I have a 2003 RAM QC w/ the 4.7 and auto trans. A few months ago I first noticed a rough idle condition when sitting still at stoplight. The RPMs drop from their normal steady 600 RPM level down to around 500, maybe a little less. The truck has never died because of this condition, it just feels like it is idleing rough. The problem first happened early last fall when the temp was still above 70 here in Texas. I took it in to the dealership and got the standard, this isn't a problem...it's normal behavior explanation. It still didn't seem normal considering it hasn't done this before in the two years that I owned the truck. Once the weather turned cooler, the problem went away. Idle in gear at a dead stop is back to an even 600 RPM, smooth as can be. Now that it is springtime and warmer again, I've noticed that anytime the temp. outside is above 65 degrees, the idle in gear drops to a low 500 RPM level and feels rough. The old problem is back. If it's cooler than 65 degrees...it's smooth and steady at 600 RPMs. I just took it back in to the dealership again yesterday and got the same explanation that I did before. The thing that concerns me is that my truck will be out of warranty in about 6000 more miles. I realize that if the computer doesn't throw any codes, it is hard for the Dodge techs to know what to attack. I just don't believe that this is really a normal idle condition. Has anyone else experienced this and had it fixed? If so, what was done to fix it? I've come to accept the fact that if I want this fixed, I'm going to have to do it myself. Thanks for any words of wisdom.

 

I'd try a gas treatment first (STP) (cheapest solution $5.98). That should help you to see if its a fuel problem or a tune up is needed. Have you had a tune up? Sparkplugs, wires, coil and cap replaced (2nd option $180) but your truck should be giving you a code if you need a tune up? How many miles do you have on your Truck?

 

I tried the STP treatment last fall when the problem originally occurred...but it didn't change anything. My truck had 21,000 miles on it when the problem started...and now has 29,000 miles. I'll be performing a tune-up soon (plugs, wires, etc) in hopes that it will help but I kind of doubt it will. If the problem were related to a tune-up, the low idle should persist regardless of what the outside temperature might be. Right? There is a very distinct temperature line between good and bad idle conditions. When I leave for work in the morning's (temp is less than 65 deg), no problems and nice smooth idle. When I come home from work (temp is over 65 deg) the idle is rough and low RPM. I can't help but think the problem has to be related to something related to incoming air temp. I just don't know what to check, Mass Air meter, pressure sensor, etc ?

 

sounds like your IAT sensor it faulty.

all this does is monitor the temprature of the air comeing through the intake tube just after the MAF sensor.

if you pull it out you can test it with a reagular multi meter on the ohm range. as the temp goes up the ohm value goes down. you can take it and hold it near some ice and see what it does, then hold it near hot water. if the change in resistance is either very drastic or none at all the sensor is bad.

you should be able to find some values on the internet as to what the resistance will be at certian tempratures. if it is off it can cause this by makeing the engine run lean. now before you ask, the resistance comeing off this sensor also determins how the computer adjusts the values that are shown from the O2 sensors.

 

Thanks Drew, I'll run the test to see what's happening with the IAF.