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Jerry, Master Mechanic
Category: Car
Satisfied Customers: 17219
Experience:  ASE master, 30+ years. All makes and models. Trouble shooter, shop forman, service manager
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Mitsubishi galant: rough idle..timing belt..spark plugs, crank sensor

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02' mitsubishi galant slightly rough idle while car is in drive. timing belt , fuel pump, spark plugs, crank sensor have been mfi light on. no codes on the car. idles at a steady 700rpm when in drive. car has an automatic trans. oxygen sensor (before cat.) has been changed. car idles good when in park and drives excellent!! i am a home mechanic with good (not expert) experience with cars. help please!

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

Could it be that you are feeling the engine vibration more than you should?

Like a motor mount? Can you feel it in reverse?

Will it go away if you give it a little gas while holding the brake in drive?

Customer: replied 9 years ago.
Hello Super mechanic. rough idle does not go away if you give it gas while holding the brake in drive, however it does get a little better. plus now i am getting a mil with code po303 which is misfire in cylinder #3

That will help to narrow it down. You want to make sure there are no vacuum hoses that may be cracked or leaking. You might want to switch the coils and see if the code changes to a different cylinder.

Look at the spark plug boots to see if there is any small cracks in them. If it is not ignition related then there might be a problem with the #3 injector, maybe clogging up or a bad connection at the wire.

Jerry and 5 other Car Specialists are ready to help you
Customer: replied 9 years ago.
great advice i will try your suggestions tonightn when i get home and let you know. thanks
If you can duplicate the miss, you may want to try just tappping on the injector to see if it will help. If need be you might want to check the pulse at it and at worst, switch injectors around, (a last resort) let me know how you do, thanks
Customer: replied 9 years ago.
Hello again, well I pulled the injectors off cleaned them & switched the coils around. car runs about 15% better but rough idle is still there. code po303 also showed back up after 35 miles of driving. I have noticed that when the a/c is turned on the engine stays at the same rpm(the extra load by the a/c compressor is not being compensated for)i'm going to check the bolts around the intake manifold to make sure no air is getting in there.

If it got better with the injectors being cleaned that might be an indication that they are dirty, on the inside.

The best way to clean them is to runa cleaner through them. There is a micro-screen inside them.

As far as the idle problem, not compensating. You might want to do a good throttle bldy cleaning on it. The idle air control valve may be gummed up and getting slow. See if that will help it to run better too.

Customer: replied 9 years ago.
ok, finally did a compression check and found 125psi on all cylinders but #3. the #3 cylinder had 80psi. so i guess i have a bad valve. i will be pulling the head off this weekend and having it checked. thanks for your help!