91Olds 88 Royal - New O2 senser gives code! HELP Pls!

In case my sig isn't attached, my car info is.
1991 Olds Eighty Eight Royal V6 3.8L 3800
126000 miles

I've been working on bad fuel economy for a few months now and it keeps coming down to the same glitch that is driving me nuts. None of the searches have led me to a solution, though two other things ended up getting fixedin the process. :Wink:
Please read all, as everything I've done and know, is included here.

Simply put, my new premium O2 sensor (single wire type) is giving me a code 13. (O2 Sensor or Circuit). My old sensor was giving me a lean exaust code, but that since hasn't returned. Fuel economy has continuted to get worse, and the voltage on the new sensor shows high most of the time. Exhaust fumes were very strong in odor, but not an unusual odor. Just an unusual amount.

My first fix before any O2 sensor problems was installing a new Cam Position Sensor. That wasn't the problem from the Code 41, and I found that I had to replace the magnet. Once that was done, the code 41 dissapeared, and the engine gained some power. Sweet.

Then I start getting a lean exaust on my O2 sensor. So, I replace the sensor. After a week, the new sensor gives me the code 13. After some reading, I learned to test the voltage of the sensor, and found that after the car warmed up, the voltage showed between.6 and.9
This code 13 never appears while idling, and the voltage stays between.3 and.6.
While driving, or while holding the RPM up a bit, after a few minutes I get the code again. If I'm holding the RPM's up without driving, the second I let my foot off the gas, the light goes out. Raise RPM's, after a minute the light comes back.

I started testing out other parts of the system. Charcol canister seems fine, Digital EGR valve got cleaned out and gaskets changed, seems to be working fine. The first reinstall of the EGR valve wasn't correct because it was blowing out air, but that was simply a gasket problem. Tested the three EGR solenoids, all checked out. MAF sensor was checked, appears fine as far as I can tell. All vacuum lines are in good shape, and I can find no leaks or fuel oders within the engine compartment. Exhaust pipes appear fine with no cracks, rust, or damage. Checked spark plugs which were replaced a year ago when I bought the car and they still look new with only minor signs of use.

When testing the throttle position sensor, it looked to be putting out voltage just as it should. However, when I tapped on it lightly (and yes, lightly) to check for any fluctuations in the voltage, the darn thing just quit. Totally quit, dead. Once I determined it was a gonner, I took it off and took it apart to see how it worked. (I love to learn) I found the small round plate that controls the voltage amount cracked in 8 pieces. So.I found a bad part, by making it worse. It has a brand new one now, and it's adjusted to the correct idle voltage.

Still, the problem with the O2 sensor returns. The line from the Sensor and ECM is fine. This is what I see while monitoring the voltage of the sensor. While idling from a cold engine (without increasing the rpm's at all) I'll get a reading of about.2 to.5. Mostly it's the lower. But, once I rev the engine and hold it, the voltage drops to Zero for a second, then comes back up and slowly rises to.8. (.9 at it's highest) There are almost always no fluctuations in current while at a steady idle, or steady hight RPM.

Keep in mind, that I get these same results regardless of whether I'm sitting in the drive way, or driving down the road. I've monitered it both ways many times.

I know that the voltage should normally fluctuate rapidly, from low to high. I've only seen it do this on two occassions, and it only lasted a few minutes. Then, I got the sense that I was seeing some real action as it is supposed to be.

In frustration, I installed the old O2 sensor. That darn thing gives me no voltage at all. No matter how hard I try, the thing won't work. Strange thing is.I noticed that even though I can't get a voltage from it at all, it won't Set a trouble code. (Keep in mind, I clear the codes for each new test)

So, I unplugged the sensor from the harness, dissconnecting it from the EMC, and although the sensor still appeared to be dead, I still never got a code.

So. With the new sensor back in, I ran the car with it hooked up, and got the code 13. I clearned the codes, tried again with the sensor unplugged, and no codes at all, however monitoring the sensor while disconnected from the ECM did give me the same high voltage as always.

I also disconnected a vacuum line (the one to the charcole canister operated by a solinoid) and just as expected, the voltage dropped down to about.1 Plugging it back in, it went back to high. Previously, Ive left that vacuum unhooked, but it didn't make any difference once I started driving or raised the RPM's. Still get the code eventually.

So, that's where I stand on this thing, and I can't figure it out. The only things I haven't checked is the Air Intake Valve, though it looks fine, the Knock Sensor which I can't locate, and the Coolent Temp Sensor. Although, the coolant seems to be doing well, I do want to check this.

Please keep in mind that this car is a very nice running car, even with this issue. The engine runs smooth, great power, never dies. The engine is very clean, and not just from the dealer likely spraying it before putting it on the lot. I've had it over a year, and it's just as clean. It does not use up transmission fluid, checking the oil every 3 months shows that I STILL don't have to add any. No fluid leaks of any kind.
The only known problems, other than this O2 thing, is that it needs new brake shoes on the back, and a new strut on the front. Very unrelated.

So. Does anyone have any ideas of what could be wrong? What else can I run tests on? If it weren't for the low fuel economy ever since this started, I'd just ignore it. ANY AND ALL suggestions are needed and appreciated. If my email is shown, don't hesitate to email me as well. I'll check this forum daily.

Thanks, and take care!

EDIT: I just tested the Coolant Temp Sensor, and it looked fine. If it's working right, I hit the 240 degree F mark, and the cooling fan didn't kick on, yet car showed no signs of overheating. Doesn't seem right. Cooling fan does work, have seen it kick on at times.

And. Then it ran out of gas. Gotta grab a gas can!