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-   -   Surging Idle/Throttle-Help! (

cshe091 10-05-2012 09:58 AM

Surging Idle/Throttle-Help!
My problem is that intermittently my truck has a surging idle. It does not do it all the time, but I will get an idle that fluctuates between 400 rpm, and 1000 rpm. So far it has not stalled. Sometimes it will also rev up to around 2500 rpm as I'm coming to a stop, and push in the clutch. After it goes to 2500 it always comes down to around 650. I have replaced the TPS, Map Sensor, Idle Air Control, cleaned the throttle body, changed the spark plugs, and reset the APPS sensor. I'm not getting any trouble codes, and it runs great except at idle. I get no hesitation whatsoever going down the highway. I have had it at the dealership, and they can't get it to recreate the problem so that they can investigate. It does it probably 2 out of every 5 times it is driven. I'm getting really frustrated at this point. Does anyone have any suggestions?

snrusnak 10-05-2012 11:16 AM

Man that's tough without an engine light...

Maybe a vacuum leak, fuel pressure regulator issue...?

cshe091 10-05-2012 11:32 AM

I checked for a vacuum leak using carburetor cleaner. I would think that a fuel pump or fuel pressure issue would be seen across the whole range from idle to full throttle. It is super frustrating.

RamTech 10-05-2012 11:42 AM

Did the dealership check the PCM flash level to see if any updates are available?

cshe091 10-05-2012 11:44 AM

I am not sure if they checked the PCM flash level. What would that do?

RamTech 10-05-2012 12:16 PM

A newer version may address a problem like the one you have.

cshe091 10-05-2012 12:24 PM

I just got off the phone with the dealership. They said that the firmware was already updated to the latest version when they got it. They have looked at all of the electrical outputs of the sensor, and say that they fall within range. Unfortunately they haven't been able to get the truck to idle erratically while the computer has been hooked up. They did say that the have escalated it to a star case? They are hoping to have more information within 24 hours.

snrusnak 10-05-2012 12:47 PM

EGR, IAC. I know you said you replaced the IAC, but was it an oem part? I've replaced sensors with aftermarket poor quality parts and caused running issues in the past... Also what's an APPS sensor?

RamTech 10-05-2012 12:59 PM

APPS stands for Acceleration Pedal Position Sensor. It's used on vehicles with ETC.

snrusnak 10-05-2012 01:02 PM

^oh ok. 2004 4.7L didn't have ETC correct?

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