Looking for some ideas. Just picked up a Ranger for my kid. When I brought it home it had the P171 and P174 codes. It was leaking oil from the valve covers. So, I replaced the lower intake gasket, injector o-rings and plate gasket, upper intake seals, valve cover gaskets, EGR valve, plugs, wires, air filter, EGR o-ring in upper intake, EGR valve pressure sensor, PCV valve and the PCV hose, and sprayed out the MAF sensor. Upon initial startup, there were no codes and ran very strong. After warming up and taking a short test ride, the P171 and P174 codes returned and the engine idle is sometimes rough...at times sounds like it is ready to stall and then returns to a smooth idle. I have checked and do not notice any vacuum lines broken or collapsed. Any thoughts would be helpful.

 

What kind of wires did you use? My first tune up i used the advanced store brand and it did not seem to like them at all. I picked up a set of motor craft wires and all is well. Also what type of plugs? I have never had any luck with any other than motorcraft in mine that may be a starting point.

 

sounds like a vacuum leak to me. I know on the 01+ trucks, there is a vac line that always cracks right underneath the Throttle body that cause the same codes. Maybe the older trucks have it as well? worth a shot

 

Wires and plugs (SP500) are motorcraft OEM. All main vac lines are plastic and there are none broken/melted. PCV hose replaced. Power brake booster vac hose is good. There is one large vac line at the throttle body that runs over to the drivers fender. I initially thought about it but it did not look or feel bad. Will recheck that line. Thanks!

 

Any additional ideas... I have replaced the:
Spark Plugs,
Plug Wires,
All intake and valve cover gaskets,
Injector o-rings,
EGR valve,
EGR o-ring in upper intake,
EGR valve pressure sensor,
PCV valve,
PCV vac hose,
Large vac hose at throttle body to fender sensor,
All remaining large vac lines,
Air Filter,
and sprayed out the MAF sensor.

Under further insepction I found that he EGR delivery tube was cracked. It has been replaced with a new one. Intially started the motor and no code. After driving approximately five miles, codes P0171 and P0174 are back. I have rechecked the plastic vacuum lines and none are broken or loose. The only part that I can see as a possible issue left is the MAF Sensor. Any other ideas would be helpful. Thanks!

 

Fuel pressure should be checked. Acceptable range is 56-72psi at idle and under load.

 

All of you suffering p171 lean bank codes and mystifying vac leaks. Check the hose to your rear antilock on the left side of the engine - feel along the bottom, mine was visually OK but rotted out - and the one going to the brake booster. And....pull the element from the MAF with a #10 star drive and replace the o-ring. These are hard won searches. That paid off for me.