My engine wants to stall when I’m at a stop – ever since I had the battery replaced! What happened?
As technology has progressed in automotive design, so have unexpected (to the consumer anyway) side effects. One of the changes that has been implemented is the electronically controlled throttle. For Mazda, most of our vehicles came with this as of 2004. Prior to this, vehicles had a throttle that was directly controlled by the cable attached to the gas pedal. The throttle is essentially a metal tube with a flap that regulates air flow : the flap is closed at idle and opens as the gas pedal is depressed.
One of the normal byproducts of internal combustion engine operation is carbon-rich gasses that recirculate through the engine. These will accumulate throughout the intake (regardless of make,model,year,etc.) and more specifically on the throttle plate. This will slowly cause the throttle plate to stick slightly open, allowing air to flow past when it “shouldn’t”. On the good side, the PCM (powertrain control module – the engine computer which controls fuel, spark and timing) will adapt to this gradual change, typically noticeable after 80,000kms.
This memory is cleared and reset to factory settings any time the battery is disconnected (can also be reset if fault codes are cleared after performing a check-engine light repair). Now the PCM can no longer compensate for the additional air flowing into the engine, causing a lean mixture (too much air , not enough fuel) and results in a poor idle and even stalling.
The fix? Clean the throttle body. It’s slightly more involved than it sounds as it requires the component to be removed from the engine; then the PCM needs to be “retrained”.
Ideally, the throttle should be cleaned periodically – between 50,000 and 80,000kms – to prevent these and other potential issues.