I've got a RENIX cherokee that sat out in the open for several years. Turns over, idles fine for about thirty seconds then drops to 300-400 (estimated, I have no tach yet) RPM... Enough for it to die on its own, if I don't keep my foot on the pedal just a little. It's died several times once I let off. What do I do? I'm about to clean the IAC and check out the TPS, is there anything else I should do? I know there's some tricks to do with the computer using a DMM but it's been a while.

I'd start with the obvious stuff first: new fuel filter, good gas, new plugs, distributor cap wires etc unless you know that this has been all replaced lately. All the typical "tune-up" stuff.

Next I would read through all of Cruiser's RENIX tips and see what you're capable of doing yourself with your own voltmeter. Check readings of TPS (throttle position sensor), sensor grounds etc.

If you've got a RENIX jeep that runs at all (even poorly) you're way ahead of the game. The worst situation is the "no start" condition.

Check the basics - plugs, cap, rotor. Might be gunked up fuel, too. Sitting is the worst thing for a fuel system.

EDIT: Oops. Cross posted. GMC nailed it.

id drain the old gas out and put new gas in as well. My jeep sat for 2 months more with brand new gas because i thought i could get it on the road but nope and i went to start it with a dead fuel pump im like really this pump is not even a year old?!!! so took it all apart AGAIN and the new pump was all corroded and the motor would NOT move. So had to yet again get another pump and now it works fine. Tho may need to tune up and clean my engine up alot after what its been through.