I am getting a -10psi idle @ 600rpm. I just changed the plugs and wires. The heat range on the NGK plugs are 9, but my car is stock. Could this be the reason why it idle so low, the plugs are too cold.

 

Might be time for a compression test.

 

Any particular reason you put all trailing plugs in? If your car is stock you should still be running 7's and 9's. I would switch back to normal. If the problem persists, turn the idle up a tad. Oh, and vacuum is measure in mm/hg not psi.

 

An idle of 600RPM would give you -10mmHg rather than the normal -15mmHg and 750RPM. If your stock, use the stock plugs as has been said by Lost Time.

 

Who sells the 7's? I could only find the 9's. The Numbers are simply the heat ranges of the plug right? I was told it would be ok to be running all 9's from a rotary mech. here in Houston. So its to cold? The shop manual said to put one 6, one 7, one 8, and one 9. WHich one should I do?

 

7's leading, 9's trailing. Check with the RX7 store, they probably carry them.