Unstable Idling Mazda 3

My car exhibits unstable idling at traffic lights and stop lights after running for about 20-25 minutes. I found a TSB for Mazda 3’s that states this is due to carbon deposits. Is it best to get a fuel injection service done?

What year and mileage?

A fuel injection service may help if they are faulty, if there is a problem in that area you should be getting a CEL and codes.

You might want to replace (properly gapped) spark plugs and check for spark jumping.
After dark, with the engine idling and the trans in PARK and the parking brake fully applied, pop the hood and look for a spark jump along all the plug wiring.

When was the last service done?

Last fuel filter change?

It’s a 2007, with 66K.

I’m not getting a CEL, but do have a CEL for a malfunctioned leak detection pump. But, I don’t think this is related. The CEL is 2404, but is a costly replacement. The TSB says there isn’t anything wrong the pump, so I haven’t replaced it yet.

I’ll try checking the spark plugs at night.

My last service was done around 55,000. Mostly fluid exchanges…I haven’t had new spark plugs replaced, but the engine seems to be starting OK.

The last fuel filter change had to of been sometime ago. I’m not even sure. Maybe it’s time to replace these? I’m always hesitant in using the dealer because the costs for the 30K, 60K, services seem excessive. I try and bring my car into the closest auto shop that seem legit.

That’s what I get for ‘assuming’.

I had your vehicle pegged older and with much higher mileage.

As I don’t have a codebook for other vehicles other than my own, I am unable to pursue youe2404 code which you said referred to a ‘malfunctioned leak detection pump’.?

I don’t have a clue what that is.

One of the qualified techs on this forum will be able to help, I’m sure.


Your car is in open loop until operating temp. When the ecm takes over it may initiate the “pump”. Causing a major air leak or false air. Just a guess. A small air / vaccume leak can cause major driveability issues. I’m not a tech just trying to help.

Thanks for the comments. I’ll probably bring it in to a local technician to see what’s going on.

Perfect bscar. Thanks.