1997 Neon brakes problem

Good morning,

2 days ago I started my car, let'er warm up completely and started off to work. The pedal was VERY stiff; it took almost a block to completely stop the car. Yesterday I took it to the shop - they put on new pads, turned the rotors and replaced the fluid in the entire system. Worked great last night.
Now this morning it started again, but only for the first 5 or so stops then was normal until I got to work 28 miles away (pulling in my 'slot' it got stiff again). May sound pretty dumb, but would the cold weather have anything to do with it? The brakes were fine up until it got into the single digits for a low with wind chills below 0 at night. Or could it be the master cylinder or lines? This is the symptom of a vacuum leak, or a failure of the power booster. The other brake work you just received may have been needed but it doesn't address the problem of the stiff pedal. You need to have the vacuum checked and possibly the booster replaced.

I should remind you that the car is very unsafe to drive as-is. Thanks, Steve. Not what I wanted to hear, but when it is when it involves car trouble

By power booster do you mean master cylinder or the much-more-expensive-to-replace booster on the firewall? Check the one way valve in the vacuum line going to booster. If it has condensation in it, it may freeze up on cold days and operate properly after engine warms up under the hood. It is a cheap part if it fixes it. Yeah, the check valve is more likely to malfunction than the booster is to fail. Let's hope it's only that. Thanks, guys. I'll have that looked at first.