I was out in the RX tonight and noticed something weird. When the car was warmed up and idling I stepped on the brake to put it in reverse and noticed the rpms drop a bit. When I let off the brake the rpms went back up. I tried it on diffrent occasions and noticed it several times. When I came back from my ride I pulled in the driveway and noticed it drop like 300 rpms when I pressed the brake. I let off and it idled fine. Could this be a vacuum leak of some sort?

 

could have a small vac leak in the booster. check the booster with a vac pump and see if it holds vacuum.

 

I am not sure if this is relayed, but there is a check valve on the vacuum line to the brake boost. Might want to check that too. Good luck.

 

I have had this exact issue for years. I thought it was all related to electrical so I put in a FD Alt. Car still has the same problem. I have since ordered new Vacuum Hoses but have yet to install them. Thanks for the help guys!

 

Thanks as well, too. I will have to get a diagram and get my friend to help me look into this.