You need to pull the codes from the computer. It is OBD-I so it is very
easy, but on a motor that old these problems could be caused by several
things each. I have no way of knowing what is actually going on from your
motor from where I'm sitting or how well you take care of it, so I'll
mention just a few probable causes.
High Idle: I believe your motor is throttle body fuel injected, so it is
most likely an Idle Air Control valve not seating fully (dirty or broken), a
cracked base gasket on the throttle body letting air in, or a bad coolant
Shaking at Idle: Either a bad or disconnected knock sensor, bad plug(s)
and/or wire(s), bad ignition module, cap, rotor, etc.
Bad Fuel Economy: Take your pick, everything from any one of a dozen
routine maintenance items to something more serious - I have absolutley no
way of knowing.
You are going to need much more help diagnosing these issues by someone in
person than you will ever get over the internet.
Cheers - Jonathan
Jonathan A. Race
Lieutenant, EMS Supervisor
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