why the engine idles up and down ? on 1997 Lexus LS400

when the car is in park the engine will idle up and down, in gear it runs smooth but at a high idle, I changed the mass air flow sensar. What is causing this please ?

by in Port Arthur, TX on October 29, 2009
1 answer 1 comment
ANSWER by on October 30, 2009
You could have a vacuum leak, or something else that is effecting the air/fuel mixture. There is an idle valve that controls the idle speed, this valve or the circuit that controls it may be having problems. I suggest you have this diagnosed before replacing any more parts though, the idle valve alone is over $500!
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COMMENT by on February 09, 2011
thank you for your answer,i brought to dealer they say ecm and short circit,i replace ecm,air mass sensor and whole engine still the same,please help