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Ask Jerry Your Own Question
Jerry, Master Mechanic
Category: Mazda
Satisfied Customers: 17220
Experience:  ASE Master certified, 30 years experience. Auto troubleshooting, electrical , ABS, SRS, EFI system
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my car has a rough idle what could cause this?

Customer Question

my car has a rough idle what could cause this?
Submitted: 6 years ago.
Category: Mazda
Expert:  Jerry replied 6 years ago.

Hello and welcome to Just, Super mechanic here. About your vehicle.

That could be one or more of the injectors that is getting a little clogged up. You would have to do an injector cleaning service to see if it gets any better at all and if so, then it is best to replace the injectors as a set. Or if it gets totally better, that would fix it.

Customer: replied 6 years ago.
Relist: Answer quality.
i want a refund of my 33 dollars
Expert:  Jerry replied 6 years ago.
What is your question?
Customer: replied 6 years ago.
This started all of a sudden, and if it is the injectors wouldnt it have gradually started?
Expert:  Jerry replied 6 years ago.
Oh, I see. Can you isolate which cylinder or cylinders are not firing?

Like by pulling the spark plug wires off one at a time to see if it lowers the RPM's


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  1. Listen for operation sound of each fuel injector with a screwdriver or a sound scope.
    • If no sound is heard, carry out the fuel leakage test.
NOTE: The best way to judge the performance of a fuel injector is to compare its sound with the sound of other fuel injectors.
Customer: replied 6 years ago.
ok the car runs fine while going down the road its just when its in park or drive with my foot on the brake
Expert:  Jerry replied 6 years ago.
OH....could it be that the engine is running okay but the vibrations are getting into the body/frame? Like a bad motor mount. Does it seem to run rough in reverse?
Customer: replied 6 years ago.
No, but could a clogged fuel filter cause my symptoms?
Expert:  Jerry replied 6 years ago.
No, the filter will normally give you a problem while moving, (surge)

I would think more of a vacuum issue or, throttle body, MAF or injectors. It will seem to run like an older car that needed a carburetor adjustment, (if your old enough to remember them, lol)

But, let's see. One good test for that when you don't have a propane tank with a hose, is to see if it runs any better when someone holds the brake and you spray a little throttle body cleaner in the intake. If it does smooth out, then you know it's a fuel mixture problem.

Also, I have had a couple of them where I had to take the MAF sensors out and clean them. They had a little bit of a rough idle and after cleaning the MAF sensors ran just great.