I have 2001 Nissan Altima, car runs very smooth, except it vibrates abnormally at idle speed, tachometer shows 750 rpm to 500 RPM,If I speed up idle speed to 1000-1100 rpm , the vibration is gone. What is wrong? Thanks in advance. Regards! Ho

You need to find out the procedure for setting the idle rpm on your car. On today's cars, the procedure is not always straight-forward. It likely involves the Idle Air Control Valve. Here's the procedure for Civics, to give you an idea of what may be involved:

https://www.askmehelpdesk.com/cars-t...tml#post219948

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Originally Posted by Peter Ray

I have 2001 Nissan Altima, car runs very smooth, except it vibrates abnormally at idle speed, tachometer shows 750 rpm to 500 RPM,If i speed up idle speed to 1000-1100 rpm , the vibration is gone. What is wrong? thanks in advance. regards! ho

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I have the same problem with my Altima. Did you fix the problem? If so, could you tell me what you did ?

I had the same problem. The idle was going up and down. Leak on the Intake manifold gasket (need to replace it).
Then problem with idle low about 300 to 400 RMP. Had to replace the idle air control valve. Also did a Fuel Air Induction Service and tune up. Car is great! Runs like new. Nissan dealership said Idle air control valve cannot be adjust. The car computer does it. Is it true?

Yes, ECM totally controls the IACV.