I have a '94 Ram 1500 with a 5.9L and lately while idling I can hear what sounds like a vacuum leak or sucking air. I start it and it idles fine for about 30-40 seconds and then it idles lower like it might die and I can hear that sucking sound. I popped the hose off the pcv valve while it was doing this and it idled right up. The sucking sound seems to be coming from the back of the motor somewhere, but I cant pinpoint it. I have Recently replaced: plenum and gasket, pcv valve, IAC, egr valve assy.( due to the last one was melted at the plastic). Any ideas what to look into? Thank you.

 

that almost sounds like a pluged converter

 

Usually, a VAC leak will induce a higher idle as your allowing MORE air into the intake. This is how the TB works, OPENING the throttle plates increases the air flow which raises the RPMs.


What it sounds like you've got going on is a blown IAC motor driver CKT or, the PCM wasn't reset or, the IAC passages at the PCM level are totally obstructed with carbon build up in which case, you would need to remove it and clean it 100% with Acetone or suitable solvent along with replacing the gasket as well.


That sucking sound usually emanates from the rear of the TB at the IAC valve most likely. I think it's starving for air thus the low idle condition.


Check your air filter as well. A clogged air filter will also choke off the air supply but, only in running mode. Closed T-plates and low idle condition is usually a result of a stuck pintle valve at the IAC.


Start there.


CM