horrible gas mileage why???
 

i just swapped the motor in my truck because it was blown and i thought the reason for the gas mileage was because of that. well now i swapped and its still bad....i changed the MAF sensor and it runs a little better but im still gettin about 12 mpg the motor is a 22re and its a stock 2wd 93. now the truck idles high and if i hit the brakes it idles down then back up and down repeatedly. this thing is startin to piss me off....i tried everything, cleanin the intake , MAF, timing, i dont know what else to do, please someone give me some ideas....

well the idleing high thing and brakes has been covered a BILLION TIMES, but ill say it again lol.......with the motor idling high (above 1K) when the brakes are hit the ECU shuts the injectors off for a sec to idle down the motor...so when the idle is set high it just does this repeatedly so idle her down to 750-800 and should be good, and with the idle right should get a lil better gas mileage 0_o also try this trick

"Ok ready, first pull off the efi fuse for a couple of seconds, then reinstall it. Grab some Autolite #65 plugs, and side gap them at .048. Set the valve clearance to .011 cold. Install the factory carbed thermostat {Pappy: it's a 180* vs. 190*). Adjust the AFM 3 teeth rich (under 5000 a.s.l.). Start the motor, let idle till you reach operating temp. Set the timing at 16* "not short circuted," {Pappy: about the same as 8* shorted} then take it for a putt, re check the timing, and enjoy. Leave the airbox alone, for it's not a cause of starvation on a stocker, and don't worry about the muffler for now. If you're going to modify the exhaust, start with a header, and 2.5" headpipe."

and an explanation for all of it

"... you pull the EFI fuse to start the ECU's regathering of fuel mixture readings, because you are altering them via the AFM. The #65's are a hotter plug, and will in this case create a more efficient burn. You WILL NOT detonate when the timing is set 16* NOT SHORT CIRCUTED, because the end reading when short circuted will be 8* advanced. The afm adjustment enrichens the motor aproximately 3cc. This is necessary due to the timing advance, which requires a proper mixture."

I found the AFM 3 teeth to be too rich for my high desert home (driveway is 5200 ft) and have backed it down to 1 tooth rich.

If you are running a cat check that and the 02 sensor both can be a cause that will lead to bad fuel mileage if they are shot