1998 Mazda 626 Rough Idle

Tiny
MNDANDREWS
  • MEMBER
  • 1998 MAZDA 626
  • 6 CYL
  • FWD
  • AUTOMATIC
  • 14,000 MILES
My daughter drives this car while she is away @ college. We recently replaced her timing belt and water pump. When we picked it up from the mechanic, we were told one of the engine mounts was broken, the car would run, but it would be rough while in gear but not moving (say like at a red light). Boy was it rough. We had the engine mount fixed, but it is still rough while in gear and stopped (again, red light) but much improved over what it had been. When the car is moving it is smooth and sweet. Lately she has had a check engine light come on and the auto 'zone' type stores tell her she has a mis-firing 3rd cylinder. We have all new spark plugs and wires. I put some slick 50 fuel injector cleaner in it about 300 miles ago. Are these two things related? Could the rough idle be a transmission problem (it's about the only thing I have not fixed/replaced on this car yet! ;-} )
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Wednesday, October 14th, 2009 AT 1:50 PM

4 Replies

Tiny
RASMATAZ
  • MEMBER
Misfire at cyl no.3 -check the compression and injector on that cylinder

Engine misfiring can be caused by worn or fouled spark plugs, a weak spark (weak coil, bad spark plug wire), loss of compression, vacuum leaks, anything that causes an unusually lean fuel mixture (lean misfire), an EGR valve that is stuck open, dirty fuel injectors, low fuel pressure, or even bad fuel.
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Wednesday, October 14th, 2009 AT 2:20 PM
Tiny
MNDANDREWS
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So you don't think it is the transmission? That would be a relief!

Besides the fuel injector cleaner, what do you recommend for my next step? The spark plugs and wires are new with in the last month. It just passed it's safety and emissions inspection too. (Passed the day before the engine light came on, and 5 days after the code had been previously cleared.)

We get the 85 octane gas. Because of her high mileage should we buy the higher octane gas?
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Wednesday, October 14th, 2009 AT 2:50 PM
Tiny
RASMATAZ
  • MEMBER
Lets check the compression and injector on that cylinder-if it was a gas problem it will affect all cylinders.
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Wednesday, October 14th, 2009 AT 2:53 PM
Tiny
MNDANDREWS
  • MEMBER
Cool!

She is bringing the car home this weekend from school, I'll have her stop by the mechanic and have him check out the compression and injector on that cylinder.

Thank you so much for the help. I will let you know how it goes after Friday's visit! ;-)
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Wednesday, October 14th, 2009 AT 2:57 PM

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