Completely Stumped

[Scampbe5]

My 99 es300 has 230,000 miles on it. It has been out of capacity for almost a month now. I've been getting acceleration problems: I have no power when starting up a hill in first gear, I would turn onto a road from a driveway or parking lot and hit the gas for several seconds while it did not respond (except for a few barely audible clicks), then suddenly it would shoot forward. After I get the initial acceleration I need, it continues to accelerate intermittently in all gears. I am getting super-high RPM's (about 4,000 at 65mph) and pretty low temperatures (after 30 minutes of driving the temp reading will be several notches below the middle line). The problem goes away when I unplug the battery terminal (thereby resetting the computer), then shows up again after five minutes or so of driving. The OBD-II codes I was getting were for the air/fuel ratio (o2) sensors, which I replaced, and the knock sensors, which I also replaced, neither of which fixed the problem. I was also getting a code for "engine is running too lean". Took it to a mechanic, who insisted it was the catalytic converter, and he replaced it to no avail. He also replaced the battery (because what's another $100...?) for me. I also replaced the gas cap, the throttle position sensor and the thermostat and tested the MAFS against an identical one, none of which fixed the problem.

I'm running out of ideas (and funds), but I'm pretty sure it's down to an electronics problem. It wouldn't be the coils or sparkplugs, would it? Should I start looking into the ECU? Suggestions are greatly appreciated.

[1990LS400]

It sounds like the last thing you need is more speculation on the cause of the problem. Is there a Lexus or Toyota dealer nearby? The 99 Lexus ES300 and Toyota Camry V6 are vitually identical mechanically. A Toyota dealer mechanic would likely be cheaper than a Lexus dealer mechanic. Both should have access to detailed diagnostic procedures for your problem.