im new to the mustang and car repair world i have a 69 coupe and it just started idling rough not in park or neutral its when i am in drive and i come to a stop. its almost like it is surging and almost dying out.when im actually driving its fine and its ok in park and in neutral.....any suggestions?

 

you can set the curb ildle a little higher.. or you mayjust need a new fuel filter.. If it has gotten gunky recently that could be blocking your fuel flow until reved,, Try them both.. A carb tune, in general could help you out though..

 

you may want to consider a full tune up while you're at it (plugs, wires, cap, rotor, points, condenser, fuel filter, air filter). Money well spent.

 

yah. but for starters try to just increase the idle a bit.
depending on the carb you usually have 1 screw to increase the throttle opening on idle. Maybe that was set too low.
(some people just love the sound of an engine nearly dying)
or maybe the mixture is just far too lean. again depending on the carb they just might be too far closed. If you have one or more mixtures screws open them by a quarter turn.

Most importantly: remember how the crews were set originally. so you don't misadjust.

What else might be a problem is you're saying it's when you are in idle and hit the brakes.
Do you have a servo ? (powerassisted brake). If yes, that might be your problem. -> check all vacuum lines.

as well if you have a brake cleaner, spray it around the carb (not into the carb) while in idle. if idle speed changes you might have a leak somewhere

 

I have the exact same problem with my 67 in line 6. It only happens when the car is in drive or reverse. No power brakes, I just did a full tune up plugs, cap, roter, wires, fuel filter, it has eletronic points. I also took the car to a trans shop to heve the auto trans checked, no problems there. My next try will be carb first ill mess with idle them lean or rich then a rebuild. Keep me posted it is driveing me crazy and I want the problem gone.

 

Vacuum leak!
Spray carb cleaner 'bottoms up' from the base of the carb to each gasket/seam. If the idle suddenly picks up and then dies again - that is the leak.

Tweaking the idle or mixture cures a sysmptom - not the problem!

 

yeah man. i always like having my idle low too. gives it a nice tone rumble. but itll die out and serge if its a bit too low. i have a fealing its just your idle. you cant miss it just take off you air cleaner and find the big screw on the drivers side of the carb. itll have a spring around it. tighten it up to turn up the rpms and down to lower the idle and rpms. hope that helps!

 

I just fixed my rough idle pain in he *** this afternoon. It turned out to be vacume leek like most people here suggusted. Bad PCV! check replace the valve and the line, then set idle. Good luck.