I have a 1995 Mitsubishi Galant s it's sitting idle after warming up is about 500-600 rpm's what should it be?The reason I ask is as soon as I put a load on ie. Turning the heater on with the light on already the lites dim. It also happens when driving down the road and I come to a lite and have to break, the rpm's drop and the lites dim. Now when I give it some gas and keep it at 1000-1200 rpm's and add a load it seem's ok. The lites don't dim. I think I have a very low idle when sitting. Battery and altinator have been checked and are OK. So what is the desired idle?