when car idles the rpms pulse like someone is pumping the gas


Asked by Jan 05, 2014 at 05:46 PM about the 2003 Ford Explorer XLT Sport V6

Question type: Maintenance & Repair

I have a 2003 Explorer sport and recently when the car idles the rpms pulse like someone is pumping the gas. the rpms only jump up about 500 and its seems like its getting worse. It pulses about twice a second. any ideas on how to fix it? After a bit it will stall out, ands doesn’t do it till engine warms up then, I can’t even stop at a long light and it will pulse and stall. Tried a new MAF $300 still same. Check engine ilghton, tested, they said 80% chance it was the MAF,

18 Answers


Sounds like either a dirty/faulty idle air control valve or dirty throttle body.

3 out of 3 people think this is helpful.

The IAC going out. Idle Air Control valve. These are also known for intake leaks. Using propane or brake cleaner won't find the leak because it is usually the lower intake that can't be picked up by spraying.

4 out of 4 people think this is helpful.

I did remove and clean out the Idle air control Valve. as best I could, it didn't seem to make any different. I was just hoping that cleaning it would get better than I would know for sure before spending more.

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Turn your a/c on. Truck should idle up. With a/c off turn steering wheel all the way to the left. It should idle up. If your truck does not idle up in these cases I would replace the idle air control valve.

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Usually cleaning doesn't work on Fords and I would recommend motorcraft not aftermarket.

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bad throttle position sensor.your throttle goes up and down when they go bad it will get worse and start to stall.

7 out of 7 people think this is helpful.

Good point Colin. I over looked that.

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to dandyoun,thats what the forum is for, sometimes with different views we get to solve the problem.

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I would agree with Colin except for one thing. TPS will set a check engine light on a ford and an IAC won't.




turns out it was an intake manifold leak witch was letting two cylinders run a lean code when vehicle warmed up, then sending wrong info to MAF which was sending wrong fuel info . etc.

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Glad you found it. I get it right occasionally.

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rpm are not working on my 98 ford explorer. sometimes they work but other times the don't. What can be the problem

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Same problem here . went to Damions Auto Shop In Sterling Heights MI & was told I needed a new battery & idle motor. the final cost $ 517.61

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So it sounds like I might have the same prob. Either the air control valve or the throttle position sensor. How would I know the difference and what price should I be looking at? Had one mechanic look at my sport and give me a 'low est' of $2500-3000. Wouldn't tell me what was wrong tho. Read this thread then looked up the parts, less than $400 both. Is this normal or should I get a diff mech?

Edit: is there any way I could do either myself? Yes, I have tools and have worked on old cars. 1960ish era tho.


this is copied from another poster also know that there were recalls on certain models of explorers due to faulty TPS...mine is a 95 Hi there, after spend several months doing research on How to fix my High Idle condition on my Explorer 1998, after doing a lot a repairs, replaced parts, it seems to me I found the problem.... I did all service required to fix any vacuum leak, new IAC, cleaning all connectors, new intake gaskets, no errors codes, no nothing just the engine sometimes gets the idle increased between 800 to 1500 RPM then I did this... 1º Using a needle, measured sensed voltage at TPS while engine Idle and Hot. I found 1.092 Vdc 2º When the engine start increasing idle took readings again and found 1.116 Vdc !!! but the throttle plate was in its stop pin, so why the voltage is now higher??? Reading some old ford manuals (4.9L, feddback carby, 1986) I found the TPS voltage should be around 0.850 to 0.900 Vdc while idle. The old PCM ignore any voltage between 0.900 to 1.000 Vdc because the internal voltage reference regulator can supply voltages between 4.950 to 5.050Vdc depending on the PCM temperature. It explain why sometimes the TPS and all other sensor can return minor voltage differences even registering the same engine condition, then I guessing... Probably the PCM Internal Voltage reference regulator on my explorer was producing the voltage variation but the TPS voltage still been so high so I did... 3º Using pliers I did turn the Throttle Stop Pin back while measuring voltage at TPS signal wire and found the voltage was reduced from 1.116 to 1.060 Vdc and the Idle immediately return to normal 650 RPM !!! 4º After doing some more test and experimentation I found the PCM ignores any TPS voltage under 1.100 and the minimum TPS voltage I could obtain was 0.960Vdc after using several different TPS sensors. It makes me think: when the PCM receives voltages over 1.100 Vdc "Think" the driver is light pressing gas pedal then it respond increasing Idle by commanding IAC to do so...!!! 5º I found also the TPS screws let a minor TPS sensor rotation also, just a few degrees but enough to increase the TPS voltage over the ignored limit of 1.100Vdc. Problem Fixed, just adjust the TPS sensor to the lower possible voltage and if still not been enough, move slightly the Throttle Stop until the TPS voltage is reduce under 1.100 Vdc. WARNING: Be sure the throttle plate still making stop over the Stop pin, not in the internal wall of the Throttle body or wall damage/wear will appear.

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