My truck starting idling really low last week and then the engine light came on, It was the po300 code, checked the plugs and one bank was really rich and the other bank was fine, put new plugs in and swapped O2s from side to side to see if it was the O2, sure enough the other side was rich, put a new O2 in and took it for a ride and it breaks up really really bad but the plugs look fine.
So I decide to change the plug wires cause they are the originals and have 94000km on them and thought maybe I had a bad wire, changed the wires and it still breaks up really bad at idle and under load.
If I rev it up in park, at about 3500 and up the speedo will start going up aswell.
Does anyone have any clue of what could be the problem???
Thanks Mitch.

 

well about the speedometer mine comes up as well when i rev it thats normal the adnormal idle is wierd where does it idle at?

 

A code P0300 may mean that one or more of the following has happened:

* Faulty spark plugs or wires
* Faulty coil (pack)
* Faulty oxygen sensor(s)
* Faulty fuel injector(s)
* Burned exhaust valve
* Faulty catalytic converter(s)
* Stuck/blocked EGR valve / passages
* Faulty camshaft position sensor
* Defective computer

Why do I get the feeling its None of the Above.

 

Since you changed the o2. Clear the code and see if the same one comes back.
just a thought.

 

Its cold out here so normally on a cold start it will idle about 1800 but now it idles at about 1000. When its warm it normally idles about 550-600 but right now it goes under 500 and idles rough.

 

I had the code cleared when I did the plugs and the light has not come back on.
When the engine was warm I took some snow and dropped it on every cylinder on my headers to see if I had a dead cylinder and the snow melted off every cylinder so I dont have a dead cylinder but could have a weak one due to not enough spark.
This is driving me crazy, lol

 

have you tried cleaning your throttle body. if not then disconnect your battery while you are doing this to clear the memory on the pcm. when you fire it back up it should re-learn idle.

 

+1 for cleaning the throttle body...

 

I will try that but what about it missing really really bad under load?
Thanks for the help guys, I would be out there wrenching on it to try and find out whats wrong but its really cold out and my truck doesnt fit in anyones garage thats close to me, I have to drive a good 20 minutes to get to a garage that I fit in. lol
I try what I can till I get to cold. haha

 

That's why they suggested cleaning the TB. Clean the MAF sensor too.