Honda Repair: engine idle problems, vacuum gauge, vacuum leak

Question
Dear Bill,
    I'm getting back to you about the engine idle problem.
I have checked for a vacuum leak but found none. I hooked up a vacuum gauge to the system and got a steady reading of 19 hg. The gauge needle didn't float or drift but remained constant. Is there anything that I am missing? Could a bad alternator cause the reving of the engine because it's trying to recharge the battery or is the engine reving to compensate for the bad alternator?  

Answer
Michael:
Here are some other things to check for. Make sure the EGR valve is okay, check the air filter to make sure it is clean. Check the fuel pressure to make sure the pump is working okay. Check the cold advance solenoid valve and the fast idle control solenoid valve (ICSV). When the idle speed is low because of electrical or other loads on the engine the ICSV opens to allow more air into the intake manifold. This allows the idle to increase to its normal speed. The valve also reduces fast idle during warm-up. To prevent rough running after the engine starts the valve is open during cranking and just after starting to provide additional air into the intake manifold.
The alternator could make some difference, but I do not think you should get anything that noticeable.
Hope this helps. Let me know if I can be of any more assistance.
Bill