I recently installed a new engine on my 8. When the car is on it struggles to stay on by constantly revving it self up. When i drive the car and come to a complete stop then set it to neutral the car completely shuts down. Help anyone

 

Does it rev up and down between 700 and 1500 rpm's?

 

You may find some clues in Replacement engine stalls at idle? https://www.rx8club.com/series-i-trouble-shooting-95/replacement-engine-stalls-idle-218004/

 

Sounds like it might be your SSV. Is your car throwing a code?
https://www.rx8club.com/showthread.p...hlight=ssv+diy
Check out that link for diagnosis to see if it is the SSV and the DIY. It ended up being the SSV for you right Marie?

 

Hmm, I think they'd already replaced the SSV, then the weird idle/stalling happened when I went to pick it up.

They then did that Mazda cleaning service thing for the injectors and intake and it's idled perfectly ever since

 

I'm glad its running good for you. After I replaced my SSV I have a very small coolant leak somewhere that I have to hunt down.
Unfortunately it is not leaking enough for me to be able to find it at idle. I'm guessing it will be a bigger leak at WOT. But anyways to OP I had the same exact symptoms on my car and I cleaned the SSV and it's perfect now. My theory is that the valve is stuck open at idle causing the A/F to be to high causing it to die out.

 

ok the car does idle between 2 and 1 then dies out and no, its no throwing any codes. uhmm i used the same spark plugs from the previous engine because i had just replaced them but i dont know if that could cause the problem. Could the cat cause it i havent chandged it anyways any help will be appreciated

 

Cat doesn't usually cause that. Cat usually causes high rpm hesitation. You have newer plugs on it but what about the coils? Do you mean it idles fine when ita cold aka the rpms being higher than usually but when it warms up and the rpms drop the car wants to die and you have to constantly give it gas to keep it going?

 

Lol.....that one took a while to figure out way back

 

Yeah that is exactly what it does. When its cold it revs up normal then it loses power and i constantly have to give it gas for it to stay on. I'm sorry i didnt mention but i had recently changed the wires, coils, and plugs on the previous engine so i used them for the new one. I had clean the throttle body and the intake but not the injectors.

 

The fuel harnesses are installed properly, i also replaced the cat and the cyllindroids on the intake manifold. I do know what else to do, not even the dealer knows whats wrong with the car. i need some serious help.