SES light when braking

[Slade001]

'90 K5 350 TBI

When I step on the brakes my SES light comes on and the engine idle decreases almost tot the point of stalling. As soon as I let off the brake, everything is good. Truck idles rough, but stays running. Have done a "tune up"...new AC Delco plugs, new wires, cap, rotor the works. I am getting ready to do a TBI rebuild, replace the injectors (AC Delco's) and replace the fuel filter. Any other items that could be causing this? Or any other recommendations?

 

[496truck]

Add replacing the brake booster to that list. Problems like you describe that would be the forst place I look. Could also be anything vacuum related so check all that stuff (vac hoses/lines/leaks/etc). Typically when the booster fails you will get an idle jump but not a stalling condition. Unless the master is leaking into the booster and the engine is sucking brake fluid when you step on the pedal. Unlikely, but it has happened.

There are ways to check the booster operation before you go replacing it. Pull the vacuum hose off of it and check for fluid. If no fluid take some vice grips or hose crimpers and pinch off the vac hose to the booster then step on the brakes and see if the problem still exists. BE ADVISED you will have manual brakes without vacuum assist so do this in park or at VERY low speed in a safe open area.

I had erratic idle and idle jumps when on the brakes as well as a "whoosh" sound when stepping on the pedal. Lived with it for a year but what cinched it for me was when I was sitting in traffic one day, let up off the brakes and start to go and had to get right back on them all within 1 to 1.5 seconds and the pedal was hard as a rock (no vac assist) and could hardly get the truck to stop, almost hit the car in front of me. Replaced it that weekend.

 

[blazinzuk]

Yah I would say vacuum issue in the booster somewhere.