MY 98 EXPEDITION BEGAN TO IDLE ROUGH.CHECKED THE COMPUTER CODES AND GOT P0171 (SYSTEM ADAPTIVE FUEL TOO LEAN BANK 1) AND P0174 (SYSTEM ADAPTIVE FUEL TOO LEAN BANK 2).ANY ONE HAD THIS PROBLEM.ANY HELP.THANKS.

 

Haven't had the problem on my vehicle, but the manual lists the 174 code common causes are, fuel pressure, air intake system, crankcase vetilation, engine vacuum, HEGO (injector harness).

171 common causes are, poor connection at HO2S'S, faulty MAF sensor, faulty CID sensor, small vacuum leak(s), CNAP leak(s).

I would start with the air intake system, clean / no leaks after MAF and electrical connections secure.
Next the HEGO system, HEGO not carboned up, connections secure.
Then try for vacuum leaks, loose hose(s) concentrating on the canister purge system.

Good luck, hope I was of some help, if not it looks like your off to your local FORD man. Let me know how you make out.



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Jim H

 

JIM THANK YOU FOR THE INFORMATION I WILL TRY THOSE STEPS YOU POSTED. MY EXPEDITION HAS 46,000 MILES. I HAVE NEVER HAD ANY ENGINE PROBLEMS. I CHANGE THE OIL EVERY 3000 MILES. I USE PREMIUM 93 OCTANE FUEL.WHEN IT STARTS IT RUNS OK WHILE THE COMPUTER IS IN OPEN LOOP MODE TILL IT WARMS UP THEN ONCE IT WARMS UP IT STARTS TO IDLE ROUGH. WHEN I DISCONNECT THE BATTERY I CLEAR THE CODES AND IT RUNS OK BUT AGAIN ONCE IT HEATS UP THE CHECK ENGINE LIGHT COMES ON AND THE CODES RETURN SO DOES THE ROUGH IDLE. I HAVE READ ABOUT 02 SENSORS GOING BAD BUT I AM NOT GETTING ANY 02 SENSOR CODES. THANKS AGAIN FOR THE INFO I WILL POST MY RESULTS. MIGUEL P.

 

Those are lean codes, you are running lean on both banks so most likely your hego sensors are ok, they most likely didnt both fail at the same time. Have you changed the fuel filter yet??? You may have a vacuum leak whick would make sense with a rough idle. You also may have a faulty MAF sensor. Built into the MAF sensor is a BARO sensor. The Baro measures your altitude and adjusts you fuel accordingly. You have to change the MAF if there isa BARO [barometric pressure] problem. THe rough idle concerns me the most telling me there is a simpler problem here....IF both sides read lean it is probably a vacuum leak, check all the lines. Other causes can be an injector problem [poor injector[s] or injector driver[s] in the PCM], fuel pump or pressure problem, eletrical misfire.....etc... How is the power under load??? does it "ping"????? either way it is lean or it thinks its rich and is compensating with a lean mixture. Good luck....
Dave

 

 

Look at the pcv hose, behind the throttle body, you probobaly have a vaccum leak there, the fix is easy, either get a piece of hose to replace it or go to the dealer and buy a new pcv tube.

 

GWH YOU ARE 100% RIGHT!!!! I JUST CHECKED THE PCV HOSE AND IT HAS A RUBBER PIECE AT THE END OF THE HOSE BEHIND THE THROTTLE BODY THAT HAD MELTED AND CRACKED.I COVERED IT WITH MY FINGER AND THE TRUCK RETURNS TO NORMAL IDLE. THAT WAS MY VACCUM LEAK. I WILL REPLACE THE PCV HOSE RIGHT AWAY. THANKS A MILLION FOR THE INFO. JIM AND SUPERDAVE666 THANKS IT WAS A VACCUM LEAK LIKE YOU GUYS BOTH SUGGESTED. MIGUEL.....