bad gas milage Help

i have a 88 supra turbo gettting the worst gas milage not sure how bad it is because my spedo dosnt work but i know i just put 20 bux in and it got me like 50 miles. no egr installed i just got the car so it could be anything i just replaced wire harness and cam position sensor. getting code 43 51 52

43 - STARTER SIGNAL--NO "STA" SIGNAL TO ECU UNTIL ENGINE SPEED EXCEEDS 800RPM

--IGNITION SWITCH/CIRCUIT

--ECU

51 - SWITCH SIGNALS IDL (tps) CONTACTS OFF, NEUTRAL START SWITCH OFF, A/C SWITCH "ON" SIGNAL TO ECU

WITH DIAGNOSTIC CHECK CONNECTOR SHORTED

--A/C SWITCH/CIRCUIT

--A/C AMPLIFIER

--TPS/CIRCUIT

--NEUTRAL START SWITCH/CIRCUIT

--ECU

52 - KNOCK SENSOR SIGNAL

--OPEN OR SHORT IN KNOCK SENSOR SIGNAL

--KNOCK SENSOR/CIRCUIT

ECU

I would check/replace the knock sensor wiring/connection, and check/replace the TPS wiring/connection - and TPS if necessary. Clean the connections with electronic connection cleaner. Knock sensor wires are commonly damaged or connections dirty.

checked codes again after 1 full tank of gas and no more codes apear. still bad gass milage. new knock sensor new tps and set tps.

What about the knock sensor wiring? That gets damaged often.

you should try changing out the air filter, the fuel pump, or maybe even the pcv valve, spark plug and get a add in cleaner that you add with a tank of gas. i dont know if that would work for the supra but when ever ive had that problem with my rides thats what i have done and got great resolts.