I am a new user on here but own 2 trackers and have rebuilt the motor one one before. That all being said i am used to obd2 and wax pellet IAC's and the rest of the tracker quirks have me over my head. I have a 1990 chevy badged, 5spd 4x4, AC (Unbelted) with minor mods, but nothing to engine just an inch on suspension and flipped front strut mounts. I have replaced the plugs (Ngk), wires, O2 (Single Wire), Air Filter, Idler and Timing Belt, Rotor and Cap, Adjusted Valve Lash, Replaced Fan Clutch (3rd Times a charm, thanks autozone) and master cylinder, and vacuum lines (one at a time, i have GM service manual and GM Parts catalog for reference and they seem correct with no leaks, Air Temp, Water Temp, Thermostat (180) and water pump. Timing is to spec (with a guilty conscience after reading on here about jumping pins somewhere?!) CEL works, found out about the switch when i rolled over 100k, has 101k and i am second owner, Cali car whole time and all maint. Records from Dealership the old man took it to. All this stuff aside, a figured a couple hundred bucks and some work would be a great peace of mind in terms of reliability, but i cant get it to get more than 16MPG, it has 1 inch spacers and 235/75 r15's, Goodyear Wranglers and thats it. Had terrible shimmy with hardtop on at 45mph and none without so i got it aligned and tired re balanced. So all in all, i haven't delved terribly deep as i don't Fully understand TBI, and am ready to try and figure this out. Any help is appreciated, i have just about any tools for diagnosis. Issues i noticed where the IAT sensor was damaged so i replaced it, ran really cold until the fan clutch was replaced, valve lash wasn't terribly off and was adjusted cold than checked hot, good. Idles at 1500 cold, takes 4-5 minutes to warm up, then idles at 1000-1100 after driving it around. Runs fine, seems to have power, backfires when cold if i try to accelerate quickly. No CEL and EGR seems to work and exh not cracked, Cat works and passed smog with 1100 rpm idle, trying to figure this out. Ask away and ill get back same day, thanks in advance guys.