We may have more similar problems than I first thought.

I hooked up my OBDII reader again today. I was able to confirm that it's the bank 2 pre-cat sensor that is flat at 0.0 volts not bank 1. The bad signal from my pre-cat bank 2 sensor is identical to what you show in your attached pic above, flat-lined with an occasional spike to around 0.5 volts. Bank 1 is fine. The O2 sensor signal may be indicating a lean running condition, but the problem I'm having with that diagnosis is that the long term fuel trim is reasonable on bank 2 (actually slightly negative, between 0 to -4%). As far as I know, if the ECU were compensating for a lean mixture, the fuel trims should be running positive. Nevertheless, I'm going vacuum leak hunting myself. I'm concerned about the PCV connection at the back of the engine. When I removed the throttle bodies, I noted that the right side metal PCV tube that wraps around the engine was kind of floppy, which worried me. I tried having a look with a mirror, but I really couldn't get a good view to confirm that the connection in back was solid. The PCV tubes connect directly to the throttle body.

I should clarify that my car wasn't having any running issues before I went and removed the throttle bodies. My condition was just like yours, seemed to run perfectly fine. I think I buggered something up in the process of doing the throttle bodies, and it may have been the PCV hoses.

And in case you haven't checked, yet, the vacuum hose tubing is available by the foot from the dealership parts counter. I bought some a while ago.

As I said, I have switched MAF sensors with no satisfaction. I have also switched O2 sensors (In fact, I just did it again today.) with no satisfaction. Oh, and my OBDII diagnostic checks all come up completed, and usually, the fuel systems read closed loop with fault, but today as I was checking things, I was seeing "open loop driving" for a long time. I'm not sure what that means versus simply "open loop."

Please keep us informed of your progress, and I'll do likewise.

Brett

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1997 S600 sedan