1990 buick lesabre help!!

[ezyR1deR]

3.8 140,000 miles. runs great...

the engine powers down when i brake... the speedometer will bounce from say 55 to 25 then back up to about 53 when i lightly or roughly apply the brake, it is really strange. the service engine/temp light also come an simoltaneously as the engine looses power and the speedo needle drops dramaticalyl then rises back up and the car gets power back. the car does get power back after after the half second needle/engine/temp light twitch.. but its doing this alot lately.. what's the problem

may be soemthing to do with ethe electrical system because when the car idles and i turn the lights on it stalls out...

[Smith1000]

I would look for loose electrical connections at the battery, grounds, etc. Are the terminals good and clean with tight connections? Check to make sure the alternator connections are clean and snug.

Might check the alternator output with a voltmeter and see what kind of voltage it is putting out. Check it at the battery when idling. Then, turn on the radio, heater, some other electrical stuff and see how the load on it changes it. A battery shop would check it for free.

[richtazz]

Welcome to AF

If your car has the double stacked positive battery cables, that is most likely your issue. It's a common issue with that design. The cables work their way loose and get corroded between. Don't overtighten them though, as you could pull the side post out of the battery.