So here's the background.... My 94 Z28 has had a surging idle problem for the past year or so. After the car got up to operating temperature and came to a complete stop, the tach got shaky, and the engine would rev up on its own. This happened in any gear, including park, but it was a relatively minor intermittent problem. A few weeks ago, the car suddenly had a severe stumbling and hesitation problem when accelerating from a stop. So I took the car to a shop and they changed the stock wires to MSD Super Conductors and put in a new MSD cap and rotor for my stock opti. That completely fixed the hesitation problem... but now the idle surging problem went from minor to severe. I brought the car back to the shop, and they tried swapping the computer as well as the ignition coil, but the revving at idle was still there. Now they're telling me they think it's the distributor (not the cap and rotor) that's causing it, and they need to replace the rest of the unit. Of course I flipped out, and I decided to get out of there and get your opinions on the problem instead. In hindsight, I should've just ordered a jason cromer OEM opti and put it in myself, but now it's too late. Here's a log of about a 4 mile drive with a few stops. You can see where it gets really bad at the end of my drive when in Park around cell 14726. No trouble codes thrown.

I really appreciate any help that you can give, especially because I know it takes time to analyze logs.

Here's the log file

 

maby IAC???

 

From what I've been told, the IAC going up could just be a consequence of the problem rather than the culprit. Thanks for the response.