes in engine load, and the Fast Idle Thermo Valve, which acts like a choke. You can try 2 cans of Bg which works so well at removing deposits, you will need to change the engine oil after using it from all the gunk it removes.
You may have to remove the throttle body and clean it and the aforementioned parts as well.
Having the lift kit will drastically change MPG, so don't consider that.
Let me know if you need anything else.

Where is the Fast Idle Thermo Valve, I have all ready replaced the iac valve cause when engine is cold and it idles at like 900 to a grand it sounds fine once it gets warm and drops to 600 or whatever it starts doing that

Tiny
Derek97116
Sep 19, 2011.

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