2000 Mazda 626 Idle Problems

It sounds like a fairly simple problem. Your vehicle is of an age where the rubber parts on it are drying out and reaching the end of their life. This is more often the fact with the vacuum lines on the engine. They have a tendency of getting small cracks along the sides of the lines where they attach to the engine and other parts. They can easily be checked by visually looking at them or even taking hols and gently twisting then in one direction. They will not want to turn unless they are cracked and loose. Check the size of the line and length and buy some new lines from the local parts store. If you have more than one cracked line then you may want to replace them all. If you do this do one at a time so you get them on the correct line placements. Another cause could be a bad of plugged PVC valve. They are easily replaced and are on a large vacuums line connected to the valve cover. They can cause a vacuums leak that makes the motor shake when idling due to the vacuum leak. Another cause, but not as likely is the EGR valve which gets plugged up or stuck creating a small vacuum leak that makes the motor shake at low idle. From what you say I would say the ECM (Engine Control Module) is trying to make up for the vacuums leak by increasing the idle speed. The normal for your engine should be somewhere around 800 rpm, but the ECM is reading the O2 sensor and increasing the rpm to compensate for the air/fuel mixture. Good Luck, RAC

It sounds like a vacum leak