Soft Brakes and Erratic Idle

Evan_Lovell

Hey guys, like the title says I have incredibly soft brakes and my idle will jump up about 500-700 rpm. I've noticed the brakes arent soft when the engine is cold and the idle doesnt jump around when its cold either. I was told that the brakes could be soft because of the idle. But it sounds to me like a bad master cylinder. Any ideas?

bam-bam

Leaking brake booster or possibly just the rubber sealing washer behind the master cylinder. High idle indicates a vacuum leak.

It is possible that a faulty master cylinder is contributing, an extended stroke could expose a crack in the diaphragm.

darktrickster

What Bam-Bam said. Soft brakes indicate a fluid leak in the brake system, either out of it all together (your fluid would be emptying very quickly) or an internal leak (most likely in the master cylinder). They could also be caused by air in the line or a rubber brake line that is failing. (rare, but rubber lines can sometimes balloon out)

As a start, I would recommend bleeding the brakes just to be certain you didn't get air in the system as it's easy and inexpensive. As far as the idle goes, sounds like a vacuum leak or your idle air control valve is having trouble finding the correct idle. That can be caused by low coolant or a dirty IACV. Make sure your coolant is full and search a how to on cleaning the IACV.

Evan_Lovell

The brake fluid is half way between "Min" and "Max" and has been since before this started. Ive had a feeling it was the master cyl but I dont have too much knowledge in the brake department.

Evan_Lovell

I think I found whats causing the idle problem. There is a small crack in the radiator top. This might be a stupid question, but is the black upper piece of the radiator plastic or metal?

darktrickster

It's plastic, and prone to cracking. Especially if you still have the plastic air tube that bolts to it. and if your coolant gets low, your idle will be erratic for sure.