I am not too familar with the mopar EFI systems and my girlfriends 98 SS/T has a issure when cold,the idle will get rough and can hear a high pitched vacumn sound coming out of the aircleaner but acts fine after the motor is warmed up. Is there a idle control motor that could be going bad and its not setting a code,I know on some of the Ford systems the IAC can go bad and not set a code like it did on my 89 crown vic but does it do the same on the mopars. Could it also be the coolant sensor too.

 

There is an iac & with age are known to hang up.
Located on the back side of the tb, held on by #25torx screws IIRC
Sometimes can get away with popping it out & spraying it with carb cleaner.
Dont push the plunger in.
Can test it by turning ignition to on/off(1 short of starting)
If it doesnt move in/out every single time or hangs up after spraying probably best to just replace it with the age of the truck.
TPS on the drivers side of the tb also known to cause idle issues & fail with age.

Does the tb has an open filter on it?

 

I presume all the sensors on the tb are original and it has over 150,000 miles and I guess it has what you can call a open filter,it has a chrome tube and one of those cone type filters.

 

i think they call those cold air intakes CAI. (should call them BWM big waste of money).

anyway the sucking sound is the air passing through the IAC which is moving in/out to try and keep it running. this might be more of a response to the poor running than the acutal problem, but the sucking sound is sort of normal. you can clean the port and pintle, maybe replace it for $40

vac leaks are common in the hoses around the engine bay, and all the way down to the 4wd t-case and cad. also the plenum on the V6/V8.

unless the idle is failing, i wouldn't replace IAC yet. if its moving in and out and keeping it running, then its doing its job. a bad IAC results in stalling or high idle.
check for vac leaks, look into a tune up, try to decide why its running rough when cold.

 

O2 sensor?

 

I know that type of aircleaner system is a little more noisier then what came on it from the factory but when the idle is starting to get rough the vacumn noise increases like something is trying to strangle the motor,both O2 sensors have been replaced along with the cat.

 

What brand o2's? And if the cat was replaced because it was clogged, do a search here for "plenum".

 

I think the O2s are Bosch and the cat was replaced due to it rattling and not plugged,what happens to the plenum when the cat plugs.

 

Got that backwards. The cat plugs when the plenum gasket blows, and you start sucking oil into the cylinders. (not to mention the unmetered air giving you some interesting running problems.) On a truck with 150,000 miles on it, it is a pretty safe bet that the gasket is indeed toast. (unless someone else fixed it right in the past.....)

Best way to check is the procedure outlined in the tech service bulletin, in the FAQ section here. Although, I have seen reports where the procedure gave a false negative. (plenum was blown, but, test didn't indicate that) Another method is to visually inspect it. Pull the throttle body off, and take a gander down into the manifold, if you see pooled oil...... time to yank it. Hughes and APS both make aluminum plates to replace the steel one that comes from the factory. Also, bear in mind, the intake bolts are torque to yield, and therefore NOT re-usable.

The general consensus that I have seen here is that the bosch sensors suck...... The dodge trucks seem to be a LOT more sensitive to aftermarket sensors, than any other vehicle I have worked on. I think the NGK? are the recommned O2 brand. For any of the other sensors, best to get them from the dealer.

 

It's NTK for the o2's! Other than that, use a light and a mirror to look around inside the intake, so you can see all 4 corners.