1998 Chevy Truck Rough idle OBD Code P0300

Tiny
SPLIFFY
  • MEMBER
  • 1998 CHEVROLET TRUCK
  • V8
  • 4WD
  • AUTOMATIC
  • 14,400 MILES
Hello, I have had this truck for 5 years with no problem. A friend borrowed truck to haul equipment 1000 miles away. When he brought it back, he said it will not idle and would barely stay running. (Nice friend). So here I am with a problem. I changed all plugs, wires and rotor. Flushed radiator, changed oil, oil filter, new power steering fluid, new brake fluid, and cleaned air filter. I pulled off intake and sprayed carb cleaner. I added marvel mystery to gas and filled tank up. With all that being done, it still has a rough idle around 400 on RPM gauge. Oil gauge fluctuates around 40. Headlights are dim, but when accelerator is pressed they go bright again. I definitely here a ticking under the hood. Fuel module in gas tank was replaced around 6000 miles ago. I also replaced the fuel filter about a month ago. Please help, I am confused. Could it be IAC, MAF or what?
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Wednesday, November 5th, 2008 AT 9:43 AM

4 Replies

Tiny
JDL
  • EXPERT
Is the ses like on, when your having the problem? Have the codes checked, some of the national brand autostores will check codes for free if you can get the vehicle down there. If there is a misfire code, it might tell you which cylinder/s is having the problem.

If you think the problem is a fuel issue, start by checking the fuel pressure. I don't care if everything is brand new, I'd still check fuel pressure.

As far as the fuel issue, if you have the csfi fuel system, there are bulletins about cleaning the fuel poppets. That is a shop procedure, I don't think pouring stuff in the tank will help
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Wednesday, November 5th, 2008 AT 12:49 PM
Tiny
SPLIFFY
  • MEMBER
This is the CSFI vehicle. The SES light does stay on all the time (3+ years now). I am a girl however I love to work on this thing. So should I go ahead and take the intake off and get started on the poppets? Would this make the truck have a missing sound almost like a tappet sound? The belt definitely needs to be changed.
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Wednesday, November 5th, 2008 AT 12:54 PM
Tiny
JDL
  • EXPERT
The po300 code can be awkward to track down, I sent you a private message, I don't know if you received it? Goodluck
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Thursday, November 6th, 2008 AT 9:03 AM
Tiny
RASMATAZ
  • MEMBER
1998 Chevy Truck Rough idle OBD Code P0300-Random Misfire normally results from vacuum leaks or bad fuel

Misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel
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Thursday, November 6th, 2008 AT 4:18 PM

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