Hey everyone,
I have a 2001 Dodge Ram 1500 4x4 with a 318 (5.2) and a 5 speed. The mods have have done is a flowmaster 40 series, 285/70-17 tires, and 2" wheel adapters to go from 5 bolt to 8 bolt.

The problem that I am having is that when I start the truck after it has been sitting over night or after school it will start right up but it has a rough idle and sounds almost like it is cammed for about 30 seconds to 1 minute then the rpms will come up and back down as if you tapped the gas and the idle will smoothen out and get progressively choppy again. The idle will go up and down again like before one more time them run perfectly fine.

I already replaced the plenum and intake gaskets, spark plugs, wires, cap and rotor. These made no difference. I also tested the throttle position sensor, it is working as it should, I tested the MAP sensor, it is working, and I checked the IAC sensor and that is moving as it should (I think). Lastly I checked all the vacuum lines and all of them hold vacuum as they should.

I bought the truck with this problem from a mechanic and he said he could not figure out what is making it do this but he said he was not worried about it. He owned the truck since it has 90,000 miles on it (it has 184,000 now).

I posted about this problem a few months back but did not really get anywhere so I figured I would post it again after I did the intake gaskets.

I am honestly stumped as to what it could be. Thank you guys for any information or comments you might have. Sorry for such a long description.

Thanks again,
Frank

 

Did the iac have a lot of carbon build up? Clean it and the throttle body and see if it changes. It may be time for a new iac. Also what condition is the battery in?

 

I would definitely try a new, mopar IAC. Clean the throttle body, new TB gasket. What about the IAT too?

 

Okay, thinking about it, you probably already used a new TB gasket (I hope). So, pretty much, the engine has to be cool again before it will repeat the issue. I presume no codes. Does it sound like it is misfiring? Sound like maybe an exhaust leak (cracked manifold)? I am thinking that something is wonky until the engine warms up a bit. But probably not the O2 sensor, may be worth a try though???

Here is something to try. Going with the premise that once something warms a bit, it starts working normally, go to a PC store (fry's) and get some of what I call freeze spray. It's a spray refrigerant used to cool components in a computer (to troubleshoot them, see what is flaky when it gets too hot). If you cannot find any freeze spray, you can use canned air (used for blowing out PC dust bunnies). Use the can of air upside down, it will get pretty cold too. Spray the freeze spray on assorted sensors, distributor, PCM, maybe even spark plugs, crank sensor if you can get to it, etc. Maybe this will cool things enough to help nail down the problem.

Added a pic, for your viewing pleasure...

 

The throttle body and IAC were cleaned when the intake gaskets and plenum gasket were replaced and all new gaskets were put in. There does not seem to be any exhaust leaks and it is not throwing any code which is why I am so lost with this. If it through a code I could maybe have a direction to go in haha. Thank you for the tip and I will try that one day this week after work and let you guys know what I come up with.