So i bought this car last weekend and there were no problems with it. it sat for a few days while it waited to get registered. I drove it a little the day it got registered and the next day it started having problems. It drives great with 172,xxx miles on it but it has a really slow rough idle. it idles between 200 and 250 rpm and the interior and dash lights flicker and it shakes. it has stalled out twice at red lights but i had no problem starting it up again. PLEASE HELP. I have no idea whats wrong with it but I have very little money to spend on fixing it. All input is appreciated  im feeling like this right now.

start with plugs & wires... a tight PIA job but results may be just right... (assuming you're throwing no codes)

clean or replace PCV & clean the throttle body (get some Seafoam Deep Creep)

check vacuum hoses, when old they tend to crack, which may cause the engine vacuum to be irregular which may trigger the stalling. There's a hose that comes from the engine connected to the intake, it's about 7/8 of an inch in diameter, when loose or cracked it may cause the engine to stall, rough idle, or even shut off. Check oil, belts, pulleys, and tensioners, also check timming belt and tensioners, if doing the timming belt don't forget to replace the water pump. Put some Fuel Injector Cleaner in the tank and see if it betters the idle; changing fuel filter may be also a good idea, poor fuel pressure and dirty filter may lead to faulty injectors.

It also may help to know that occasionally when sitting there with the rough idle, it may jump back up to about 750-1000 rpm for a second then drop back down

i would start with the electrical connections, battery and alternator.

maybe a ground wire.

a low idle will not cause the lights to flicker, if the battery is good.

but any of the three above can cause engine running issues.

but my guess would be alternator.

 

check the battery connections for clean and tight.

check the alt connection.

get a local parts store to check you system.

 

it wouldn't hurt to look for a vac leak,

that is the most common cause of an idle issue.

but i don't think that would cause the lights to flicker.

 

good luck.

You may want to replace the Coolant Temperature Sensor. I has a similar problems a few years back where the idle would stay at 1200 RPM or drop down to 500-600 RPM because the sensor was not working. Once repaced it correctly went right back to 750 RPM at warm idle.

Yeah it very well may be an issue with the vacuum hose, because in the morning when the engine is cold and I'm in the driveway the idle is fine but when the engine warms up the idle starts being irregular. The hose would make sense as the crack mug be small until the hose warms up too and then the crack expands.