95 ram 2500 5.9l 4x4 it will idle up and down constantly. it idles down to the point where it will almost stall then rev up and then back down any ideas?

 

it also bogs after about half throttle and will backfire when letting off the gas

 

When does it do it? All the time? Immediately upon startup? After running for a couple minutes?

 

happens all the time. to me i think that the idle and the bogging/backfire is 2 different problems

 

Check for vacuum leaks, test the TPS, see what you find.

 

Sounds like the Idle Air Control motor to me - except for the backfiring part. Check for vacuum leaks first, and also exhaust leaks. These can cause the backfiring. I think you have two separate issues - the IAC for the bad idle and something else causing the backfire....

 

doubt its an exhaust leak. does anyone have a diagram of how the vaccume lines that are going to the intake and throttle body are supposed to be i removed them a little bit ago maybe messed it up?? how do you test iac and tps? voltmeter? what should they read?

 

Check tps with an analog meter. (the kind with a needle that sweeps across a scale) Ground the black lead, put the red lead into the cavity for the signal wire to the PCM. (center wire). have your scale on 5 volts, if available or 10, if it isn't..... at closed throttle, should be right around one volt, increasing STEADILY to right around 3.5 volts at WOT. if the needle bounces around as you open the throttle, replace the TPS.

IAC motor either works, or it doesn't. You can clean the throttle body, and end of the IAC motor, but, that's about it.

Should be a vacuum diagram sticker somewhere under the hood.... (emissions label?) If you can find it, it's also in the factory service manual. (you can them from the faq section here.)

 

I went back to my notes (I used to really frequent the forum a few years ago) and found a question like yours that I answered with:
The RPM fluctuation problem is either a dirty or bad Idle Air Control motor on the back of the Throttle Body. You can probably fix it by removing the throttle body, removing the sensors, and cleaning it real good with carb cleaner. the IAC has a plunger that goes in the hole in the back of the tb. The plunger and the hole are probably gunked up. The TPS (throttle position sensor) is on the drivers side of the tb. It goes bad a lot also - but the common problem when it goes bad is a "rpm jump" at cruise speed, not at idle. the IAC is where you need to focus with your issue.
I would try cleaning it first. It fixed mine...

 

ok it turened out to be leaking intake manifold gasket