nunnzie

Newbie here and have been using this site to help fix recent problem on my F150. I have a 02 F150 4.2 L with 95K miles. A few months back I had a misfire problem and also had check engine light codes P0171 & P0174. Based on what I read on this site concerning these codes I have replaced the coil, replaced the MAF and pulled the plenum and replaced the bolts with the green gaskets and replaced the big o-ring for the plenum cover. My misfire problem is gone but since then my truck has developed a rough idle (only when AC is off) and also it does something really strange when I go in reverse. When I put it in reverse the rpm's go up and down 500 to 1000 - up and down where it really starts jerking the vehicle. It will smooth out if I stick it in N or D. I went back to Azone last night and pulled the codes again and in addition to PO171 and 0174 it now shows 2 new codes P1151 and P1131. Reading this site for those codes seems to indicate bad O2 sensors. I also checked all of the vacuum hoses for leaks but don't see anything obvious. My concern is I seem to be doing too much trial and error with just buying parts and seeing if it fixes the problem. Seems like the only problem I fixed is the misfire. I am ok with buying the O2 sensors but would like to have a good feel that is the problem before I keep throwing money at the problem. Anyone have any advice that could help?

st8ic

Reset the computer and see if anything changes. Very strange problem indeed. My first reaction was vacuum leak.

2000xl_toronto

Sounds like a vacuum leak for sure to me. Is it possible that the plenum is not seated or torqued down properly and there is a vacuum leak from the plenum itself?

nunnzie

I will once again search all of the vacuum tubes to see if there is a leak somewhere. I am pretty sure when I re-installed the plenum that everything went on well and properly torqued. One thing I heard on this site is you can spray carb cleaner around the perimeter of the plenum and if the engine revs up it is a sure sign that the plenum has a bad seal. So I will try that also.

cbh3d

I just had the same problem. The misfires and the high idle, I got the same codes as well, P1071 and P1074. It ended up being a crack in the PCV pipe.
Replaced it, and she runs fine.

gghopks

Check the vaccum hoses and tubes from the pcv valve to the intake.

These elbows and plastic vacuum pipes go bad with heat etc. after a while and cause all kinds of problems.

You can buy the replacement set for the pcv vacuum hoses and pipes from Ford about 40-50 bucks and put it on.

nunnzie

I pulled every hose pcv hose off this weekend and checked each individual hose for leaks and checked all elbows and they all passed the inspection. I also took carb cleaner and sprayed it around the plenum and the engine never responded which shows that has a good seal.

So I guess my next move is to go ahead and purchase new O2 sensors and replace them unless anyone else has anthing they can think of?