Code 33 but MAF ok
 

I'm having a somewhat intermittent issue with my 1989 Corvette where the engine cuts back to idle when the car is in gear and the throttle is pressed to approximately 20%. If held there the SES light will come on after about 5-6 seconds and a code 33 (high voltage MAF) will be stored. The problem is worse on the highway and it will often "cut back" when the throttle is just off idle. If I let off the throttle the engine comes back to life again and will run normally. If I push the throttle from idle past the 30% mark (approximately) then the car accellerates fine and runs very well. If the engine "cuts back" and I push the throttle further the car will spit and sputter and will run very poorly with no performance until I lift my foot and then the car will come back to normal.

It's as if the computer is reading the high voltage at the MAF below 25% throttle and below 2200 RPMs like it should, however changing out the MAF isn't working. Changing out the the MAF supply and burn off relays made no difference either. I've checked all the wires from the MAF to the ECM for continuity and shook them around during the test and no problems there. I've also switched out the TPS and it made no difference.

Has anyone had this issue before? Any ideas?

Thanks,
Andrew

Need to check your supply voltage to the MAF and check grounds. Loss of a ground will cause MAF voltage to go high.

Had the same problem on my 1988 Formula 350 F/bird. It was the Maf burn off relay. Not expensive and it cured the problem.

1989 corvette is very old... go to mechanic... most of its parts are now not sold.. use some alternatives...

Here is a wiring diagram attached the MAF. Check your voltage from the MAF relay, not the burn off relay, as it is for cleaning contaminates of the hot wire sensor after engine shut down. Check for voltage from MAF relay and check ground with an ohm meter.

my 1990 doesnt have a maf on it but mine did the same thing awhile back it was the o2 sensor

I've tried a different MAF sensor as well as different power and burn off relays but the problem is still there. I bought the cable to link the diagnostic connector to a laptop and then I went for a drive with the computer logging the ECU information. The MAF sensor reading would spike from time to time, causing the engine to cut back to idle and when I looked through the data there were times where the O2 sensor reading went to zero. Since the car is put away now for winter I'll buy a rebuilt ECU and try that out in the spring. It seems that all electrical connections are very clean as this car doesn't look like it's even seen much rain in the past 20 years. I'll let you know how it turns out. Thanks for the replies and if you can think of anything else please let me know.

i would try the 02 sensor first like i say mine did the dame thing for months finaly chanced the 02 sensor & it cured it i would be intrested in knowing more about this cable you bought & any program needed to run it on a laptop

The O2 sensor had been changed by the previous owner to try and fix the problem but no difference. I actually have all the old parts that he swapped out to try and fix this issue. The cable is one I ordered from this site http://www.obd2allinone.com/sc/detai...item=aldlobd1u and I downloaded the Datamaster free program to monitor and log all my data. I then converted the text file into an excel spreadsheet to read it easier and there I can watch everything that my computer was seeing.

Again, check grounds and voltage supply.