Had a question. This doesn't happen all the time but when its warmed up and i come to a stop light it will idle rough and have a very loud hissing sound until i punch the gas it goes away. I did a tune up and replaced the iac. I checked for vacuum leak via carb cleaner and had no idle change. Any ideas on this? Sounds like it coming from around iac area. I tested the new iac via ohm meeter and was within spec. Thanks a lot

I did do new

plugs,wires,cap,plenum gasket and plate, iac.

 

Hissing is vacuum. Check crank case vents. One hose on each valve cover.

 

2nd that

 

It would most likely hiss all the time, but is the round gasket installed between the TB and air cleaner? And what brand IAC did you use, and was the negative battery disconnected when you replaced it?

 

ok i will double check for leak. Yes there is a gasket where air cleaner and throttle body meet. Not sure of the brand off the top of my head but it was what advance auto gave me. no i did not disconnect battery.

 

Did you get the filter housing seated completely with the lip around the TB, sometimes I think I do, but not quite.

 

Yeah i double check that. What bugs is that i can go half a day and then it starts. Could be like 1 or 2 times that's it. Last time it did that it was doing it i tried to open hood to try and hear what area its coming from and truck died. and no codes of course.

 

Do you or a friend have a scanner like a SnapOn MT2500 or newer/equivalent. Go in and reset the adaptives, IAC, fuel etc. Sometimes just disconnecting the battery doesnt cut it. There is a keep alive in the ECM for such things as battery changes etc.

 

No scanner like that. Happened this morning still sounds like its coming from iac area. Really loud when i took off air cleaner. I can hear a high pitch whistle iac area. Checked ohms again got .46 was told it should be .50 and under.

 

im havin the same problem with my 99 2500 it got a lil better when i changed the pre cat o2 sensor with a mopar one (ntk) it does it every now an then but mainly when idling for more than 5 minutes in gear it doesnt do it in "p" or "n"... it was really bad before i put in the offrad y pipe