I have a 99 F150 XLT 4.6L with over 185,000 miles on it. I noticed a couple weeks ago that is was starting to stumble. Whem the air temp. was below freezing truck ran great as the air temp warmed during the day the worse the truck would run. Engine light came on and the code was for an oxygen sensor. erased the code, light stayed off for about a month (truck ran about the same), when the light came back on the truck ran great. When I read the codes there was 6 different codes, P0113, P0171, P0174, P0303, P0301 and P0308. I changed the plugs, wires, fuel filter and air filter. erased the codes, took the truck for a ride engine light comes back on. Only 1 code P0303 and engine stumbling now and then. I noticed that when the truck was in gear there was I tapping sound and everytime I heard the tap the engine would stumble. I pushed all the spark plug wires and when I pushed #8 ticking stopped. Went for another ride, truck runs great, come back shut truck off, restart no ticking but have code P0308 and the truck is running very rough. Next morning going to work truck runs great on the way home truck runs rough about half way home then starts running great again. Now I have P0303 erase code checked the Coil packs both read fine. Start truck, truck stalls now I have P0303 and P0113, erase codes check IAF reads fine, start truck stalls and only have P0113 code. Right now the truck wont run for more then 15 seconds. Anyone have any idea whats wrong and why the codes keep changing? Im leaning towards the MAF, does that make any sense?

On a side note, How much would you sink into a truck with 185,000 miles. Value of the truck is probably around $2000. I have spent over $150 trying to fix the problem above and over $100 on a used brake booster and Master cylinder. Anyone have a opinion on this?