When I put my rear defrost on in the mornings just after starting the car the rpm’s drop by like 2-300.
Ground issue?
Or just lack of adequate power on initial start-up or something?
Could be a bad battery, but more likely it’s a tired alternator. It just can’t provide the current on demand that the rear defroster requires. I assume that the rear defroster works though?
Yes everything works fine. I was just curious as to whether this was a sign of something starting to go or not. The alternator idea makes sense, she is pretty old. Tks man.
Any other accessories causing this? When you turn on headlights etc do you get the same kind of thing? Does your car’s RPM’s sometimes drop down as well when clutch & brake sudden stopping?
Or is it really solely the defroster?
Let me know whatcha find out man. 
Well, after letting the car warm-up, when I push the brake, the RPM’s drop similarly. Other than that, nothing else seems to reproduce the same results.
My car does this too. I wouldn’t worry about it since mine has been doing it for 2 years.
good to know…giddy-up 8)
Try putting on your air conditioning and see if it does it. when there is an electrical load on the engine the fast idle valve should open to keep the rpm’s up. The air conditioning turn’s the fast idle on aswell because of the rotating draw on the belt which would slow the RPM’s and cause rough idle. What does your RPM drop too?
That’s not going to work…my A/C doesn’t work. I believe it’s disconnected too, so pressing the button on the dash does nothing.
It will drop about 200-300 RPM when I turn it on. It seems to not be so obvious when the car is warmed up however. Just when I first start the car in the morning and put the rear defrost on. The drop in RPM when applying the brakes seems to happen all the time if the car is park, but I assume that that is a slushbox thing?