1987 wont idle
 

PLEASE HELP ME
my mazda 1987 starts fine but wont idle. It has a new computer and leading coil from mazda and a new engine from atkins. when it starts it goes straight to 3000rpms. it sits there for acouble seconds then falls back down. it never stops to idle and then dies. if you give it gas it will keep reving up. if you keep the rpms above 2700 to 3000 it runs good. not great but good. a little back firing and kinda sounds like its off timing. i also jst put a new fuel pump, didnt change anything.
Thanks CHRIS

You probably have a large vacuum leak, and these can sometimes be a bear to find.
1) Check the vacuum hoses for tight fit at each end and possible cracked or broken lines.
2) Gaskets at the UIM and LIM
3) Grommets and O-rings at the injectors can wear out and become brittle over time

Unfortunately, with vacuum leaks there isn't an easy button you can press to fix it