Brakes seem to work when engine is not running, when engine runs, breaks do not work

Damaged brake switch or chafed wiring.

first problem indicates that the temp gauge wire is shorting out on the engine or the temp sender unit is faulty
second problem if you have your foot on the brake when the gear selection is made and the engine runs rough , but runs good when you take your foot off the brake , then that indicates a problem brake booster with a severe vacuum leak

Check for vacuum line leak by removing the hose from the booster and plugging off. If the engine settles down and runs ok then there is a problem in the booster controls or diaphragm. Replace the booster if that is the case. Hard brakes is the result of no vacuum assist when you put the brakes on and the noise is air escaping into the manifold through the hole and making the engine run rough.

your brake lines have a leak somewhere

Brakes and engine are totaly diferent systems. Do you have brakes when engine is off? If so the only conection between engine and brakes could be vacume which is created by the engine stored in the chamber at the master cylinder to assist with brakes but does not overide personal brake presure only help increase braking. If trully you have less breaking preasure with the engine running then check the vacume line at the master cylinder to see if there is a vacume or maybe preasure?

look for the idle air bypass valve it sounds like it is stuck open leaving the engine idle at too high of an rpm, that would explian the hard braking because it cant build any vacum for the brake booster to work.

abs stands for anti breaking system its something strting to go wrong with your brakes it throws that code until you fix the problem could be serious could be low break fluid find a honest mechanic shop most of them will tell you what it means free they can pull the abs code that tells them what it is good luck

You have an air leak from the brake servo.Block the hose at the servo and see does it run better,if it does then its the servo.Also check the vaccuum hoses off the main servo hose.You have no vaccuum in your servo and thats why the brakes are solid.

sounds like brake booster not working
check vacuum hose that goes to booster is ok and not leaking
engine off
pump up brake pedal several times
hold brake pedal down
start engine
pedal should sink down approx half to 3/4 way down indicating booster is working
if pedal doesnt go down when engine is running booster has leak or no vacuum supply from engine which requires great pedal effort to try and get vehicle to stop.

You need to see if you have fluid in the master cylinder's resivoir.. low fluid or no fluid could be a low break pads or out of adjustment problem ....if fluid is low add dot3 break fluid..and step on the pedal a few times...if the level seems to hold it could be out of adjustment or low pads . If the fluid leaks out then you have a leak and must attempt to find it yourself or with a mechanic. It is possible you may have air traped in the system and it may need to be bled out by a mechanic. I say a mechanic because this is a crittical safety system needed to stop the car !! If you are not sure of how to repair a leaking brake line or caliper or master cylinder leave it to a pro . At least you may be able to find out what is leaking with this help .