So I’m new to this forum, and also new to the car world, but I was hoping someone could shed some light on what my car’s issues might be caused by and/or the solution. I have a 2000 Mitsubishi Lancer Gli, I bought it about a year ago and have had this issue since the beginning but it has slowly gotten worse over time. Whenever I’m idle, it, for a lack of a better term, bounces or chugs. Whenever it does this misfire, I’ve noticed that all the electricals seems to stop or dim (ie the dash lights dim down then go back to normal, same with headlights and I’m assuming tail lights, radio, etc). I had my spark plugs replaced about 2 months ago and that seemed to settle the problem, but not fix it entirely, and within a few weeks it was back to being as bad as it was pre-spark plug replacement. I also had my timing belts replaced (not as an attempt to fix this issue, but it was due) and if anything, that seemed to make it worse. Does anyone have any ideas?
Is the check engine light on? What are the codes if it is? Any other dash lights glaring away? How many miles on the engine? What transmission- auto or manual?
I wouldn’t be surprised if your battery was pretty old and not holding a charge much. You might want to have it tested.
Theres no check engine light, I’m pretty sure every light inside the car is dimming, so all the dash lights, the radio, probably the cab light but I haven’t really noticed that, air con and whatever.
It has 210,000km on it and it’s an auto.
That could be it- I know that my car goes flat really quickly if I leave the lights on, I will have to test it with another battery and see if anything changes
It sounds like the engine is idling too slow, try cleaning the throttle body.
Alternators can’t keep a good charge going to the battery when the engine is at idle. Normal engine idle RPM should be around 750 RPM. Even at that RPM the alternator can’t produce enough power to keep up with a good load on the electrical system. As already stated, the battery is most likely weak and may need to be replaced. Make sure the battery terminals are cleaned with a battery post cleaning brush. Dirty battery connections can cause a charging issue. Along with having the battery tested, you should also have a load test done on the charging system to make sure the charging system is in good shape.
I’ve poorly fit a different, bigger battery and the issue seems to be solved for the most part- there’s still a couple bounces here and there but as for the massive misfires when accelerating from stopped, that’s gone entirely. Thanks guys. 
Hey guys, lol coming onto a year later and my car is still having the same issue. I had fitted another old battery into my car and got little to no improvement, and about 4 months ago I caved and bought a new battery. Still no change. Any ideas?