94 Mazda MX-3 Surging
 

1994 Mazda MX-3
1.6L 16V DOHC
50,000 miles

Vehicle was parked unused for 9 years under a carport. In 2015, brakes, battery and fuel pump were replaced and vehicle resumed service. Initially, vehicle ran well, but seemed slightly lacking in power. After 6 months, a rough idle was noticed, with the vehicle exhibiting what seemed like an intermittent misfire at idle.

At this point the spark plugs, plug wires and distributor rotor were replaced without a successful resolution to the problem and the misfire grew worse.

Eventually, the Check Engine light started blink codes for the Mass Airflow Sensor and the Throttle Position Sensor. Both were replaced which caused the Check Engine light to stop, but did not have any effect on the idle or lack of power.

Recently the transmission HOLD light began flashing from time to time. This resulted in the Transmission Speed Sensor being replaced, but did not resolve the flashing HOLD light. Transmission fluid was replaced, but still no resolution to the flash of the HOLD light.

Within the last 3 months, an Oxygen Sensor (Inversion) code from the Check Engine light and the engine will not rev past 2400 RPM. At 2400 RPM it will drop RPM’s and then surge back to 2400, drop and surge, drop and surge, until the throttle is released. Sometimes there will be a backfire through the intake. If the throttle is just at 2400, the surge cycle is slow, if the throttle is opened wider, the surge cycle is faster.

O2 sensor replaced, throttle body removed and cleaned, EGR valve tested, checked for vacuum leaks and inspected vacuum hoses, still surging. While the Check Engine light for the Oxygen Sensor (Inversion) has stopped, the codes for the Mass Airflow Sensor (08) and the Throttle Position Sensor (12) have returned.

You may have leaking injectors. It's just a guess of course. Search YouTube to learn how test injectors. Don't throw more parts at it.

did yoy ever figure out the probelm... i have the same exact problem?

I had a 1994 Mazda MX-3 1.6 DOHC 5-speed for many years. Strangely, it needed spark plug wires every 20,000 miles or so, but you wrote that you already replaced them. For your sake, I'm hoping it's something simple. Have you changed the fuel filter? I used to change mine. It's located deep down on the firewall. The clamps are especially hard to reach, but with a set of hook-nose pliers, it can be done.

When resurrecting a car that's been off the road for so many years, it's a good idea to check the fundamental condition of the engine. A leak-down test - as opposed to a simple compression test - will help you identify any problems with compression, such as blown head gaskets, dropped valve seats, etc.