Mazda 6 rpm

Roversfc

I have an 07 Mazda 6 1.8 petrol and ever since I got a new battery fitted the rpms are jumping up and down when slowing down, stopping at traffic lights or coasting, they go so low that the car sometimes conks. Everything else is fine there's no funny noises the car drives perfectly otherwise, I went back to the place that fitted the battery as I thought there might be a loose connection or something but they looked at it and said it's all connected correctly. Any ideas?

Atlantic Dawn

How long ago was the new battery fitted, days ago and mileage?
Do you know if the battery was fully charged when you received it?
My guess could be if it's relatively recently as in this week with say 50 miles or less done in the car that the battery may not have been fully charged and what's happening now is the alternator is labouring to charge it while the car is idle.

Roversfc

Thanks for the reply, it's a brand new battery I got it fitted about a week ago there's 100,000 miles on the clock, haven't even done 20 miles since I got the new battery in il bring it for a good long drive now today and see if that helps, thanks

muckwarrior

The ECU would have been reset and is now in the process of relearning. A couple more drives and it should return to normal.

oknepop

To add to muckwarrior's post above, I had the same issue after getting a new battery and it didn't go away for a while. Reprogramming the ECU fixed this, and there's a manual way of doing this pretty quickly. The way you do this is you disconnect the battery, then turn the key and push on the brake pedal a few times to drain the electronics of any residual charge, and wait for about 5-10 mins for good measure before reconnecting the battery.

After you reconnect the battery, turn on the engine, making sure none of the electronic accessories are running (i.e. internal lights, radio, fan, etc.). Make sure they're all off - and just let the car idle for about 25 mins. This will reprogram the ECU and will stop your car from cutting out. It takes about 40 engine on-off cycles for the ECU to fully reprogram itself, but this first step should fix any uneven RPM/cutting out issues.

You may also lose the automatic window open/close feature on the electric windows after disconnecting the battery. Re-enabling this is pretty straight forward - have a look on google for a how to.

Roversfc

oknepop wrote: »

To add to muckwarrior's post above, I had the same issue after getting a new battery and it didn't go away for a while. Reprogramming the ECU fixed this, and there's a manual way of doing this pretty quickly. The way you do this is you disconnect the battery, then turn the key and push on the brake pedal a few times to drain the electronics of any residual charge, and wait for about 5-10 mins for good measure before reconnecting the battery.

After you reconnect the battery, turn on the engine, making sure none of the electronic accessories are running (i.e. internal lights, radio, fan, etc.). Make sure they're all off - and just let the car idle for about 25 mins. This will reprogram the ECU and will stop your car from cutting out. It takes about 40 engine on-off cycles for the ECU to fully reprogram itself, but this first step should fix any uneven RPM/cutting out issues.

You may also lose the automatic window open/close feature on the electric windows after disconnecting the battery. Re-enabling this is pretty straight forward - have a look on google for a how to.

Thanks I'm going to give this a try now, I'm just back home I brought the car for a long spin and dosent seem to be any better and it cut out twice.
After I disconnect the battery do I turn the key as if I'm trying to turn the engine on or just one or two clicks? Thanks

oknepop

Just to the second click where all the electrics and fan etc usually turn on. Pump the brakes a few times and let it sit a while before reconnecting the battery.

After that, reconnect the battery and turn the car on and let it idle - no other input required from you for about a half hour, the car will do its own thing! Again, just make sure everything electrical is off so there's no additonal drain on the engine.

After the time is up, turn the car off competely, take out the key, and next time you turn it on you should be good to go.

Roversfc

oknepop wrote: »

Just to the second click where all the electrics and fan etc usually turn on. Pump the brakes a few times and let it sit a while before reconnecting the battery.

After that, reconnect the battery and turn the car on and let it idle - no other input required from you for about a half hour, the car will do its own thing! Again, just make sure everything electrical is off so there's no additonal drain on the engine.

After the time is up, turn the car off competely, take out the key, and next time you turn it on you should be good to go.

Just a quick update. I done what you said earlier just back now from bringing it for a spin and it seems to have completely solved the problem, revs weren't jumping at all everything was back to normal. Thanks for your help.