I started the car up to hear the nice sound And something VERY weird happened. The car drops down to normal idle, then if I hit the brake, it will jump up to 1500rpm just like it does when you FIRST start your car and it is warming up. WTF??? is up with that? heh the brakes should have nothing to do with the idle.

 

ecu adjusting? or you triggered the o2 sensor or some wire.

 

what car? please say 3rd as klown car parts should stay on 3rd gens hehehe

Are you sure the test pipe isnt leaking? any vacuum hoses disconnected? it is strange

 

reset ECU, and secured all 4 14mm bolts then try again...

 

Sounds like your power booster might have a vaccum leak.

 

I was thinking that the ECU is adjusting to you NOT having that additional pressure associated with the cat. Might wanna reset it, like everyone else suggested.

 

3rd gen foo, it wont work on the 4th

I will try the ECU resetting and see how that does. The test pipe is not on right now, just the open y pipe and a missing cat.