Hello I am new to the rotary club I got a 1986 Mazda Rx-7 (2nd gen fc 13b N/A) and wanted to ask you guys some questions please let me know what the problem could be, I have adjusted the idler valve screw to tune it so the RPMS can be at 750-900 and I get it and then I wake up the next morning and it’s completely out of whack anybody know what it could be? Last owner said it was a vacuum leak but I wanted to get your opinion.

 

A vacuum leak is a good place to start. Sometimes small holes in the old rubber lines can change with the temperature of your engine bay. Other seals are known to dry up and crack as well.

Checking for vac leaks is usually the first thing to check, so long as it's just idle issues. Also, check the manual for information on how to set the idle. There is a jumper that grounds an ecu pin so it knows you're setting the idle. If you just keep changing the idle screw without that step, the ecu will try to compensate against the adjustment.