95' de Ville 4.9L
 

I helped my son work on his de Ville today, just a standard tune-up. We changed the plugs (the first four on the radiator side) and replaced the wires as well. We changed the distributor cap and rotor and reused the coil. We ran out of time for today and was going to replace the firewall side plugs tomorrow. When we test fired the car it started right up and the motor runs fine...now the problem. As soon as we step on the brake the motor stumbles and stalls, like there is a short or something electrical going wrong. We were careful when dismantling things trying to avoid any problems. Where did we go wrong? The motor freely reves up without issue but as soon as the brake pedal is depressed to put into gear the thing stalls. Now what? Thanks for your help...

Sounds like a vacuum leak was introduced. Check all vacuum hoses. When brake is stepped on it takes more vacuum out of motor and if there is a hose off or cracked, it would act like that.

Thank you for your quick reply...I purchased some choke and carb cleaner to check with a vacuum leak. While running I could not detect any leaking but I did hear a buzzing sound coming from beneath the cover to the coil atop the D/ cap. When I pulled the cover off and started the car I can easily see where there was arching coming from both leads the red and the white?? It also looked like there had been some previous events along the edges of the metal surrounding the coil that look like hot spots or something but the arching where the lead come out of the coil and the tach/bat plug ins are connected any thoughts?

Sounds like a vacuum leak was introduced. Check all vacuum hoses. When brake is stepped on it takes more vacuum out of motor and if there is a hose off or cracked, it would act like that.