Thermostat vs Engine Idle Rough When Cold


Old 05-03-11, 05:04 PM
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Join Date: Jun 2005
Location: United States
Posts: 327
Thermostat vs Engine Idle Rough When Cold

1990 Honda Accord LX, 4DR, AT, 216K miles. Would a defect thermostat (partially or fully open when cold) makes engine idle rough when cold and normal when engine reaches normal operating temperature? When idle rough, engine is shaking and want to stop especially at drive gear like D4 gear. Once it reaches operating temperature, it works normal. If not a themostat problem, what else to check? Any idea?
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Old 05-03-11, 07:54 PM
ukrbyk's Avatar
Join Date: Mar 2010
Location: USA/ Pacific NW
Posts: 3,189
idle speed control valve. i am speaking based of my 91 Civic. cleaning that valve took a lot of shake out. it is operated, at least in part, by coolant running through it. gets clogged, just like drain pipes.

also, you engine mounts are getting there.

i simply rig idle rpms a little bit higher. there should be a flat head screw either under carb or throttle body, if you have CFI engine.
Old 05-04-11, 03:08 AM
Join Date: Feb 2011
Location: usa
Posts: 64
could be lots of things put chevron injector cleaner through it. Gunk on the back of the valves can do this to

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