codes P0171 and P0174

[willrapppold]

i have a 99 explorer xlt 4.0 SOHC with 145000 miles on it. I have a rough idle on initial start that gets worse the colder it gets (dose it a little in summer but winter time its horrible) I have had this truck for 3 years and this problem has slowly gotten worse to now its pulling up these codes for being to lean, it also has a little erratic idle after driving. I have cleaned my air flow sensor, have a clean k/n air filter, and replaced the fuel filter and have been using lucas oil gas treatment, but the truck hasn't gotten any better. I am now going to look for split vacuum hoses, does anyone know where the pcv valve is located or which lines i should be looking for? I'm trying to cover the little things before i have to go the expensive upper/ lower intake gasket route. thanks.

 

[koda2000]

You need to replace your intake manifold O-rings. Very common issue with the SOHC engine. With age, the O-rings dry out and shrink creating air leaks. This is worse in the cold as parts contract and the air leaks are worse. As parts warm they expand and the leaks become less.

 

[reeko]

I would check your IAC, and its gasket, It's really easy. Also, since the codes say bank 1 and 2 are lean, sounds like you're going lean on all cylinders. If your intake gasket was cracked, I would assume that you'd only be lean on whatever side is cracked. Have you tried using a "spray test" to locate possible vacuum leaks? Its simple, just spray something (wd40, carb cleaner, etc) around the intake and vacuum hoses, when you spray on a leak the idle should go back to normal or change, because the leak is temporarily blocked by whatever you're spraying. Good luck, keep us posted.

 

[willrapppold]

yea the funny thing about the check engine light only comes on when like now when it gets down in the 30s-40s early in the morning, when i drove the truck this weekend during the day between 50-65 degrees i still had some rough idle, but no engine light.

 

[Scout3]

Had the exact same issue. Only happened when it was cold out. Changed upper and lower intake gaskets and o rings and problem never came back. Not expensive and not terribly hard to do yourself.

Ed

 

[chefduane]

Ditto what Scout said. Same symptoms, same codes, same fix, on my '98 SOHC 201k miles. Did upper & lower mani gaskets and problem solved. RA has Felpro sets for like $12.

 

[45Frank]

I would check your IAC, and its gasket, It's really easy. Also, since the codes say bank 1 and 2 are lean, sounds like you're going lean on all cylinders. If your intake gasket was cracked, I would assume that you'd only be lean on whatever side is cracked. Have you tried using a "spray test" to locate possible vacuum leaks? Its simple, just spray something (wd40, carb cleaner, etc) around the intake and vacuum hoses, when you spray on a leak the idle should go back to normal or change, because the leak is temporarily blocked by whatever you're spraying. Good luck, keep us posted.

Took mine in today for same codes. Mechanic did the spray test and nothing. Put computer on record or something like that and said bring back in the morning after driving 40 or so miles. I'll see tomorrow morning.

 

[ExpoinLA]

Installed my K&N, got the codes.. swore it was from the filter. Weeks later I had an idle issue and replaced the gaskets.. no more codes. Just sharing my experience.. once again gaskets. I'm still getting a little rough idle with the A/C on parked.