Hi guys, a problem has recently come to my attention, when I press the brakes the car starts to idle poorly, it will sit at 900 then slowly drop to 700~800 then come back up again suddenly. This effect is worse with the headlights on, with headlights on and brakes pressed the revs go down to around 600 then come up again, it will happen every 10 seconds. It seems like an electrical issue, does anyone have a clue?
Does it act the same whether brakes are only lightly pressed or heavy? If so then likely electrical. If it is more pronounced when heavy then possibly an issue with the master cylinder booster.
The grouding point or is it on its way out? Acts the same wether the brakes or heavily or lightly pressed, good thing to know but thanks
If the rpm is dropping with increased electrical load it is likely that your alternator is failing. There is a procedure for alternator testing at the bottom of THIS ARTICLE - I need to redo the pictures but you get the idea...
I can't picture how the brake lights can put a big enough load on the alternator to drop the engine revs without blowing the fuse for the brake light circuit.
