Running 5000 RPMs in neutral when using A/C at high speeds

The Honda dealer and my mechanic have two different opinions, and I need more advice before I go with either repair.
Car: 1999 Civic LX, manual, 150K miles
Two main symptoms:
1.) Sluggish when I first depress the gas pedal. In every gear intermittently, but alsways when I'm in second gear, there is a hestition, then it kicks in. Giving it more gas doesn't help.
2.) When driving high speeds for an hour or more, running the A/C, tt revs as high as 5000 rpms in NEUTRAL. This was fixed when my mechanic cleaned up the throttle body, but it just happened again yesterday. After the car sat for an hour, it started up no problem. No revving in neutral.
The dealer said its the catalytic converter (based on a code reading), but my mechanic said the converter is clean, looks good. My mechanic is suggesting that its something in the throttle body.
Any advice, thoughts, similar experiences?
Thank you!
Sarah
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SET wrote:

You need to quote the CODE number, from the work order. Take a look through the TSB's for your car and see if anything jumps out at you:
http://www.tegger.com/hondafaq/tsb/index.html#list
Do you use injector cleaner now and then? Has the timing belt been replaced recently, and is the coolant reservoir full enough, per the owner's manual?
'Curly'
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