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My Mazda 3 has suddenly been having rough idle issues. I have noticed that since yesterday, when my car is in idle it revs from the idle rpm(not sure if its 700-850rpm) to 1000 rpm then back again real quick. I can also feel that the car is misfiring and that there is a really foul oil smell from the engine.

I have also noticed a loss of power at 2nd gear when in manual mode(my car is an automatic). My car had a history of this same symptoms but it was due to a melted air intake pipe which was replaced. I haven't check it again but if it does not have any melts, then could the issue be from a faulty fuel pump?

I've talked to a couple of owners of Mazda 3's and they keep saying that this could be related to the fuel pump. But I don't want to have it inspected immediately as the costs to open the tank and check the pump is absurd in our parts.

Also earlier today, as I was completely irritated with the idling, I made a short "Italian tune up" by running to the redline on from 1st to 3rd, and it seemed that the rough idling stopped. Could this be a sign that it is not the fuel pump?

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    Is the car OBDII? Can you plug in a scan tool and interrogate fuel pressure? Or amps of current to the fuel pump?
    – Harper - Reinstate Monica
    Jan 13, 2017 at 0:31

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I would say that if you were able to take the car to the redline in 3rd gear, the fuel pump is providing sufficient pressure as the demands on the fuel pump are greater at full throttle than at idle.

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  • Found out it was the same issue I had as before, the intake pipe had a hole in it that's why it's not getting enough air to the engine.
    – marchemike
    Jan 13, 2017 at 5:09

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