73.5 CIS Idle minor idle hunting, why?
 

My CIS 73.5 9ll has just started to idle hunt ever so slightly but I thought I'd try to see if anyone had a suggestion as to why so I could catch it early. I hear it but it barely moves the tach. I'm guessing 100-200 RPM.
Thanks

My guess is a slight vacuum leak. Start by checking the big rubber boot on top for any cracks. Make sure all the screws are tight on the clamps. Then check the intake runner rubber connectors for any signs of cracking as well.

You can also carefully spray some carb cleaner around the rubber fittings while the motor is running. If the idle suddenly increases, chances are you found the leak. Keep a fire extinguisher close by as carb cleaner has the small possibly to ignite, although I have never had that experience.

Often idle hunting on CIS cars is a sign of a too rich mixture.

If the temps where you are were up recently (and/or the humidity), it may have just caused the mix to be a little rich for the ambient conditions. If the hunting goes away when the temps drop that might be it. You may need to lean your mixture a little.