Change ignicine, fuel sensor, cam position reg. mass air flow, crank sensor,coolant temp. sensor

Check your timing marks. If you haven't set the timing correctly it will not run properly (this may not apply to you as Hyundai uses interference engines but it would explain why all the sensors are reading normal but the engine has no power) Other thing to check are coil packs. If you are pulling no code errors from the ECM it should theoretically be fine. What was the reason why you replaced all the sensors in the first place? It might be something you overlooked.

The engine computer ,with inputs from engine sensors ! Mass air flow sensor , map sensor , coolant temp sensor , Throttle position sensor , crankshaft position sensor , cam sensor etc.... through software programmed into the PCM .

Have you had it to a shop that has a professional type scan tool that can view engine sensor data parameters ? Do you know what those are ? Idle air control counts , mass air flow sensor data , MAP sensor , TPS - throttle position sensor , crankshaft position sensors , Cam sensors , engine coolant temp , intake air temp etc......

Mass air flow sensor maybe ! Be nice to know what data sensor parameters are . Do you know what these are ? Your vehicle has a number of sensors that supply the engine computer with data ,signals what ever you call it ! Do won't to get to technical on you . Your engine has crank sensor , cam sensors , coolant temp sensors , intake air temp . sensor , manifold pressure sensor , throttle position sensor etc.... They have a voltage coming from the PCM/ECM - engine computer , an they send another voltage back to the computer . With progamming inside the computer it knows from these voltage signals what the temp. of the engine is etc.... With a proper scan tool you can see what the computer inputs are . Even a bad coolant temp sensor could cause the problem your having .

starting definately has a lot to do with the crank/cam position sensors, but it wouldnt have nothing to do with hot or cold weather, oxygen sensor will make the vehicle run too rich if its out, you will smell fuel very strong out the exhaust, that could make it run sluggish also, and usually if the mass air flow sensor goes out the vehicle wont start at all...

Wow these are hard to find!!

Diagnostic codes for 1987 Pontiac

13 Open Oxygen Sensor Circuit
14 Coolant Temperature Sensor (High Temp Indicated)
15 Coolant Temperature Sensor (Low Temp Indicated)
21 Throttle Position Sensor (Signal Voltage High)
22 Throttle Position Sensor (Signal Voltage Low)
23 Manifold Air Temperature (MAT) Low Temp Indicated
24 Vehicle Speed Sensor (VSS) Circuit
25 Manifold Air Temperature (MAT) High Temp Indicated
32 Exhaust Gas Recirculation (EGR) Vacuum Control
33 Mass Air Flow Sensor (MAF) (GM/SEC High)
34 Mass Air Flow Sensor (MAF) (GM/SEC Low)
41 Cam Sensor Circuit
42 C3-I EST or Bypass Circuit Failure
43 Electronic Spark Control (ESC) Circuit
44 Oxygen Sensor Circuit (Lean Exhaust Indicated)
45 Oxygen Sensor Circuit (Rich Exhaust Indicated)
51 PROM Error
52 CALPAK Error
55 ECM Error
If you have your owners manual they should be in there. I couldn't find one online but did find this.

Future reference
http://autorepair.about.com/library/ts/obd-i/bl-dtcs-28.htm?once=true&

I hope these helped you

Threepoints of interest.

Fuel pump ( can you hear it working)

Your crankshaft position sensor ( controls spark) & the

Mass air flow sensor (controls the air / fuel ratio to engine )

Good luck.

crank sensor - fromnt of engine at crank pulley
MAF sensor - 1st sensor on duct exiting the air cleaner
Fuel pump , in fuel tank.

ERROR CODE MALFUNCTION DESCRIPTION

12 ERROR CODE DIAGNOSTIC SYSTEM FUNCTIONING CORRECTLY

13 OXYGEN SENSOR CIRCUIT OPEN

14 COOLANT TEMPERATURE SENSOR CIRCUIT (HIGH TEMP)

15 COOLANT TEMPERATURE SENSOR CIRCUIT (LOW TEMP)

21 THROTTLE POSITION SENSOR (TPS) CIRCUIT (HIGH)

22 THROTTLE POSITION SENSOR (TPS) CIRCUIT (LOW)

23 MANIFOLD AIR TEMP (MAT) CIRCUIT (LOW TEMP)

24 VEHICLE SPEED SENSOR (VSS) CIRCUIT FAILED

25 MANIFOLD AIR TEMP (MAT) CIRCUIT (HIGH TEMP)

31 WASTEGATE SOLENOID ELECTRICAL SIGNAL FAILED

32 EXHAUST GAS RECIRCULATION (EGR) CIRCUIT

33 MASS AIR FLOW (MAF) CIRCUIT (HIGH)

34 MASS AIR FLOW (MAF) CIRCUIT (LOW / NO SIGNAL)

35 CODE NOT USED ON TURBO CARS

41 CAM SENSOR CIRCUIT FAILURE

42 C3I ELECTRONIC SPARK TIMING (EST) FAILURE

43 ELECTRONIC SPARK CONTROL (ESC) FAILURE

44 OXYGEN SENSOR CIRCUIT (LEAN EXHAUST)

45 OXYGEN SENSOR CIRCUIT ( RICH EXHAUST)

51 PROM ERROR

52 CALPAK ERROR

53 WATER INJECTION

54 CODE NOT USED ON TURBO CARS

55 ECM ERROR

Return to Chart
CODE 12

Trouble Code 33 and 34 are the MAF/MAP Sensor Circuit. It sounds like you've replaced that sensor already. Did you also have the code 34 before putting in the new sensor?
Or did this code start after it's replacement? Any other codes appearing?

Troubleshooting it would depend if it has the Speed Density Update. The dealer should be able to provide that info.

Here's your fault code list:

13 oxygen sensor circuit 14 coolant temp sensor circuit (high temp) 15 coolant temp sensor circuit (low temp) 21 throttle position sensor (TPS) circuit (high signal) 22 throttle position sensor (TPS) circuit (low signal) 23 manifold air temp (MAT) circuit (low temp) 24 vehicle speed sensor (VSS) circuit 25 manifold air temp (MAT) circuit (high signal) 31 wastegate solenoid electrical circuit 32 exhaust gas recirculation (EGR) circuit 33 mass air flow (MAF) circuit (gm/sec high) 34 mass air flow (MAF) circuit (gm/sec low) 41 cam sensor circuit 42 C3I EST or bypass circuit failure 43 electronic spark control (ESC) circuit 44 oxygen sensor circuit (lean exhaust) 45 oxygen sensor circuit (rich exhaust) 51 PROM error 52 calpak error 55 ECM error

Have you replaced your O2 sensor? If not, try that.