Ok so I go to drive my car today, it starts up fine... keep in mind the symptoms of this problem have happened before then just went away....but they just came back again today..car has 12000 miles on fresh rebuilt engine.

1st problem -

when i rev it the rpms drop down much lower than they should before stabilizing and the car almost wants to stall out alot and i have to gas it to prevent it from stalling out , it will keep on doing this until the car is completely warmed up , and even after that the rpms are still dropping down lower than they should when i come to a stop..and slowly raise back up.

2nd problem -

Lots of backfire on decel under 3500 rpm and downshifts that are hitting 3500 rpm and less.

3rd problem -

Sputtering on low throttle in gear...does it more in lower gears and less in higher gears on the low throttle...(i think it does it less when there is more load ? )

Also will sputter in neutral when i try to get it to hold 1500 rpms, it just wont hold that rpm stable and the idle will surge and car sounds like its sputtering.


Conclusion -

Is this a faulty tps that is coming and going ? Or is this a problem in my cars wiring ??

If its the tps , will replacing it surely fix the problem or would i be guessing it would ?



Also another problem that may not be related but I have question about it -

I sometimes have major loss in braking power, and the brakes seem like they always go to the floor when i am at a light holding them if i hold them down tightly (loss in pressure).

Someone told me if my booster has a leak i should be able to pump the brakes and get brake pressure...Ive recently tried to do that, but i cant even tell if im getting pressure because the car starts stalling out and wanting to die...what could the problem be ? I would think maybe the booster does have a leak in the hose on it because the more i pump it the more the idle drops/surges and makes the car want to stall out.

Someone else said it was probably my master cylinder...but my brake fluid hasnt gone down...and i think the hose to the brake booster from the intake mani may be leaking ...so thats why i think the brake booster is causing the problem.

 

Seems like fixing this (obvious) vacuum leak would be your first step.

 

I'll have to get one from mazda, someone told me they are like 20 bucks and have some kind of valve in them.

I think this may fix the problem with the brakes but it wont fix the other problems im having under load...when youre hitting the brakes there is no load because youre not hitting the gas, at least thats what I would think.

 

The booster line nearest the booster itself does have a one-way check valve integrated into it.
It can replaced with an OEM part or any bit of vac line with a check valve.

Many of your other issues could be related to a vacuum leak.