1996 SL ENGINE RACING PROBLEM

My '96 SL single cam has 185K on the clock, and has been running fine.
A few weeks ago I changed the oil and hosed off the motor with a
garden hose. Then the "Service Engine" light came on, but it was
running fine. A few days later it went off, and my buddy at work
hooked up his code readed and said it had a EGR related code in the
memory.
I drove it a couple of weeks, and light stayed off. It wouldn't start
the other day, and wiggling the battery terminals got it to start, so
I drove it home and cleaned the terminals, which really didn't look
bad at all, but I polished them bright with a wire wheel.

The next time I drove it after the terminal cleaning, the engine had a
high idle, and would race up to 3000 RPM when I would clutch it
between gears. the idle would eventully settle down to 750 RPM.
Drove it to work today, and it still would race up between gears,
almost like I wasn't letting off the gas pedal when shifting. When I
would put it in neutral coasting up to a stop, the engine would be at
2000 RPM, then slowly drop to a 750 RPM idle. No check engine light
is coming on at this time.

What could be causing this?