I have a 2001 Ram 1500 5.9l gas. It idles really rough, it runs fine going down the road, when you come up to a stop the rpms will drop to 300-400, then pick it back up to 600 and then will die. It will start right back up again. The rough idle happens cold and operating temperature. There is no check engine light on. Fuel pressure is good, injectors are firing, compression is good, but only pulling 13-14 inches of vacuum. Can't find any vacuum leaks anywhere. This is on a new remanufactured motor, have replaced the following:
Distributor
Drive gear
Iac valve
Map sensor
Throttle position sensor
Intake gasket
Belly pan gasket
Throttle body gasket
Plugs
Wires
Cap
Rotor
Belt
Hoses
Radiator
The plenum and throttle body came off my old engine which was running just had a knock. Don't understand what could be causing this problem. Any help would be greatly appreciated. Thanks.

 

the low vacuum concerns me. is it a stock engine or does it have a cam in it?
has it had this problem since day 1?
have you checked the compression?
after replacing the distributor, have you check the fuel sync setting?

 

Has a high torque towing cam. It has done this since I first started it. Compression is between 130-150 on all cylinders. How do you check fuel sync setting?

 

You need a snap on style scanner to set the sync unless you are pretty damn good and give it a go by hand like I did using the indicator marks in reference to the distributor from an old motor I blew up a while ago...

I got mine to be +1 or -2 degrees from 0 degrees center by doing that mostly by taking my time, listening to the motor, and knowing the general area the dizzy was supposed to be aligned with.

As sad as it is to say though, I don't believe that your problems are coming from there.

Try getting a butane torch. Open its valve all the way while your engine is running, and let the gas from the torch be your guide. If you have vaccum leaks, the gas from the torch will be pulled into the motor, mixed with fuel, and thus burned which will smoothen out your idle issues. Where ever you find an area that when you bring the torch into you find yourself smoothing your idle, you will have identified a potential vaccum leak. If you dont find any smoothing effect, then vaccum leaks are not likely your issue.

Facemask would be an excellent tool as well, just in case of a splash of inferno to your face.


Any codes or check engine light?

 

No codes and check engine light is not on

 

Those are classic symptoms of an IAC stepper motor problem, though I suppose it could be something else. I would get a scanner that can read live data, and look at the IAC counts. Scannerdanner did some recent videos of this on youtube.