1991 geo metro rough idle

relay stuck ,called park relay or as in all electrics
bad wiring
bad control switch to the relay

old post;

the metro works just like the sidekick, less 1 cylinder.
does engine reach 180F coolant temperature and hold?
2 causes, and 8 ways to fail.
http://www.fixkick.com/AirCond/heater.html

The torque converter may be shot.

The main Transmission fluid pump may be shot.

The electricals to the solenoids may be disconnected or relays maight not be functioning.

Look for drips of oil and listen for strange sounds coming from it.

I would start by hooking up a vacume gage, if it reads low check for cracked or broken lines.

try heavier wt oil, check oil pump pressure, replace oil pump if needed

dunno if it'll fix it- but check your pcv valve - 5$ for a new one - also check your egr valve- should be able to move depress it with your finger- if not, carb cleaner is safe to use to clean it up- remove it and clean it. this should help the idle

Try this
Here are the most common causes of surges, stalls at stops, low erratic idle speed, rough idle and engine hesitation, it is in most cases the idle speed control air-bypass valve and or throttle valve and upper intake, these area's get full of gunk and combustion residue over the miles and cause idle issues (stalls, low idle) like yours, Get a can of intake cleaner from any local parts store, not carb spray, intake cleaner, it is made by a company called CRC, remove the air intake hose to the engine, hold the idle high so the engine won't stall, then spray the can of cleaner into the intake while keeping the engine running, use at least 1/2 the can, shut down the engine and disconnect the battery for 5 minutes, then restart and complete a number of mixed driving cycles, town, freeway, stop and go etc., after a few days the problem will go away as the system will relearn to the clean intake.

Could possible be a bad or stuck vaccum advantace mechanism. Check for operation.

i would say you jumped timing your belt moved a notch

ALLDATA.COM IS A GOOD SOURCE OF INFO FOR THE DIY, YOU WILL NEED A GOOD COIL SPRING COMPRESSOR, BE VERY CAREFUL, IF THE SPRING LETS LOOSE BECAUSE YOU USED THE SPRING COMPRESSOR INCORRECTLY IT CAN REALLY RUIN YOUR DAY AND SEND YOU TO THE HOSPITAL.