I have a 85 iroc with the TPI 305 and i have had 2 different mass air flow sensors on it sense i have bought it, but it keeps showing code 34. The light only comes on when iam in drive and stopped at a light and when the car is in park just idling. The RPM's will get very low then the check engine light will come on. People have told me you have to change the BURN OFF RELAY when you change the mass air flow sensor and i havent so could a bad burn off relay cause a mass air flow sensor code.
THANK YOU MIKE

 

i am pretty sure that there is a mas module under the dash by the ecm that is burnoff relay. i would just convert to speed density. I have an 85 iroc tpi that had very similar problems and i worked on it forever and the only thing that fixed it was just getting rid of the 870 ecm b/c they suck. It was a tenfold improvement when i converted. idle, throttle response, no more stuttering when accelerating hard, no more codes related to maf, started within half a second of cranking instead of 15-20 seconds.....definately worth it. don't waste your money on a maf relay, mas module, or maf. just go SD

 

Would it be easier to go to the 86 and new mass air computer instead, also how hard is it to swap to speed density.

 

Check your TPS voltage......

 

Ok, its just weird i can drive the car all over and it is fine Intel i come to a stop and then the check engine light will come on or if i stop somewhere and leave the car running and its in park it will come on. If i come to a stop though and keep alittle bit of pressure on the gas the light wont come on.

 

Duke,
YES!

If the MAF does not accomplish a burn off of the sensing hot wire, the debris and film of dirt that accumulates on the hot wire will insulate it. This will cause lower detected input air mass, since the wire will not dissipate heat proportional to the mass of air moving through the sensing tube.

That's why there is a burn off cycle in the first place.

As GTA suggests, check teh TPS voltage as well, to be sure teh ECM is getting the correct throttle data and doesn't epect higher than indicated input flow.

 

Wouldnt i also get a code for a bad burn off relay to though.

 

Probably. But the '85 TPI ECMs are a little different. I'll be the first to say that I don't have a good grasp of their operation and programming. I do know that their diagnostic ability is pretty limited. Since the burn off feature is incorporated in the MAF slave module, I'm not sure. If you have an oscilloscope, you can test the MAF output to make sure it is relative to intake air.

There are also other items that can contribute to a '34'. That DTC simply means that the ECM has detected a lower intake air mass than is epected at a given engine RPM and throttle angle. The throttle angle is reported by the TPS, and that's the reason for veriying its setting. The RPM is reported through distributor reference pulses generated by the pickup/reluctor and conditioned by the HEI module. Presuming you aren't experiencing misfire, I'd tend to discount the distributor reference as a problem at this point.

Additionally, there are other conditions that can cause a perfectly good MAF sensor to read low intake air. Any leakage between the MAF sensor housing and the throttle body will cause a lower MAF reading. A poor electrical connection at the MAF can do the same. Leaks in the throttle body, plenum, intake, vacuum hoses, PCV breather, and EGR can skew the MAF readings toward the low end. All air entering the engine MUST be metered by the MAF. GM issued a TSB on leakage of the intake air resonator boxes for early TPIs. The intake ductwork and flexible bellows need to be inspected closely for cracks, splits, and leakage. Since the error apparently occurs only at low RPM, I would suspect a leak in the ducting or loose MAF clamp or connection.

 

I can't emphasize on this enough. DO NOT GO PURCHASE A NEW MAF SENSOR!!!. The realys and the wiring should go bad first, especially if you have kept the screens on it. I have even seen an 02 sensor set off the 34 code. Here is a way to check it and see what is causing the problem:

Sorry dude the search is still disabled. Maybe someone knows where this discussion is. Start a new post in TPI, they know where it is.

 

I have looked at the connections and they are good and there are no crakes that would let air in. The car has newer O2 sensors, and the Mass air sensor is about a couple months old. There are also new fuel injector O rings, and plenium gaskets. So iam stumped. The TPS was set about a month or so ago also.

 

After you replaced the MAF did you immediately get a code or did it take a while. If it took some time then Vader is probably correct in saying you may have a burnoff issue. The hotwire in the MAF will quickly get contaminated if burnoff does not occur. DO NOT consider going to MAP(speed density)as a way to resolve your problem. It is not as easy to do as it sounds and MAP is not as effective at engine management. Bosch some time ago issued a technical publication stating they were not going to be designing electronic engine management systems using MAP control. Whether they went the course i don't know. MAF provides faster and better metering of incoming air. GM got away from MAF for a couple of years or so and went back to it on the LS1. It is strictly a cost issue on the part of the manufacturer as to whether they use MAF or MAP. MAF adds money to production cost. Since you have money tied up in a new sensor it may just pay to let a dealer at least diagnose it for you. Most GM dealers will diagnose a management problem for around $85 or so. You can always do the fix yourself.

 

Well, the last Mass air i put on was about 6 months ago, and it would throw the good every once in a while but in the last 2 months it comes on everyday. This code as shown up sense i bought the car 2 year ago. Thats why i bought i new sensor then i kept getting the code so i bought another one.