Suggestions re: RPM Drop @ Idle

[2007ZX5]

Hi folks - Looking for your advice for my 2007 ZX5 with 120,000km.

The issue is a drop and fluttering of the RPMs while stopped. The issue doesn't occur while in 'park'. I do notice a more active and aggressive dropping in RPMs with dampness or after rain.

Am I looking at a potential misfire in the spark plugs? Any suggestions for a do-it-yourself fix without having technical know-how?

Thanks in advance for your suggestions!

[Sponsor]

[whynotthinkwhynot]

That car is equipped with a lifetime (in theory) air filter. You should read in the owner's manual how to test it, and test it to make sure it's good.

I did start having problems with my spark plugs right around the same time in mileage. If those are the factory plugs, then yes, it could be something due to the plugs. It could also be due to the coil boots- what goes for spark plug wires in these cars that have coil on plug ignition. Both parts can be replaced. Plug boots were about $5-8, and plugs should be about $3 for platinum plugs. I suggest you get Autolite 104PP plugs, that's double platinum plugs, or factory recommended Motorcraft plugs.

[2007ZX5]

Thanks for the reply Whynot,

I've gone ahead and replaced the spark plugs, with the car reacting very well to begin. The same issue of rapid RPM drop/fluctuation at iddle returned and occurred for a while until the outside temperature dropped in October. With the the cooler and dry weather, the issue has disappeared.

Would that lead to an air filter concern, even though the air filter indicator seems to be okay?

Thanks again for the advice in advance.