I have a 2000 ram 5.2, runs rough at idle and in gear, is ok when driving down the road, have replaced cap,rotor,plugs,wires, intake gaskets, and it still feels and sounds like it is missing, with no check engine lite. I am stumped What would cause this? Would the IAC make it run like that? And before I forget the pve valve is rattling at idle, checked and no vac. leaks. I dont want to throw parts at it. Also checked the cat, its fine. And the fuel preasure is 45 psi

 

PCV valve (I'm assuming thats what you meant at the end of your post) is less than $10 at a dealership. I'd definitely get that replaced, cheap and may need to be done anyway depending on your mileage.

IAC could do this, as well as pre-cat O2 sensor. Did you read this entire thread? It covers all of that.

 

replaced iac and tps, no change in the way it runs, thx buy the way I will try the o2 sensor

 

Replaced the o2 sensor and no change in the way it runs

 

Did you reset the computer (PCM) when you changed the various parts?

 

when the last time you did tune up. pull plugs pull # 8 and see if its fouled , check cat see if thats clogged also.

 

That's the poor man's engine management setup to where, you shut off some cylinders when you don't need them. Saves on fuel! Then, when you need power, you pop the hood and rewire for all eight!

CM

 

Yes, I reset computer, cat is ok. Might just take it to the dealer, almost about to give up, have been working on this thing for a week now and have spent alot of money. Just dont understand why it runs rough at idle and in gear, then clears out when driving or when pushing on gas pedal. Noticed a slight hesitation while in park while reving it up. But changed all the parts and still no change. and still no check engine lite. hooked scanner to it and no codes, and no memory codes

 

Vacuum leak?

 

Looks like there's multiple posters in this one thread here. I missed your problem and thought you were the one who'd found the wires to be crossed over. Such is not the case after re-reading this through this morning here.

THere's quite a few items that are not monitored by the control system. That's the fuel delivery system and the IAC / AIR-flow for starters which, it will run rough.

Since I know this system inside and out as far as operation, function, and control systems perspective, I know what happens during both, idle and running conditions.

Let me explain it out in detail for you as to what I think may be occurring in your case.

At idle conditions; the THROTTLE PLATES are closed thus, the only air controlling device is the IAC motor. The A/F ratio is dependent upon this valve to open and close to a specified amount.

How it works is this: The PCM sets a PRE-SET value for this in degrees of motor steps at time of installing the motor. Upon initial install, the stepper motor valve assy is in a compressed state thus, the pintle valve assy is not protruding nor extended into the bore.

It is assumed that NO POWER is applied to the PCM memory at this stage and, all previous data stored in memory at the PCM level is totally cleared out of old sensor data.

The negative battery terminal is reconnected and, the PCM goes through it's initiating reset process. It now awaits <KEY ON> EVENT.

When <KEY ON> EVENT is initiated, the PCM applies voltage to IAC motor and, it performs what is called- TOUCH DOWN SEQUENCE. The pintle valve is slowly driven until it touches down into the seat of the bore at the rear of the throttle body. This is extremely important here for, this measured distance in terms of motor control steps is what the PCM uses from here on out to determine WHERE, the pintle valve assy is in relation to the seat of the bore. This point is now used to calculate the HOME POSITION of the pintle valve assy.

From here on out, it knows HOME POSITION by counting the motor steps thus, the air gap can precisely be set. If for any reason, the PCM LOSES COUNT, or, there's an anomaly in the controller to where the data has been corrupted in memory, or a mechanical anomaly such as debris, jamming, binding, mis-alignment of the pintle valve assy or whatever, the PCM has NO WAY of knowing where this valve is and it's called LOST REFERENCE / or LOSS OF HOME position.

So, at start up- the PCM positions the IAC to achieve proper A/F ratio at startup.

When you open the TP at the Throttle Body, the PCM now closes that IAC valve and, all air is now flowing through the throttle body and, the A/F ratio is adjusted by means of the O2 sensors once the PCM has switched over to closed loop mode. In warm up mode, the O2 sensors are not looped into the controller. Once the timer has counted down 2-3 minutes and, the engine temp limit that is programmed into the PCM program has been met, the PCM will only then switch over to closed loop mode and, it factors in the O2 sensors to help control the A/F ratio.

This is most likely the reason why the engine feels fine when running and not so when in idle and under loading / in gear.

HOW TO FIX / ACTION ITEMS:

Remove the Negative BAT terminal off the bat.

REMOVE the air hat assy / AIR intake assy.

REMOVE all sensor connectors at the throttle body level. IAC, MAP and TPS

REMOVE the THROTTLE CABLE

REMOVE THE TV cable from the rear of the throttle mount bracket.

REMOVE VAC line

REMOVE four bolts that secure the TB to intake manifold.

REMOVE throttle body from intake.

NOTE condition of TB. If black and loaded with CARBON BUILD UP- it will need to be cleaned 100%.

HOW: use ACETONE or any suitable solvent. CAUTION: Do not use ACID based products on Al.

PRIOR TO CLEANING: remove all sensors and set aside.

REMOVE any traces of gasket material and clean it until it looks brand new. Clean the entire thing top to bottom using toothbrushes until it's shiny and new looking.

Get a new gasket by FEL-PRO

Get some Gasgacinch

CLEAN intake gasket interface area using Acetone

ClEAN TB gasket area

APPLY gasgacinch to TB and let dry 10 minutes.

APPLY gasket to TB and roll out bubbles using clean socket.

TRIM gasket to exact opening size using Exacto knife. Discard any loose pieces of gasket material and ensure NO loose fragments of gasket material are on TB.

REPLACE THE IAC with OEM only. I've gone through three out of the box from 3rd party vendors that didn't work properly. Do yourself a favor and go with OEM on all sensors.

INSTALL all sensors into TB.

FASTEN TB onto intake and align gasket to intake openings best you can. Finger tighten bolts to prevent moving around during torque sequence.

Torque TB fasteners to OEM spec. I think torque spec is 19-inch lbs if my memory serves me correct.

There's other possible root causes for what you describe but, this is the MOST COMMON failure mode associated and, judging by the fact that, when it is running OR, you press on the gas pedal- it runs fine, that is a very good indicator that the problem is rooted and isolated at the IAC / TB level.

PS: Fuel pressure reading is at at the low end range by the way. SPEC SAYS: 49 psi ± 5. Also, measure it while running and under load conditions for accuracy.

CM