2000 F150, 5.4L 4x4

First things first - I blew a heater inlet hose and thoroughly drenched the engine in coolant. I pinched off the line and limped it home. It took me a couple of days for the repair as none of the normal tools would get the quick connect fitting to release. I ended up using a small screwdriver to break the fitting and tear it apart.

I pieced it back together with the required 5/8" to 3/4" reducer (16mm x 19mm... whatever!) and off-the-shelf hose. Not clean, but perfectly functional.

I drove about 35 miles, and pulled up to a stoplight. It almost died when it went into low-idle. It bumped itself back to high-idle and seemed okay. I pulled away from the stoplight and everything seemed just fine. Driving a couple times since and it's the same thing - doesn't like low-idle. The CHECK ENGINE light came on and I figured oh good that will certainly help! So here's the plethora codes....

P0131 - O2 sensor circuit low voltage (bank 1, sensor1)
P0134 - O2 sensor circuit no activity detected ( bank 1, sensor 1)
P0171 - Fuel trim malfunction (bank 1)
P0174 - Fuel trim malfunction (bank 2)
P1131 - lack of H02S11 - sensor indicates lean
P1151 - lack of H02S21 - sensor indicates lean

My first thought is the Idle Air Control valve (IAC) is lijely stuck open. I've noticed when letting off the gas it doesn't slow down like normal and still wants to pull itself along as if stuck in high-idle (again not seeming to like low-idle). I think it's a problem with the IAC, but probably an electrical one to throw that many codes? I think I'll remove and clean it as I've had to in the past. It's been a couple years at least and it's probably due anyway. Probably spray down the electrical connection with some contact cleaner. I'll clear the codes and see if the driveability improves.

Thanks for any advice!

 

Sounds like a large intake vacuum leak. I'd leave the IAC alone for the moment.

Check that PCV hose carefully all the way to the 90 degree elbow on the back. Have to check by feel left-handed. That elbow is a high failure rate part.

 

Found it! LOL! I had already disconnected the IAC valve and was getting ready to unbolt it and saw this....



I cleared the codes and have driven about 70 miles since - all good! So many codes from that little hose!

 

Good find and follow-up.

I'd suspect that hose got knocked loose while working on the heater hoses.

 

Yeah, I'm sure that was it! I spent way too much tjme trying to get that hose off. Thanks for the tips SHO89!