These codes are for the 4AGE (AW11 Normally Aspirated) and were taken from the USA manual for the 1988 AW11 MR2 covering both Normally Aspirated and Supercharged models.

Code:	System	Diagnosis	Trouble Area
-	Normal	This appears when none of the other codes are identified	-
12	RPM Signal	No "NE" signal to ECU within 2 seconds after engine has been cranked. No "G" signal to ECU 2 times in succession when engine speed is between 500 rpm and 4,000 rpm.	Distributor circuit Distributor Starter signal circuit Igniter circuit Igniter ECU
13	RPM Signal	No "NE" signal to ECU when engine speed is above 1,500 rpm	Distributor circuit Distributor ECU
14	Ignition Signal	No "IGf" signal to ECU 4 times in succession	Igniter circuit Igniter Igniter and ignition coil circuit Igniter and ignition coil ECU
21	Oxygen Sensor Signal	Detection of oxygen sensor deterioration	Oxygen sensor circuit Oxygen sensor ECU
	Oxygen Sensor Heater	Open or short circuit in oxygen sensor heater	Oxygen sensor heater circuit Oxygen sensor heater ECU
22	Water Temp Sensor Signal	Open or short circuit in water temp. sensor signal (THW).	Water temp. sensor circuit Water temp. sensor ECU
24	Intake Air Temp. Sensor Signal	Open or short circuit in intake air temp. sensor signal (THA).	Intake air temp. sensor circuit Intake air temp. sensor ECU
25	Air fuel Ratio Lean Malfunction	When air-fuel ratio feedback compensation valve or adaptive control value continues at the upper (lean) or lower (rich) limit renewed for a certain period of time.	Injection circuit Injector Oxygen sensor circuit Oxygen sensor ECU Fuel line pressure Air leak Air flow meter Ignition system
26	Air-fuel Ratio Rich Malfunction	When air-fuel ratio feedback compensation valve or adaptive control value continues at the upper (lean) or lower (rich) limit renewed for a certain period of time.	Injector circuit Injector Oxygen sensor circuit Oxygen sensor Fuel line pressure Air flow meter Cold start injector ECU
31	Air-Flow Meter Signal	Short circuit between VC and VB, VC and E2 or VS and VC	Air flow meter circuit Air flow meter ECU
41	Throttle Position Sensor Signal	Open or short circuit in throttle position signal	Trottle position sensor circuit Throttle position sensor ECU
42	Vehicle Speed Sensor Signal	No "SPD" signal for 5 seconds when engine speed is above 2,500 rpm	Vehicle speed sensor circuit Vehicle speed sensor ECU
43	Starter Signal	No "STA" signal to ECU until engine speed reaches 800 rpm with vehicle not moving	IG switch circuit IG switch ECU
*71	EGR System Malfunction	EGR gas temp. below predeterminal level for during EGR control	EGR system (EGR valve, EGR hose etc.) EGR gas temp. sensor circuit EGR gas temp. sensor VSV for EGR VSV for EGR circuit ECU
51	Switch Signal	Air conditioner switch ON, idle switch OFF or A/T shift position other than "P" or "N" range during diagnosis check	A/C switch circuit A/C switch A/C Amplifier Throttle position sensor circuit Throttle position sensor ECU

* For California (This may still apply as Japan had similar strict emissions laws)

These are taken from the site http://www.off-road.com/toyota/tech/codes/ and are general Toyota engine codes. These MAY help you in tracking down a problem.

