# Rough Idle when heater turned on?



## spthomas (Dec 21, 2006)

This is a new one on me. I just got my 240SX running again after two years. New plugs, wires, new catalytic converter, oil change, fresh gas. Idles and runs good. UNTIL you turn on the heater (not AC, just heater). When you turn on the heater fan, it idles TERRIBLE races the engine, then dies. But turn off the heater, and it works great! Any ideas?


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## Asleep (Jan 19, 2003)

are you sure the compressor isnt kicking on? do you have the vent settings on defrost maybe?
check the condition of your idle air control valve as well.


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## Trippen (Feb 21, 2006)

Sounds like Asleep was saying check all your vacume lines...Sounds like one is cracked not connected etc etc......Check them all because it maybe more then one...Also Does it do it when you are standing on the brakes??? This is vacume operated too.


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## tyrodtom (Jul 23, 2005)

Most manufactors make it engage the ac compressor when you turn on the heat, the little doors inside the dash just don't open and let the cool air into the car. The AC compressor last a lot longer that way, they don't go 6 months without lubrication.


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## Asleep (Jan 19, 2003)

they actually make it engage the compressor on the defrost setting. that way, youre blowing _dry_ and not humid, heated air onto the windshield glass. it will defog faster that way.


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