Ok. I've got a cylinder 5 and cylinder 8 misfire, as well as an evap error code. P0300, P0305, P0308, P0455. The truck runs good when your driving but runs rough at an idle. rpms drop to around 700-800. Did the hughes plenum fix on it about a year ago and this is first problem I've had since then.

The Truck is a 2001 Ram 1500 4x4 5.9L stock intake, new wires, plugs, cap, and rotor around same time as plenum fix.

Any Help is appreciated!! I'm flat *** broke and hoping this is an inexpensive fix!! I don't have money to throw at my guesses lol

 

Evap codes are another issue, but if your plenum was blown and you didnt replace the pre cat o2 and the cat(or gut it) , I'm betting it's clogged. Unscrew the pre cat o2 from the pipe and see if it runs better.

 

Yeah I read up on all that stuff on here when I did the plenum fix, and replaced both front and rear O2 sensors but i'll try pulling the front sensor tomorrow and see. I've got the battery disconnected right now as I put a new IAC in it that was in my 99 ram that was just replaced last week. (thought that might be a cheap way to diagnose IAC possibility)

 

Pull the plugs on 5 and 8, see what they look like.

 

Yeah, was gonna do that tomorrow too. Can't work in the dark, (no garage) trying to get ideas tonight to try tomorrow and then come back here with updates Think it would hurt to run 1/2 - 1 bottle of Sea Foam through it? I've got 2 sitting in my storage building / shop. I'm willing to try anything thats free lol

 

when you did the plenum fix and was putting it back together did you make sure all the injector connectors were secure? check for leaks?

 

Ok, here's where I'm at - tried my IAC in it from my truck (it's only a week or two old) truck ran decent, little rough but nothing like it was and had no error codes. Tried using WD-40 around intake base checking for leaks - no noticeable change in rpms. Put original IAC back in, and threw P0505 code instantly. I had battery disconnected during each IAC change and turned on headlights to drain caps. Thinking I'm looking at bad IAC but going to pull plugs 5 and 8 now to check them for fouling. Anyone agree or disagree with this diagnoses? Like I said I'm broke as a joke and can't really afford to throw $35 at a misdiagnosed IAC, but I need my wife's truck back up and running so she'll leave mine alone lol

 

Did you try unscrewing the o2 sensor? Thats free, and a good test to see if the cat is bad.

 

Sure sounds like bad IAC.....

 

Checked #5 and #8 plugs have pic below. found a little fuel on #8 but nothing major, checked spark on both cylinders with spark tester and have spark jumping 0.50" gap (plugs set at 0.40") so I've got good spark. Pulled Front O2 sensor, no change aside from noise level which was expected. only thing that has changed since doing IAC change is truck is now idling around 1,000 to 1,100 rpms, which is where it's always ran at since we bought it, but still idles rough.