2000 Focus, Rough Idling in Signals and now P171 code appears

I have rough idling problems for a while, when ever I stop in Signal, If I press the gas it goes off, Cold start is fine, now Check engine sign is on and shows p171, system too lean (bank 1)
I had this problem before and I cleaned MAF sensor and cleared the codes (i forgot how i cleared it) and it was fine but now it re appears.
I had changed fuel pump a month back no healp.
I have 77.5K miles on it, I dont want to spend a ton of money on it.
I see some one one suggested this could be due to vacuum leak?
Any easy solution? would adding fuel additives help?
Pls Let me know

Thanks

I have rough idling problems for a while, when ever I stop in Signal, If I press the gas it goes off, Cold start is fine, now Check engine sign is on and shows p171, system too lean (bank 1)
I had this problem before and I cleaned MAF sensor and cleared the codes (i forgot how i cleared it) and it was fine but now it re appears.
I had changed fuel pump a month back no healp.
I have 77.5K miles on it, I dont want to spend a ton of money on it.
I see some one one suggested this could be due to vacuum leak?
Any easy solution? would adding fuel additives help?
Pls Let me know

Thanks
rough idle could be caused by a miss,MAF, or vac leak
buy a can of brake cleaner or starter fluid and spray it around vac lines throttle body, intake gaskets, etc.

mine did the same thing. i just replaced the vacuum hose on the back of the engine for like $20 and it was fixed

I am a novice with cars, is there any site or DIY instructions to replace Vacuum hose? or from a manual.

First you find the leak by spraying or visually checking the hoses. Then you check the size if it and buy a replacement piece at the auto store.
They are just air type tubes on the engine used for different purposes going different places usually from a center location.

A vaccuum system is a closed air source of low pressure air used to move valves such as heater vents and diaphrams in cruise controls and not to outside air. Unfortunately if they leak they leak outside air back into the engine and lean out the gas mixture.

Good luck

I have a 2003 Focus SE - same problem. Took it to the dealer after exhaustive hours under the hood and cussing. They found the PCV Valve Elbow Hose had a hole that you can stick your little finger in. Apparently a common problem on Focus models that I have been reding in this forum from other users. Most have been temporarily fixing this by using duct tape to patch the hole until the proper elbow hose part can be ordered from Ford. No, unfortunately you can not get PCV Valve & its accosiated parts from Advance Auto Parts, Autozone, etc. It can be accessed by following the hose that comes off your valve cover (the top of the engine where you put your oil in) on the upper right-hand side of the engine as you face your car. This hose goes under a larger hose (from your air cleaner housing to the top of the intake) and bends down towards the back of the engine compartment on the left-hand side. At the bottom of this hose is this magical PCV Valve Elbow Hose, which can be easily disconnected by pulling gently on the PCV Valve hose you just traced out. Remove the other side of the PCV Valvw Elboe Hose from whatever it is attached to and see if it has a hole in it. I am going to attempt this duct tape trick and see what happens.