89 IROC idle problems

I have an '89 IROC (305 TPI) with a couple idling problems. It's bone stock except for K&N filter and Flowmaster cat-back. The fuel pump/filter is new, injectors cleaned recently, just tuned up with
plugs, wires, cap/rotor, timing checked, etc. at local shop. After the tune up it starts and generally runs better, except I still have a couple idle problems that've cropped recently (and no check engine light).
1. Sometimes, but not always... idle seems WAY too high when started cold and won't back down even after running for some time and warmed up. This doesn't always happen.
2. When warmed up, in drive and stopped (eg. at stop light) the rpm starts getting a bit erratic and engine starts missing to the point where I'm afraid it's going to stall out. It does a very odd 'lurching' that I've never felt in a car before. Putting it in park helps a bit, but still misses pretty bad.
Thanks in advance.

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