Mazda 3 2006 problem with engine

I have a mazda 3 2006 1.6 diesel that i got for cheap not long ago however i have ran into a issue recently

I go to my car in the morning to go to work and i turn the car on without a problem when after about 15 seconds of idling, the cars rpm keep going up and down (around 900 and 700) and it keeps happening until i press the gas pedal and it goes back to normal. It doesnt matter how hard i press it, it always goes back to normal.
It keeps happening until i take off and i get to work without a problem, the car drives normally and there is no issue when stopping and idling at a traffic light.
If i ever need to move my car at work, thats when it gets bad because the issue is worsened, the cars rpm goes up and down and the car will turn off after a struggle to keep running if i dont do anything.
If i try to press the gas pedal too much the car turns off.
A temporary solution is to gently press the gas pedal, you can hear the engine struggling to apply gas and the rpm doesnt go up by much but after a little bit i apply a bit more gas until it works(it really sounds like something is clogging the engine) then the car runs fine. I looked on the internet but no one describes the issue like mine. Anyone know whats causing the issue?

Are you in the USA??
I have never seen a Mazda3 diesel (that I remember anyway)…

1 Like

Im not in the USA im from Serbia
Its an older mazda 3, first generation so its not common in usa but in serbia everyone drives older cars

Yes, but Dave’s point was that diesel-powered Mazda 3s were never sold in The US, so it isn’t likely that anyone in this US-based forum has any experience with a Mazda 3 diesel.

1 Like

Thank you for the response…
This is a USA based forum so unfortunately you may not find much help… You might want to try to find a forum for Mazda Diesels…

This is the same PSA diesel engine as the Peugeot in the other thread.

No experience with this car or engine, but my guess is the throttle valve is moving into and out of the correct position at random for some reason. Maybe it is just sticking, then unsticking. Ask shop to check for deposits of gunk/carbon in the throttle valve area. If so, clean that area so the throttle valve is able to move freely.

I had a similar symptom on my much older gasoline Corolla years ago, caused by a faulty idle air control mechanism. An 06 Mazda 3 probably doesn’t use that part; done solely by the drivetrain computer’s throttle valve control.

On an 06 I’d expect this sort of problem, the throttle position sensor reading wouldn’t match up to what it was supposed to be, and the issue would flag a diagnostic code, and the check engine light would be on. OP, is the check engine light on?

Check engine light came on after a repair on the fuel injectors, i went to the store and they said that there is carbon build up in EGR valve… there is a thing called decarbonisation that i did not long ago and its supposed to clean the EGR but the check engine is still on.

If the check engine light it on, there’s at least one diagnostic code stored in the powertrain computer’s memory. Ask your shop to read what it is, usually of the form PXXXX, then post the number(s) here.

The EGR valve’s output is nearby to the throttle valve area, so the two issues may be related. Decarbonizing the EGR valve isn’t the same procedure as decarbonizing the throttle valve. If the EGR valve is sticking, this sort of symptom is possible. Usually however it would completely stall the engine, not just vary the idle rpm wildly.

@extrememiljan_185241, is your Mazda3 originally from the EU or a different part of Europe? I ask because that might help us understand the CEL codes.

You might need to remove the EGR and start the vehicle to make sure the flow to it is not clogged and also check the EGR valve itself to make sure it is not clogged to the point the cleaner didn’t work… Well on a gas engine anyway, I am not sure what all is involved with your diesel EGR system… It almost sounds like the EGR valve is a little suck open causing the erotic idle issue… I know that a Gas engine EGR will try to stall or have a rough idle if it is opened at idle, not sure about a diesel though…

A diesels worst enemy is the EGR valve as problems with it due to city driving happen pretty often

Most common issue on diesel engines is that due to carbon build up in the EGR, check engine comes on and the car loses power, leading to poor gas mileage and rough idle.
However my car runs fine, it doesnt use much fuel (ive literally put 10l of diesel about 2 weeks ago and still have quarter of a tank left) and acceleration is fine, ive driven 130kmh without a issue for longer periods of time with no problem on acceleration and to top it off ive driven 2000 km as of now with the issue

I still think that some valve is clogged up due to carbon build up so ill see it taken out and cleaned throughly or perhaps some sensor is the culprit. Ill go to the store sometime to see what the error code is and hopefully solve the issue

1 Like

Since the diesel has no physical throttle, power is controlled by limiting fuel. Air is always available so any unintended, un-metered fuel will cause the engine to increase rpm and power output. The most common sources are blowby oil and oil leaking from a worn turbocharger , these then pool in the intake manifold. Engine hunting and surging at idle is often caused by A fuel delivery problems: Low fuel pump pressure, air entering the systems, clogged fuel filter,… Air leak and clogged air filter.

1 Like

The issue was actually a faulty EGR valve, it was stuck and was clogging the engine, had do buy a new one for 50 euro and the issue is gone


Suggest to ask your shop to check the egr valve as part of routine maintenance. Themost simple method is to just look at it when applying a test vacuum using a hand-held vacuum pump. With most styles you can see something moving. On some styles that won’t work probably, can’t see the moving part. The way I do the test is to apply vacuum when the engine is warm idling. If that stalls the engine , the EGR valve is probably working ok. Can’t speak to your mazda, but it has worked on my Corolla, Ford truck, and prior VW Rabbit. All gasoline engines though. I do this test every time I replace the spark plugs, as part of the tune-up procedure. Doesn’t take much time or effort.