New guy here but I'm a long time reader. Here is the whole deal. I have had my 2002 5.9 1500 4wd for years with no problems. In 2009 I received orders overseas for 2 years, so my truck went in storage. I got back in the states in April and flew to Dallas to get my truck this is when my problems started. On my drive to AR.(Where I'm from) it drove good for the first half of the trip. It felt good to be reunited, but on my last leg running about 75ish and she started to buck. I just thought it was bad gas. At my parents house and began to troubleshoot. Bad gas was out of the question, I had ran through that initial tank. I didn't have much time to dick around with it because we had a 9 month old little girl that had never seen her grandparents. So I sea foamed it and still nothing. after that we headed to IL. to see my in laws and it was the same song second verse. Through all of this I was glued to this site trying to pinpoint my problem. Finally I had to report in TX. for training. After all the miles of crappy mpgs and trying not to blow my motor I actually have time to work on it. The first job I did was the Plenum Kit. I finished this afternoon and the bang thing still runs like crap and to add to the mess, the truck now idles at 1100 rpms or so. (900 with ac on) I don't think this is normal. So to sum it up. I have the symptoms of a blown plenum gasket, bad spark knock at hwy speeds, decelerates on inclines, bad mpgs and no power. I don't have smoke or oil consumption. The old gasket had no blowouts and looked good FML. oh if it matters my PCM has the update sticker on it. Anyone's help would be greatly appreciated! oh no codes eather.

 

I would suspect O2 sensor(s) first..

 

Remove the front O2 sensor from the exhaust, take the truck for a drive. See if it's any better. Yeah, it'll be a bit louder....

 

Thanks for the replys yall, I haven't tried the O2 test yet. I forgot to mention that the cat is removed and replaced with pipe. I remember reading a thread about the o2 sensors would read bad if you didn't use spacers of some sort? I may be wrong.

 

The rear o2 can set a cel sometimes after removing the cat. If you don't have a cel on now then you're fine. Don't need a spacer for the front o2. Don't get a Bosch o2 sensor - go with denso or ntk. They're a lot cheaper on rockauto or Amazon.

 

Check all your plugs, wires and stuff like that.

And use copper plugs, makes a world of difference.

The O2 sensors should only throw a code, shouldn't actually effect anything else

 

So where are you stationed?

+1 on checking O2 sensors. Getting a CEL? How long (or hoe many miles) since plugs have been changed? Pull the plugs and take a look at them. Also got to FAQ/DIY sdection and look for the TSB on plug wire routing. Does it seem to be missing?

 

Make sure all plugs are tight to plugs and cap and follow tsb .

Maybe clean your Iac on back of throttle body

 

Pull/replace the dizy cap & rotor, after being parked for two years it might be corroded green.

 

And keep in mind that if your plenum was blown before then a coupke of those spark plugs may be fouled out from the excessive oil.