Mazda 323 Idling Problems - Unstable RPM

I purchased a Black Mazda 323 (1996 Model) last November. I didn't know much about cars at that time. I took it for a test drive, and it seemed to be in very good condition, so I got it.
After weeks of driving, I now became more familiar with the car, and one thing that I noticed was its RPM was unstable.

Here is what you can see on the Mazda 323 dashboard. Take a look the tachometer or RPM gauge at the left side. Ideally, this shouldn't be fluctuating. At idle, this should be at around 800RPM. If you push the gas pedal, the RPM should increase, but once you remove the pedal pressure, the RPM should move back to its original 'idle' position. If you started at 800RPM prior rev-ing up, expect it to still be at 800RPM when your foot is off the pedal. My Mazda's RPM did not return to where it started. Either it was higher, or it was lower. This is an indicator that you have some problems with your Mass Air Flow Sensor. I didn't know that when I tried checking out this car. So for would-be buyers of second hand cars, watch out for this.

My RPM issues was at its peak when I noticed that the engine would turn off when I changed gears, usually in the lower ones. Let's say I had my gear set to 3rd gear, and I needed to slow down and so I had to set it to 2nd gear. As soon as I shifted the gears, the RPM would go very low, to a point very near zero, until the engine would stop. Good thing my car did not have starting problems. Whenever it happened, I would just restart my car. But you could imagine all the hassle it was giving me.

I did a Google search on "unstable RPM". To my surprise, there it was... IDLING STABILITY was a common Mazda 323 problem. There are a couple of forums which discuss these. They might even offer better solutions. I just would like to share what I did to solve this issue.

The Mass Air Flow Sensor is located in under your Mazda's hood, just in between the air intake hose and the air filter casing. You may notice that there are wire connectors attached to this. This is one of the many sensors your engine uses to achieve optimum performance. Its funtion is to send information to the Engine Control Unit (ECU) regarding the amount of air mass entering the engine.

I had a mechanic check my car and his first reaction was that the sensor needed to be replaced. I asked him how much it would cost. He told me it was around P3,000. If it was true, then it's a quite expensive part, so I decided to see if we could do anything else. The mechanic tried moving the air filter casing, and he noticed that the RPM fluctuated by doing that. That should not happen. With our new observation, we both agreed that there was something loose. Next, he pushed on the wire connectors in the Mass Air Flow Sensor and asked me to push on the gas pedal and check the RPM. The result? Even after pushing the pedal, the RPM now settles back at its starting value. Sucess! We fixed it.

So it seemed the connector was just loose. I drove the car for a week with no problems. But soon after that, my RPM woes were back. My car'r RPM was fluctuating again. I needed to find a more permanent fix.

I was convinced there was nothing wrong with the sensor. If there was, pushing the wire connector wouldn't have lead to a significant improvement in the idling RPM stability. So one day, when I got home after driving, I detached the connector and cleaned the metal electrodes. I sprayed them with a good quality contact cleaner. I got back to the driver's seat, rev-ed up the gas and check the RPM again. COOL! No more of the unstable RPM's!

My final conclusion: the dirt in the metal electrodes of the Mass Air Flow sensor was interfering with the quality of the electrical signals coming out of the it, and it was causing errors. The ECU was getting the wrong information. If you're a Mazda 323 owner, and you're having idling problems, it might be worth doing what I did. It's going to save you some cash. But again, the engine is a complex system, and your RPM can be affected by a lot of other parts not working well. If doing this does not work for you, trying checking other parts.