Rough idle help

So to start I have a 2009 Dodge Ram 1500 with 260K miles. I had the cam go bad about two years ago and since then I have had a low rough idle only when I am at a red light. The engine will idle at 500 RPM's and sometimes lower. The engine feels like it is stumbling and vibrates like something is out of round. At cold starts, the idle goes to 12 to 1300 RPM's. In park, it runs fine.

The plugs are good, the PCV was just changed, the throttle body is clean, coil packs are good, fuel pump was just changed, injectors are good but it runs like crap at red light idle. Outside of that it runs great.

Anyone else experience this?

Try running the engine and spray either brake cleaner or carb cleaner around the intake manifold and throttle body. If the engine refs or drops/dies the. You have a vacuum leak at that spot. Check your coolant temperature sensor as well. The 1 for the engine, not the gauge. Any codes in your PCM that might help with the diagnosis? I’ve seen several sensors cause this but I’d rather do cheap diagnostics before recommending sensors on a truck I’ve never seen/touched.


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There are no codes. I'll run some brake cleaner tonight and see what happens. I'll report back in the morning.

You may have a bad ground. My last truck did that when i had a poor negative connection at the battery terminals.

So, there are no vacuum leaks. I sprayed a full can of brake cleaner on the intake, throttle body and all the vacuum lines and there was no fluctuation at all.

The only things that I can think of would be some dirt in the throttle position sensor, or possibly an idle air control motor or sensor although I don’t know which this engine comes with to be honest. You could try pulling the battery cables off overnight and see if resetting the PCM might fix it? A bad cam wouldn’t cause low idle and neither would a lifter. They would cause a rough idle though. Usually it’s a vacuum leak (which you checked) or the throttle plate position is off either due to carbon build up (which you’ve cleaned) or the sensor is reading it wrong and causing that. Not sure where else to tell you to look. Hopefully, 1 of the more senior guys pop in and offer some guidance or agree with my other suggestions.


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Big Daddy said:

So to start I have a 2009 Dodge Ram 1500 with 260K miles. I had the cam go bad about two years ago and since then I have had a low rough idle only when I am at a red light. The engine will idle at 500 RPM's and sometimes lower. The engine feels like it is stumbling and vibrates like something is out of round. At cold starts, the idle goes to 12 to 1300 RPM's. In park, it runs fine.

The plugs are good, the PCV was just changed, the throttle body is clean, coil packs are good, fuel pump was just changed, injectors are good but it runs like crap at red light idle. Outside of that it runs great.

Anyone else experience this?

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Ever get this figured out? I'm having an extremely similar issue myself. You described it perfectly that something feels out of round or stumbling at idle.

My 11 does this. 146k miles. Idle is rough till warm then it drops to 500 rpm and is smooth but at 500 rpm.

I can shift out of drive to neutral at a stoplight then back into drive and the idle goes up to 650 rpm

I've checked intake, changed plugs, pvc, done fuel system treatment, cleaned tb.

My truck has never had any work other than routine maintenance and exhaust manifold replacement. I run the 91 tune on I3.

I've quit looking. I could adjust the idle with my I3 but no need.

Bigskyroadglide said:

My 11 does this. 146k miles. Idle is rough till warm then it drops to 500 rpm and is smooth but at 500 rpm.

I can shift out of drive to neutral at a stoplight then back into drive and the idle goes up to 650 rpm

I've checked intake, changed plugs, pvc, done fuel system treatment, cleaned tb.

My truck has never had any work other than routine maintenance and exhaust manifold replacement. I run the 91 tune on I3.

I've quit looking. I could adjust the idle with my I3 but no need.

Click to expand...

bigsky looks like what has happen mine too so set tune up 50 rpm now instead 500 1200 so set on defrost and and it drops to 650 so ya be dang new exhaust new fuel injector plugs new never could find it ! ow new air horn dealer put in california emission up date and didn't ask me truck ran so crappy I 3 tuner fix a lot of problem s oh well last dodge I buy ! diablo doent have a idea guess ? me eather ?

Tighten your intake manifold bolts. Be careful, it's plastic, 8 to 10 ft lbs.

Solved the mystery