High Engine Idle

camoman214 · Jan 11, 2012

1999 Ram, 5.9L, auto, 4x4

I just replaced the IAC valve on my truck 'cause it wouldn't idle and figured the IAC was bad as per OBD scan. Now the truck idles at 1800 rpm and I can't get it to idle down to normal. I did the proper IAC adjustment which calls for driving at 40 mph to allow ECM to learn the setting, but that didn't work.

Rogan68 · Jan 11, 2012

verify your TPS setting is correct.

Also, ensure your throttle cable isn't hanging on something, or improperly adjusted.

camoman214 · Jan 11, 2012

What should the proper setting?

Rogan68 · Jan 11, 2012

I just checked, and the TPS on the 5.9 is not slotted, therefore, not adjustable. Sorry for the confusion..
If you have, or know someone with a good scanner, they should be able to connect it to the OBD port, and see if the TPS voltage is within spec at idle (I believe it's around .9VDC)

Another thing to check is vacuum lines; ensure you have no leaks anywhere. A vacuum leak can cause a high-idle issue, as well.

camoman214 · Jan 11, 2012

Awesome, thanks. I have a scan tool at home, so I will get a voltage reading tonight.

For reference, approximately what is the (IAT) temperature supposed to be at idle after the truck is warmed up?

Rogan68 · Jan 11, 2012

The IAT reading will depend on how hot the intake air is.. I don't have a resistance/voltage scale on the IAT handy. I'd say temp-wise, at operating temperature, +40*F over ambient.

camoman214 · Jan 13, 2012

Hey Rogan68, thanks a lot for the reply. TPS was it.

Rogan68 · Jan 13, 2012

Awesome! Happy motoring!

camoman214 · Jan 13, 2012

Well I guess I spoke too soon. After replacing the TPS sensor and driving the truck last night, the truck ran fine and idled normal. Today, I started it up and now it's idling high again, just as it was before.

Rogan68 · Jan 13, 2012

Try reseating the tis connector

per Tapatalk on my EVO

camoman214 · Jan 13, 2012

Rogan68 · Jan 14, 2012

Sorry, autocorrect struck.. TPS not tis.

per Tapatalk on my EVO

camoman214 · Jan 16, 2012

Reset unsuccessful.

Mopar1973Man · Jan 16, 2012

camoman214 said:
Today I unhooked the battery again for 12 hours to reset the ECM, but still idles high. You said to reseat the TPS.. do you mean just remove it and reinstall or is there a procedure for reseating?

Any other thoughts?

I wish that myth would go away... Unhooking the batteries doesn't reset any computer or erase error codes. Everything is permanently programmed on PROM chips and the code will never be change or altered unless you happen to have a DRBIII tool from dealer.

Disconnecting Batteries and crossing cables - YouTube

The only thing that is lost is throttle calibration.

camoman214 · Jan 16, 2012

Mopar1973Man said:
I wish that myth would go away... Unhooking the batteries doesn't reset any computer or erase error codes. Everything is permanently programmed on PROM chips and the code will never be change or altered unless you happen to have a DRBIII tool from dealer.

Disconnecting Batteries and crossing cables - YouTube

The only thing that is lost is throttle calibration.

Oh, I did not know that. I always thought it would reset and lose the stored info. Do you have any ideas of what I should try next?

Mopar1973Man · Jan 16, 2012

This isn't 100% but the ECT coolant sensor will alter the idle on the Cummins diesel for warm up I assume the same should be true on the V8 gasser series so if the coolant temp is too cold it will idle high and if the coolant temp is too hot it will idle low. This can be verified with a live data tool like a Scangauge II.

As for other thing I would look at vacuum leaks, IAC in the throttle plate, etc... Because technically the throttle plate are closed completely and the fuel/air ratio is controlled by the MAP sensor and O2 sensor to keep a clean idle by giving air or giving fuel so if there is too much air leaking in (vacuum leak) to keep the mixture correct it will add fuel hence a high idle will occur.

As for the battery disconnect... Just think of the PCM like a thumb drive on your laptop... You write information to the thumb drive then remove it and place it in your pocket (battery disconnected) then some time later (even years later) plug it back in and the information is still there just the way you left it. The PCM follows this exactly. The only way to reboot the PCM is turn the key OFF and wait a few minutes and start the truck again the PCM is force to do a reboot and used store programming in PROM (Programable Read Only Memory) which requires a Dodge DRBIII tool to even alter, change or flash entire PCM.

Now I know older vehicle like my 96 dodge has the ability of dropping the error codes with disconnecting the batteries. But this is not fully true either because you might of wiped out the error codes but a flash code 12 remain alerting a tech that you cheated and pulled the battery to hide error codes. So even that is not a fool proof way of erasing...

camoman214 · Jan 27, 2012

Mopar1973Man said:
This isn't 100% but the ECT coolant sensor will alter the idle on the Cummins diesel for warm up I assume the same should be true on the V8 gasser series so if the coolant temp is too cold it will idle high and if the coolant temp is too hot it will idle low. This can be verified with a live data tool like a Scangauge II.

As for other thing I would look at vacuum leaks, IAC in the throttle plate, etc... Because technically the throttle plate are closed completely and the fuel/air ratio is controlled by the MAP sensor and O2 sensor to keep a clean idle by giving air or giving fuel so if there is too much air leaking in (vacuum leak) to keep the mixture correct it will add fuel hence a high idle will occur.

As for the battery disconnect... Just think of the PCM like a thumb drive on your laptop... You write information to the thumb drive then remove it and place it in your pocket (battery disconnected) then some time later (even years later) plug it back in and the information is still there just the way you left it. The PCM follows this exactly. The only way to reboot the PCM is turn the key OFF and wait a few minutes and start the truck again the PCM is force to do a reboot and used store programming in PROM (Programable Read Only Memory) which requires a Dodge DRBIII tool to even alter, change or flash entire PCM.

Now I know older vehicle like my 96 dodge has the ability of dropping the error codes with disconnecting the batteries. But this is not fully true either because you might of wiped out the error codes but a flash code 12 remain alerting a tech that you cheated and pulled the battery to hide error codes. So even that is not a fool proof way of erasing...

This is some great info.

Sorry for my slow reply. I really appreciate everyone's help on this forum. Thanks.

Rogan68 · Jan 27, 2012

I've used spray carb cleaner to find vacuum leaks in the past

camoman214 · Mar 19, 2012

Thanks for all the replies. Turns out there was a frayed wire leading from the IAC to the PCM that caused my high engine idle.

Robert · Jun 18, 2013

try reseting the pcm this worked for my 07 4.7

High Engine Idle

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