I have a 2001 5.2l ram that runs fine until heated up then it starts surging and pulsating like I'm pushing and letting off gas. I'm neutral I can hold the pedal down to 2000 rpms and hold it then it'll rev down to about 1500 then back to 2000 and keep doing it until I let off gas .. it'll idle fine .. new cap,plugs, wires, tps, coil, plenum and fuel pump I don't know what it could be. Any help would be greatly appreciated.

 

How old is the O2 sensor?
How old is the PCV valve?
Got any vacuum leaks?
Can you redline it with a quick hit of the go pedal?

 

O2 and pcv I've never changed. So unsure. No vacuum leaks I can hear or aware of. And yes if i hit pedal quickly it'll go to redline

 

Disconnect the front O2 sensor, and see if it runs better once it warms up.

 

Already tried that. Someone said it could be the iac or coolant temp sensor. Would either of those do that? I'm just making sure before I load the parts cannon..

 

I was just reading the 2001 service manual and it is saying that the MAP sensor is the number one contributor to fuel injector pulse width (how long the injectors are open/how much gas they spray). There are a few videos on YouTube showing how to test it. A failing sensor can cause surging.

IAC is only supposed to operate when the throttle plates are closed. If it was malfunctioning then you would have surging (or too high/low) idle any time you let off the go pedal. You could pull, clean and check the operation. With the IAC out and laying where you can see it, turn the key on and make sure the pintle goes in and out smoothly. It has a little screw connected to a little motor so don't push/pull on the pintle when it's out. It's easier to check if you have a helper to turn the ignition on/off so you can hold the IAC in your hand.

 

If you turn the ignition on with the IAC just laying there, it will launch the pintle, and you will never see it again..... (don't ask how I know this..... )

 

I've done it a couple times on my truck and it didn't do that, it moved out/in/out then stopped somewhere in the middle of its range of movement. The PCM has a set point that it moves the pintle to when you start the truck and it's in open loop.

 

The one I tested was an aftermarket unit..... and as soon as I turned the ignition on, it ran itself all the way out, and then the spring shot it across the garage.... Never have found it......

 

So maybe cup your hand over it when the ignition turns on, just in case.