1993 Corolla runninh RICH.. 50% mileage decrease

[dukeduster]

Well I have a 93' corolla that I've changed the engine in. It had original 4AFE in it and was blown up. I bought another 4AFE from a junkyard that came from a newer Geo Prizm. It ran fine averaging about 35-40 MPG. I then SUDDENLY had mileage drop to about 15MPG. Engine idles rough and smokes black at idle. Changed plugs and rotor. Small improvement if any. under full throttle I can feel the engine has no power for about 2-4 seconds and then all power restores and runs fine till throttle is let up. Being this is a OBD1 car. Does the O2 sensor control A/F mixtures to the extremity that I am seeing?

[1jzdreamer]

tps. I think you have a bad tps or map sensor. either one reading wrong will tell the computer you have too much air or that your pressing the throttle further then you actually are. Id check them with a meter and go from there. The o2 sensor does control a/f but only to a very minimal point. Id say it will affect your fuel mileage on these cars maybe by 10-15% only and driveability wouldn't be affected.

[lee777]

Check that fuel pressure regulator has vacuum line hooked up.
Check all other vacuum hoses.