You're on the right track with filters and fluids.

If you're new to the '87 or the 124 in general, search "Trap-Ox" and be sure you don't still have one. Your rough idle could be the OVP relay if you have an ABS light and dead tachometer also, what's the idle RPM?

Easiest is to put a BB in the EGR vacuum line, disables it. Still there but does nothing.

Rusty fuel cap means that there was condensation, not necessarily a bad tank. Watch your fuel filters for a tank full or so, if you find that you can't develop full power after a half tank or so, you're plugging fuel filters. Use a good biocide in the fuel and a cleaner (Biobor and RedLine are my favorites) for a tank or two and see if it clears up, might need a couple of spare filters and if you're going on any trips, take a quart of cheap ATF to prime the fuel filter or you might run out of battery before priming the engine.

Next look into suspension bushings, common ones on the rear of your car are the "thrust arm" bushings, rear subframe bushings, and lower wheel carrier bushing (the one that connects the wheel carrier to the control arm in the rear). When some or all of these are bad you will get some squirrelly behavior especially when going on/off the accelerator.

Good luck and welcome to the 124 club.

__________________

Gone to the dark side

- Jeff