1999 Silv 1500 (P300) Sputtering

[cammedup]

All,

I have been fighting my truck for a while now. It is throwing a P300 random misfire. It sputters badly during intown driving never dies but idles very rough. I can be sitting at a red light with the truck sputtering and vibrating and suddenly it will just come out of it and run fine. Seems like something just clicks and vroom it runs normal. Or if I jam the pedal to the floor and it will rev up and seem to run fine at high rpm. I have changed one O2 sensor, EGR and all plugs and wires. Here is the funny thing, when the oil has been changed it doesn't seem to act up as much. When the oil is old it does it every time I drive it.

Should I change the rest of the O2 sensors? Are the CATs clogged up? What could this be?

[intel_guy]

Mine does that only when I drive in the rain. Thought I had it fixed - found a loose ground wire in the firewall, but the symptom came back...no luck yet.

[ukrkoz]

please, save money by spending time on pinpointing the cause.
try this:

http://www.2carpros.com/first_things..._run_rough.htm

[j cAT]

Originally Posted by cammedup

All,

I have been fighting my truck for a while now. It is throwing a P300 random misfire. It sputters badly during intown driving never dies but idles very rough. I can be sitting at a red light with the truck sputtering and vibrating and suddenly it will just come out of it and run fine. Seems like something just clicks and vroom it runs normal. Or if I jam the pedal to the floor and it will rev up and seem to run fine at high rpm. I have changed one O2 sensor, EGR and all plugs and wires. Here is the funny thing, when the oil has been changed it doesn't seem to act up as much. When the oil is old it does it every time I drive it.

Should I change the rest of the O2 sensors? Are the CATs clogged up? What could this be?

If the O2 sensors are over 100,ooomi replace them ,, this is all they are designed to last you may get 20,ooomi more out of them but you risk damaging the cat's....and you will loose on MPG's replace upsteam sensors...minimum..

rough idle can be many things I would look at the PCV and if not changed replace and also carefully inspect vacuum lines for cracks and softness[collapse]....

as was mentioned loose and corroded grounds can cause many problems so all grounds need to be checked for security...

this includes the fuel pump ground connection at the frame rail next to the fuel tank....and if all this goes nowhere fuel presssure ,, and the cleaning of the throttle body/IAC, and while all that is removed use CRC MAF cleaner and clean the small maf sensor wires..


If the engine runs good at high rpm's its probably not the plugs or plug wires..

[timbob_45]

hey i think your truck probably need a fuel pump tape a hooked up fuel pressure gauge to you windshield and watch the pressure while you drive around. It should be around 55-60 psi