Red88GTA

I am fighting a rich and slightly rough idle. After reading several threads on MAF readings, most do not cover what voltage readings you should get on the MAF "C" (dk green) wire. Mine unconnected gets the 5 Volts, probing the C wire connected gets 2.5 Volts. With the engine running while still probing the C wire, I am getting .8 volts at 500 RPM and at 2500 RPM, getting 1.8 volts. All the other checks look good and no SES light. Does this sound normal or could I have a contaminated MAF?

Trickster

That sounds about right.

The Trickster!!!!!!!!!!!!

Captain C

Try checking your TPS reading. The factory setting is .54 milivolts while running. Also, use electrical contact cleaner to clean your MAF. If you have reusable air filters that need cleaning and reoiling. Sometimes oil comes off the air filter and coats the MAF making it run rough, if you get enough oil on the MAF, it will throw a code.

JakeJr

The only thing I can say is that everything I've read, including the GM Shop Manual says to check and set the TPS voltage with the engine 'OFF', ignition key "ON" using jumper wires.

.54 volts (+/- .075) is the setting you're shooting for.

Jake

Captain C

Yeah, sorry about that.... That works out to .56 milivolts running. I usually have mine set at about .65.... It seems to help make up for the lean miss the miscalibrated PROM is giving me....

I haven't used a jumper. I just pushed the probes through the back of the connector......

JakeJr

I

Ignition "ON" engine stopped, connect voltmeter between Harness Terminal 'C' (CKT 998) and chassis ground. Should read between 4-6 volts.

If it's over 6 volts check for a short in CKT 998, if less that 4 volts check for open CKT 998, if not open it is a faulty ECM Connection or ECM.

Ignition "ON" probe harness terminal 'D' (CKT 994) with a voltmeter should read 0 volts.

This was taken from the GM Shop Manual for the 86 Vette.

Try spraying the sensor wires with some electrical cleaner; Turn the MAF upside down and hold it in a downward angle so none of the cleaner can enter the electronics. This helped restore mine after the K&N red filter oil coated the MAF wires.

Jake

ZZ28ZZ

Sounds like the MAF is working right.
When's the last time you replaced the O2 sensor?