When cold, and I start it up, it runs really rough, RPM drops to about
500, and it stalls. When it warms up, it runs better when idling.I put a jumper across pin 29 on ECU (oxygen sensor) and it shows .2 volts (lean mixture). When it warms up, and I run it up to 2000 RPM for 2 minutes, pin 29 still shows .2 volts, and it won't go into closed-loop mode. When I race the engine, and then come back to idle, sometimes the pin 29 voltage swings up to 1.3 volts, then back to .2 volts. When I race the engine, and then come back to idle, sometimes the pin 29 voltage stays at .2 volts, and doesn't vary. Sometimes, when I race the engine, and drop back to idle it goes into closed-loop mode, and sometimes not. That is, I put the ECU into mode 2, and the green light flashes. When it does go into closed-loop mode, and the green light flashes in mode 2, the right light stays lit the whole time (lean mixture).
When I disconnect the MAF plug, the pin 29 voltage (oxygen sensor) goes up to 1.3 volts, and the car runs fine at idle, both when hot & cold. I reconnected the MAF plug, and measured the pin 27 voltage (MAF sensor), and it is within specs ( 1.3 volts at idle, and 1.8 volts at 3000 RPM ).
The car seems to run fine with the MAF plug disconnected, but the MAF sensor doesn't seem to be bad. With the MAF plug connected, the car seems to run lean, and sometimes won't go into closed-loop mode. When I does go into closed-loop mode, the red light stays on the whole time in mode 2, indicating a lean condition.
The possibilites I come up with are:
1) Bad ECU 2) ECU pin 27 (MAF sensor): bad connection between harness and ECU pin, so that ECU is not getting correct MAF sensor input.Thanks in advance for any thoughts, ideas, or other diagnostic suggestions.
Thomas