Black94sc2

94 SC2 recently idles rough but runs fine when not idleing. Any ideas on what the cause may be?

PurdueGuy

what tune up stuff have you done before, and when?

Black94sc2

I havent done any tune up stuff since I have had the car 18 months. I have no idea when it last had anything done.

PurdueGuy

you may want to start with plugs (NGK V-power, or regular NGK are a good choice. Avoid anything platinum), plug wires (don't really need anything spectacular here), air filter (cheapie will do unless you want to do an aftermarket intake), oil & filter change (avoid FRAM filters), if it's an automatic - a tranny fluid & spin-on filter change (though this won't affect rough idle, it's just good for tranny longevity). You may also have an issue with the engine coolant temperature sensor (ECTS), which is prone to failure in the S-Series.

Artificialist

Possibly the engine mounts are bottoming out, and the metal-metal contact transfers vibration.

Put the car in D, with a foot on the brake, and get the engine to around 1500 RPM. Have someone tell you if the engine moves drastically. D the same in reverse.

If you car is a manual, put the car in first and keep one foot on the brake. Rev up to 1500 RPM, and release the clutch a little. Have someone tell you if the engine moves too much. Do the same in reverse.

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ION II 5AT with 2.5 inch stainless exhaust piping, Magnapack resonator, and Flowmaster Hushpower muffler.

brad_bb

Just to prevent from replacing parts unnecessarily, you can check the resistance of plug wires with a multimeter to measure the resistance. This will tell you whether you need to replace wires or not. The spec is in the manual. I recommend you purchase a manual like a haynes manual from Pepboys or other auto parts store that carries them.
I have had my engine run very rough when I first started it after letting it sit a couple days or more without running. I'm not sure exactly what causes it. Wet plugs not firing right away? Moisture in conbustion chamber? Not sure. After a minute or two it smoothes out. Is your rough idle constant?

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Brad_bb

Artificialist

Sometimes when a car is left off for a few days, the weather changes, but the fuel and spark trim hasn't. The computer needs some time before it can set those back to normal.

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ION II 5AT with 2.5 inch stainless exhaust piping, Magnapack resonator, and Flowmaster Hushpower muffler.