I have a 2000 F-150 with 214,000 miles that will get these codes only when it is below 40 degrees. The truck will run rough and the idle will surge between .6 and .9 rpm's. Usually after the truck warms up the truck will run fine. I have replaced the plugs and boots, cleaned the fuel injectors and replaced the fuel filter. The mechanic tells me the pvc boot behind the trottle body is fine (I think is correct). They are telling me to do this in order: re-program the computer, replace the MAS sensor and then replace the intake gaskets. I am tired of just throwing money at it. Any suggestions??

 

Read this:
http://www.obd-codes.com/p0300

Follow up on the solutions and recommendations. You'll probably find a vacuum leak. Make sure to check the PCV hose for cracks.

 

Thanks for your help. Several of the other postings also seem to go back to a vacuum leak (PCV hose).

 

I had the 171 & 174 codes last winter. It came down to replacing the entire PCV assembly from Ford ($28.00) and I tore down the MAF Sensor and cleaned the wires and diodes (i think they are diodes) really well with CRC electronics cleaner and let it air-dry. DO NOT touch the really fine wires in the MAF sensor, extremely fragile from what I have read.


The Ford PCV Assembly is complete from the PCV valve, followed by the plastic hard line tube, to the rubber elbow connector that connects to your throttle body.
Hope this works for you. Good Luck

TJKinCNY

 

Thank you for your input. I will try that next if what I had done yesterday does not work. I just had the computer re-programed and replaced the MAF sensor.

 

Re-flashing the computer and replacing the MAF sensor did not cure the problem. I have told my mechanic to replace the PCV assembly so I will see if this works.

 

Fuel presure
Brake Vaccumn booster line?

 

Well, I replaced the PCV assembly and the problem still has not gone completely away. It has gotten better but not completely cured. It ran rough enough the other morning to put the check engine light on when I started it. Yesterday when I started it up, the light has gone out so I will have to wait see what happens next.

 

No the code is stored. Go have it retrieved and tell us what it was. The actual code number not the garbage autozone or what ever tells you.

 

I had the codes read and they are the same PO171, PO174 and PO300-random misfire. I have not been able to correct the problem yet.

 

have you checked the fuel pressure yet? how old is the fuel filter? any exhaust leak?

this should help http://www.v8sho.com/SHO/TSB0197HO2SServiceTips.htm scroll down to p0171

 

I believe they checked the fuel rail on the passenger side and everything was fine. I replaced the fuel filter this past summer. As far as an exhaust leak, I don't think I have one. I did notice this morning when it was running rough as always while I warm it up in the morning, that you could hear a pause or a hiccup in the exhaust pipe. It is kinda hard to explain. I read and cleared the codes yesterday so when they pop up again, I will write down the fuel pressure readings and post it. What range should they read?

 

When was the last time you replaced your upstream O2 sensors?

 

Yea - It's probably the fuel pump. Can't give you any #'s until we know what engine we're working on here

 

check EGR and DPFE.