93 Lumina Euro 3.1 - Idle drops every 60 seconds.

[HomeworkWatcher]

I have a 1993 Chevrolet Euro 3.1 - it idles quite nicely at 1000 rpm but drops out when you first start to give it gas. It's like there is a dead spot just at the beginning of the throttle. Also, if you let it idle, it will run smooth for 60 seconds and then drop out to about 500 rpm and the check engine light comes on. Then it will go back to 1000 (for 60 more seconds.)

See codes below...

You can set your watch by this as it happens every 60 seconds.

Removed and cleaned throttle body and plennum to "like new", cleaned EGR, new fuel rail and injectors, new MAP sensor, new fuel pressure regulator, new O2 sensor, new catalytic converter, new TPS, new IAC, all new vacuum lines, new plugs, new wires, new coil packs, new control module, new fuel filter and of course ... new gaskets throughout. Fuel pressure tested good.

Codes - 94 3.1L VIN T MFI

33 MAP sensor voltage was too high for 4.8 seconds when throttle angle was less than 2%.

45 Oxygen sensor voltage was over 0.75 volts for 60 seconds in closed loop operation with a throttle angle between 6% and 20%.

PLEASE HELP ME SOLVE THIS MYSTERY before I torch this car! :-)

[Bearwulf]

code 45: disconnect O2 sensor and jump harness ckt 412 to grnd. Should display O2 below .35 volts. Does it?


code 33: ign. off, disconnect map sensor elec. connector.
ign. on, scan should read 1 volt or less. Does it?