Idle goes down to 500 when stopped in Drive

[jmd4100]

My 2007 Ram 1500 5.7 Hemi-when warm- at a stop light will decrease in rpm to about 500 or a little lower almost as though it is being strained by the tranny because when I put it in neutral it climbs right back up and when put back in drive it stays up. Only after I accelerate does it happen again... and when I put my foot on the brake and give it a little gas the problem also stops... thinking 02 sensor or torque converter... anyone?

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[Fast69Mopar]

Is the check engine light on? Has it been on and off recently? Just because the check engine light is not on doesn't mean the PCM has not stored a 1-trip failure. If it has it could be a big clue to help in diagnosis.

If this is a torque converter issue, check to see if the Converter Clutch is operating normally.

When driving and coming to a complete stop, let the engine idle settle to the lowest rpm point. Once it's reached the lowest rpm, move the shifter to Neutral. Does the engine RPM flare higher than normal, say 1000-1500rpm?

Perform a test drive. Press the TOW/HAUL button so the tow/haul lamp illuminates in the instrument cluster. Start driving in a location so you can accelerate normally above 40mph. Under normal, light throttle application the torque converter clutch will apply in 3rd gear and the engine rpm will drop about 200-300 rpm.

See if it is operating like it should. This will help aid in your diagnostics.

 

[jmd4100]

There is no check engine light. It's never been on. Like you said, it could be the PCM. Transmission is otherwise working as it should. Its just at a complete stop I watch as the engine has 650-700 rpm just slowly but surely drop to 500 or so and oil pressure drops slightly-as expected from low rpm

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[jmd4100]

There is no check engine light. It's never been on. Like you said, it could be the PCM. Transmission is otherwise working as it should. Its just at a complete stop I watch as the engine has 650-700 rpm just slowly but surely drop to 500 or so and oil pressure drops slightly-as expected from low rpm

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[jmd4100]

Oh and if ac is on the problem does not happen

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[SYKRAMMAN]

Oh and if ac is on the problem does not happen

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My truck does the same thing. I was told that it takes some time for the voltage regulator to catch up but I find that difficult to believe, I know the regulator is in the pcm but there has to be an answer for our problem. Mine has been doing it for over a year, no cel’s or anything else abnormal. Maybe that’s just the way it is, idk. I’ve had other vehicles do the same.

 

[Fast69Mopar]

There is no check engine light. It's never been on. Like you said, it could be the PCM. Transmission is otherwise working as it should. Its just at a complete stop I watch as the engine has 650-700 rpm just slowly but surely drop to 500 or so and oil pressure drops slightly-as expected from low rpm

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The oil pressure gauge will go lower when the idle rpm has fallen that low.

When this thing is idling in gear with the brakes applied, does it sound like the transmission is straining?

What does the fluid look like?

Smell like?

 

[jmd4100]

The oil pressure gauge will go lower when the idle rpm has fallen that low.

When this thing is idling in gear with the brakes applied, does it sound like the transmission is straining?

What does the fluid look like?

Smell like?

I'm not totally sure how a straining tranny would sound but you can hear a slight whirring getting lower in pitch as rpm drops and I just changed both filters and fluid 2k miles ago in my backyard. I used the genuine Mopar fluid and Wix filters so I'm sure it's nothing to do with those, and the problem occurred before and after the fluid change.

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[Fast69Mopar]

I'm not totally sure how a straining tranny would sound but you can hear a slight whirring getting lower in pitch as rpm drops and I just changed both filters and fluid 2k miles ago in my backyard. I used the genuine Mopar fluid and Wix filters so I'm sure it's nothing to do with those, and the problem occurred before and after the fluid change.

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How does the truck run overall? Still have good performance?

Is the fuel economy consistent?

My 2004 and 2005 5.7 HEMI's idle pretty low. Most of the time they idle about 575rpm on the stock tune.

 

[jmd4100]

How does the truck run overall? Still have good performance?

Is the fuel economy consistent?

My 2004 and 2005 5.7 HEMI's idle pretty low. Most of the time they idle about 575rpm on the stock tune.

Yes the truck runs great overall. I'm getting about 11-12 mpg city and 20-24 highway- due to MDS. 575-675 is about what I like to see but 450-500 is a little to low. If it idled in park and neutral at 500 I'd say it's ok. But when it only idles that low in drive when the engine and transmission are warm that makes me believe it's too low of an idle

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[Fast69Mopar]

Yes the truck runs great overall. I'm getting about 11-12 mpg city and 20-24 highway- due to MDS. 575-675 is about what I like to see but 450-500 is a little to low. If it idled in park and neutral at 500 I'd say it's ok. But when it only idles that low in drive when the engine and transmission are warm that makes me believe it's too low of an idle

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After thinking about this issue, I went back and looked through some customer complaints to see if I could find some that were relevant. What I have done in the past was cleaned the throttle body.

Remove the 4 screws from the throttle body and disconnect the electrical connector.

Clean the throttle body with brake cleaner and a towel and maybe a toothbrush if you have some build-up.

Most of the trucks I have seen with the low idle like this has really dirty throttle bodies with heavy carbon build-up around the throttle blade.

What does the inside of the throttle body look like?

 

[jmd4100]

I'll check it. Thanks! I have classes today till 2 so I'll check it when I get back home. Thanks for the tip. I'll let you know

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[Fast69Mopar]

I'll check it. Thanks! I have classes today till 2 so I'll check it when I get back home. Thanks for the tip. I'll let you know

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If you can, take some pics of the throttle body so others can see what it looks like before and after cleaning.

Hope this does the trick for you. Let me know what happens!

 

[jmd4100]

If you can, take some pics of the throttle body so others can see what it looks like before and after cleaning.

Hope this does the trick for you. Let me know what happens!

Well here's it dirty, and here is also the intake. I think that's rust but I'm not sure. The clean is also there. And even after all that, the problem still occurs

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[jmd4100]

The before and after of rpm from in drive. And drive-neutral-drive

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[Fast69Mopar]

Here is what I would do next.

I would shut the truck down and disconnect both battery cables and touch them together. Doing this will discharge the system. Reconnect after 10 minutes and retest.

 

[jmd4100]

Here is what I would do next.

I would shut the truck down and disconnect both battery cables and touch them together. Doing this will discharge the system. Reconnect after 10 minutes and retest.

I did that first...

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[hotrod45]

It's normal for the idle to drop from whatever it is in neutral to a lower rpm when it's put into drive. It does seem odd that when you stop in traffic, the rpm drops slowly. Here's what I see as the most important part of your description: if you put it in neutral, the rpm comes back up . . . and the "problem" doesn't reappear until you have operated the throttle. To me, it sounds like a throttle position sensor issue.

 

[jmd4100]

Yeah @Fast69Mopar gave me some advice with that. I cleaned it with carb cleaner and wiped it down and reinstalled. As shown in the pictures, it had some crud on it but it wasn't terrible. Cleaning it did do something because it shifts at a lower rpm now. It doesn't hold it out for an unnecessarily long time. I'm thinking the tranny is somehow straining it. The tps is at 16-17% at idle according to my scan tool which is what I like to see. I've had problems with the truck before but this one really stumps me... thinking about buying a new one but once I install it I can't return it... it's about $130 by me at Autozone

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[jmd4100]

Here is a video of exactly what happens. Watch as I shift into neutral and rpm goes up and back in drive it stays up

https://s.amsu.ng/huowtwcFwHFN



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