I have a 1988 IROC Z28 with standard 305 TPI engine. It has been running rough and often shuts-off as though the ignition were simply turned-off (even when at cruising speed). It indicates a code 34 - problem with the signal of the Mass Air Flow Sensor. We've replaced the sensor with a remanufactured one and saw no change. I tested the factory sensor and found that the highest DC voltage output I could obtain (about 40 degree F and fairly humid day with car reved to high rpms) was about 1 1/2 volts. I read somewhere that the output should be something like 4 1/2 volts under these conditions. Is there a way to adjust (calibrate) the output of the factory MAF sensor? (Note: computer, Oxygen sensor, throttle position sensor have already been replaced)

Also strange - The car always runs great the first trip that's taken after the battery has been disconnected! It will run fine and show no service code until the engine is shut-off and restarted. Then it will immediately begin to idle rough and shut-off at the most inconvenient times.

Doesn anyone know the answer?

 

I also have a 1988 IROC that does excatly the same thing your car does. Including the running fine after a computer reset, code 34, and random stalling. I replaced my maf and all the relays, computer , and other misc sensors with no luck to date. My car has not run properly in over a year. I had 2 mechanics look at it and they cannot figure it out either. So I give up and I am coverting to Speed density when I do my motor swap.

Sorry, I am not much help. But if you figure it out please let me know. Run a search and you can probably find some of my old threads on the issue.

I am baffled by this problem and swear this occurs more frequently on 88 model year cars and that there is a factory defect somewhere.

 

Try replacing the relays for the MAF. There are 2 of them. Also check the wiring.

 

I already checked the relays. The car had also been giving a code 36 which means the burn-off relay or circuit isn't working. I tested both relays and found the burn-off relay wasn't closing its contacts when energized. I replaced it and the code 36 went away. I had already checked the wiring as well.

I'm thinking about putting a relay in the power supply circuit to the computer so that whenever the car is shut off, power to the computer shuts off as well so that it resets itself and works for each time the car is driven. Hate to do this but I can't think of any other options.

Keith

 

Have you checked the connectors at the ECM?? I have seen cases where the coolant temp sensor fails (no code, still works, just leaks) and coolant will wick up the harnes to the ECM, and cause no end of interesting, unsolvable issues. Given the nature of the low voltage sensor circuits, it does not take much in the way of corrosion to really screw up the signal.

 

Try this chart for your code 34 and see if it helps any.

 

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This is the car owner who started this thread speaking.

The cause of the problem has been found and it was not a big thing.

The MAF was not the problem! It was working fine all-along. The car showed a Code 34 ONLY BECAUSE OF A ROUGH IDLE! Thanks to the guy that posted the diagnoses procedure with diagrams, this was found! (Note: The MAF is supposed to receive a 5V power supply from the ECM. When I measured a low voltage as stated in my original thread, I didn't have my test set-up properly).

Now for the fix: The cause of the car shutting-off unpredictably at any speed was a BAD IGNITION PICK-UP. In addition, This car had a weak ignition coil that was making it start hard and not run as smoothly as is should. The ignition coil problem had been found first and the car stopped giving the Code 34 once that was fixed but continued to shut-off unpredictably. Once the pick-up was replaced, the car ran like new. (and continues to run like new)

Thanks to everyone that provided information in this thread!

Keith
Seven Valleys, PA

 

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