hey you guys im new to this forum so any help would be great! i have a 1991 f150 302 v8 5.0 1/2 p/u 4wd EFI and when it starts it takes a few cranks. after it starts, it idles really bad then dies unless i give it gas. i have replaced the fuel filter , air filter, oil filter, oil, all fuses, oil sensor, battery, and i had the gas tank cleaned. fuel pump on the back tank is burned out. front tank works fine but still dies when i give it gas . and when i am driving it wont get past 10mph. and slows down and sputters then when i let go of the gas the sputter stops and it will go back to 10 mph. i took all the spark plugs out and checked them . they were all original plugs . every gap was different between the 8 of them so im am gonna get new spark plugs. would the spark plugs cause it to not go faster than 10mph? if not what else could it be . thanks so much ahead of time.

 

Cap & rotor,cats, vaccum leak.

 

23 year old spark plugs?????? No brainer, replace them. Do the cap, rotor, and wires while you are at it and get your cats tested for blockage.

 

After you've done all that, check your MAF sensor if you still have problems with the engine falling on its face when you hit the gas.

 

Considering the plugs and your probable stupid fuel mileage...CATS can also go to crap after that much raw fuel has gone through there.

 

I think it's speed density, not a mass air engine. So, that could be the MAP sensor.