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Q: Car misses and has a rough idle - 2001 Saturn L100

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My car has been missing and has a rough idle. I changed the plugs and also put in some expensive dry gas x2. Even though this is a Saturn, I had purchased it at Kia dealership, so I went to them. They said I had installed the wrong plugs and they replaced with the correct ones. When I’m driving at highway speeds, the car still misses.

I took it to the Saturn dealer and they reported that they had found the problem to be the ignition coil and performed the repair. The missing problem seems to be solved; however, my car still rough idles. What can I do to solve this rough idle?

A: Hello. There are several things that could ...

Hello. There are several things that could be causing your rough idle condition and therefore there are multiple possible solutions. Carbon buildup inside the intake manifold and valve train is a big cause of rough idle. This can usually be resolved by running a fuel system cleaner through your engine.

The wiring to the ignition coil could be damaged causing the rough idle you are experiencing. It is also possible that when the spark plugs were replaced, they were not gapped correctly which can also cause a rough idle.

I would recommend taking your vehicle back to the place that inspected the misfire issue and explain to them that you are still experiencing a rough idle and ask them to take a second look. You may be fortunate enough to have the issue resolved under warranty and at no cost to you. If you would rather have this looked at elsewhere, a certified professional from YourMechanic can come to your home or office to diagnose the rough idle and have this issue corrected.

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