ONE-DIGIT	TWO-DIGIT	POSSIBLE CAUSE OF CODE/SYMPTOM
	NONE	SYSTEM NORMAL
--	11	LOSS OF POWER SUPPLY TO ECU --IGNITION SWITCH/CIRCUIT --MAIN RELAY/CIRCUIT --ECU
6	12	RPM SIGNAL-NO SIGNAL TO ECU FROM DISTRIBUTOR ("Ne"OR "G") AFTER ENGINE HAS BEEN CRANKED --DISTRIBUTOR/CIRCUIT --STARTERSIGNAL CIRCUIT --IGNITER/IGNITER CIRCUIT --ECU
--	13	SAME AS ABOVE BUT AFTER ENGINE HAS RUN AT 1,000-1,500 RPM --DISTRIBUTOR/DISTRIBUTOR CIRCUIT --ECU
3	14	IGNITION SIGNAL--NO "IGF" SIGNAL TO ECU --IGNITER/IGNITER CIRCUIT --IGNITER AND IGNITION COIL/CIRCUIT --ECU
5	21	OXYGEN SENSOR SIGNAL/OXYGEN SENSOR HEATER SIGNAL OPEN OR SHORT IN OXYGEN SENSOR OR OXYGEN SENSOR SIGNAL
4	22	WATER TEMPERATURE SENSOR SIGNAL--OPEN OR SHORT IN WATER TEMP. SENSOR SIGNAL --WATER TEMPERATURE SENSOR CIRCUIT --WATER TEMPERATURE SENSOR --ECU
8	24	INTAKE AIR TEMPERATURE SENSOR SIGNAL--OPEN OR SHORT IN INTAKE AIR TEMP. SIGNAL --INTAKE AIR TEMPERATURE CIRCUIT --INTAKE AIR TEMPERATURE SENSOR --ECU
--	25	AIR/FUEL RATIO LEAN INDICATOR--LEAN SIGNAL SENT TO ECU FROM O2 SENSOR --INJECTOR FAULT(S) --FUEL PRESSURE --OXYGEN SENSOR --AIRFLOW METER OR MAP SENSOR --IGNITION --ECU
--	26	AIR/FUEL RATIO RICH INDICATOR --SAME AS ABOVE --COLD START INJECTOR
--	27	SUB-OXYGEN SENSOR CIRCUIT OR SUB-OXYGEN SENSOR HEATER CIRCUIT --SUB OXYGEN SENSOR/HEATER/CIRCUIT --ECU
--	28	No.2 OXYGEN SENSOR/OXYGEN SENSOR HEATER --SAME AS CODE 21
2	31	MANIFOLD AND/OR AIRFLOW METER SENSOR SIGNAL CIRCUIT --AIRFLOW METER/CIRCUIT --MANIFOLD PRESSURE SENSOR/CIRCUIT --ECU
--	32	AIRFLOW METER SIGNAL (VANE-TYPE) --AIRFLOW METER./CIRCUIT --ECU
14	34	TURBOCHARGER PRESSURE--ABNORMAL TURBOCHARGER PRESSURE --TURBO CHARGER --AIRFLOW METER/MANIFOLD/TURBOCHARGER PRESSURE SENSOR --INTERCOOLER SYSTEM --ECU
--	35	TURBOCHARGER PRESSURE SENSOR SIGNAL --TURBOCHARGER PRESSURE SENSOR --ECU
7	41	THROTTLE POSITION SENSOR SIGNAL--OPEN OR SHORT IN TPS SIGNAL --TPS SENSOR --TPS SIGNAL/CIRCUIT --ECU
9	42	VEHICLE SPEED SENSOR SIGNAL CIRCUIT--NO SPD. SIGNAL FOR SEVERAL SECONDS WHILE VEHICLE IS OPERATED UNDER HEAVY LOAD (TPS/MAP/AIR FLOW INPUTS) --SPEED SENSOR/CIRCUIT --ECU
10	43	STARTER SIGNAL--NO "STA" SIGNAL TO ECU UNTIL ENGINE SPEED EXCEEDS 800RPM --IGNITION SWITCH/CIRCUIT --ECU
11	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
12	52	KNOCK SENSOR SIGNAL--OPEN OR SHORT IN KNOCK SENSOR SIGNAL --KNOCK SENSOR/CIRCUIT ECU
13/CENTER>	53	KNOCK CONTROL SIGNAL IN ECU --ECU
--	71	EGR VALVE MALFUNCTION--EXHAUST GAS TEMPEATURE BELOW SPEC. FOR EGR CONTROL --EGR SYSTEM --EGR GAS TEMPERATURE SENSOR/CIRCUIT
- -	72	AIR CONDITIONER COMPRESSOR RELAY/RELAY SIGNAL --A/C COMPRESSOR RELAY/CIRCUIT --ECU

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