I have a 1998 Mazda 626 4cyl. I have an idle problem that I believe is due to a vacuum leak. I can hear the leak but cannot determine where it is coming from. When the car is idle, it has a hard time staying at the 800rpm. If I rev it up and let it drop, odd are that it will stall out since it cannot recover to an idle.

When the car is in drive, the problem is less noticeable and when driving, no problems. I have had a “bank 1 too lean” error. I have put in new NDK sparkplugs, cleaned the MAF sensor and replaced the upstream O2 sensor.

Please help! Any suggestions would be greatly appreciated!

Thanks!

 

Here we usually locate air leaks by spraying carburetor cleaner or something like that (sometimes even gas!) onto suspected places and checking whether RPM vary or not. Once the engine’s speed changes it means that there is air leak. Also, according to my experience it happens rather often that broken intake manifold gasket in the reason of false air. So, you may start with spraying your intake gasket. Another possible place could be flexible air pipe between the air filter and the throttle body.

 

I would use something less harsh on the rubber when spraying...carb cleaner and starter fluid will take a toll on old rubber and plastic vacuum lines. Some people do a smoke test to locate vacuum leaks. Gasoline is just a bad idea if you care about your car!! Also check your coolant lines connecting to throttle body and BAC valve. Or vacuum on main brake booster hose (usually a tiny one-way valve inside), and leaks between MAF sensor and throttle body.

 

I had this problem and it was the throttle body gasket. For some reason the aftermarket metal gaskets don't seal properly. I used an oem paper style gasket with non sillicone permatex, and problem solved. Don't use any sillicone products on any air or emissions related parts, as these will ruin your o2 sensors and others as well. Hope that helps.