Sorry this one is long. I have a '93 yota truck with a 22re in it, and it is running rough at idle and severely bogs down as soon as I start driving it down the road. Around the same thing was happening about six months ago, and it turned out the wires for my oxygen sensor had laid down onto the exhaust and melted together. I re-wired them and it worked fine until now. I just went to a junk yard and got another sensor to try, and it does the same thing. But now I realized that as soon as the engine is warm it starts running at extremely low rpm's (350-400) and wont drive anywhere. It didnt do that last time. I tried running the engine and un-plugging and re plugging the oxygen sensor back in. It runs the same, the only difference is the engine light comes on when it is unplugged. I am stumped. My best guess is the oxygen sensor still, but dont want to dump $100 on a sensor when it isnt bad. Does anyone have any ideas of what else to check? Thanks.

You can test the O2 sensor per the procedure in the Factory Service Manual. Basically hook up an analog volt meter to the OX test connector and then check for about 8 ~0 volt to ~1 volt swings in the meter in a 10 second period with the engine up to temp and running @ 2500 RPM.

Have you retrieved any CODES?

It is not the sensor itself I tried one I know is good an hour or two ago and it was the same. I never got a check engine light until I unplugged the o2 sensor I didnt think the computer had picked anything up. How do you check for codes with this obd 1 set up? I know each manufacturer is different. I have pulled each spark plug and looked at each of them. They all look the same, a little white like running hot maybe. I dont know what else to check maybe fuel pressure? Ill be doing that tomorrow.

How to pull trouble codes:
http://www.4crawler.com/4x4/CheapTricks/index.shtml#TimingCheckConnector

Thanks. I pulled the codes, which were 21 and 41 which are oxygen sensor and throttle position sensor. Those two only showed up because I unplugged both of them to see if it made a difference in the way it ran, which it didnt. I know for sure it is running very lean right now, which wouldnt point to an oxygen sensor or throttle position sensor, as when either one blows it is supposed to be burning rich if anything (correct me if in wrong). Im pretty sure the fail-safe for all of the E.F.I. sensors is to run rich if it goes bad since it is safer to run rich than lean. The one thing I can think of is the fuel pressure regulator. If it gets no or low vacuum it is supposed to run rich, but I wonder what would happen if the diaphram of the regulator blew out? Other than that I am stumped. Any ideas?

If the pressure regulator went out all together, you would get the full pump pressure at the injectors, maybe 50psi or so and then run really really rich, or you would have gas squirting out all over the regulator if the diaphram blew out. Easy to see if the FPR is working by alternately hooking the vacuum line up to the intake manifold or leave it open to the air and see what the engine idle does. With no vacuum, the engine should load up and run rough until you hit 2500RPM or so. You can test the O2 sensor per the steps in the Factory Service Manual, same with the TPS.

Clear the old codes (disconnect battery), and see if any new codes get generated.

No, no new codes. I tested the A.F.M., but I am not quite sure if I was doing the last step correctly. In the last step it says the resistance between terminal E2 and Vs is supposed to be 20-400 or 20-1000 ohms fully closed, fully closed to fully open. I am not sure if that means when fully closed it is supposed to be between 20 and 400 and when fully open it is supposed to be 20-1000. Or if it is supposed to be somewhere between 20 and 1000 for the entire swing of the door until fully open. At fully closed I am reading in the 180's (within range). At fully open I am reading in the high 200's but anywhere in-between I am reading 1.1k ohms and above. Which is correct?

Can anyone clarify for me what the resistance is supposed to be doing during the swing of the door?