Hey guys I have a 85 f150 300i6 4 speed manual and lately when I press the brakes it starts bogging out it'll go from a grand to around 500 rpms and that's if it doesn't stall out. I did change the master cylinder not long ago but I can't recall if the problem occurred before that. I was told it could be a vacuum leak or the brake booster but im not sure and my brakes work fine. Any help would be greatly appreciated!

 

for the life of me i cant recall what the part was called... however on the back side of the carburetor there is an electric part that extends out in order to hold the throttle open a little bit more, a little bit longer after you completely remove your foot from the gas in order to apply the brakes. this was most common on A/C equipped vehicles because they could tend to bog down with the extra resistance provided by the compressor.

so, that part could really be the only other option besides a vacuum leak, unless you have been fiddling with idle mixture screw. with how old the truck is, it may just be a smart idea to buy a bunch of hose and replace it all (it's pretty cheap)

 

That actually makes perfect sense because that solenoid on my carb seized up and was cause my truck to rev at over 2 grand so I had to take it off. Thank you for the help.

 

Also I believe that part is called an idle speed control motor if I'm not mistaken they run for about $80.00 which is probably why I haven't replaced it I didn't think i needed it but stalling out at atop signs isn't how I wanna spend my days lol

 

glad i could help!