Hey guys, it seems like the motor is much smoother when it is raining or VERY humid outside. Things I have done so far, air filter, pcv, wires (not new a few months old), coil pack, plugs, CTS. Seafoamed the motor including the IAC, cleaned the intake. Everything is OEM except for the air filter.

Hey guys, it seems like the motor is much smoother when it is raining or VERY humid outside. Things I have done so far, air filter, pcv, wires (not new a few months old), coil pack, plugs, CTS. Seafoamed the motor including the IAC, cleaned the intake. Everything is OEM except for the air filter.

There are two things I can think of offhand. The first is that air density changes with humidity level, so the situation might be related to an air metering issue.

 

The second is that if the fuel you're using is slightly too low in octane rating, it might have a tendency to knock, and the ECU could retard the ignition timing a bit. When there's enough moisture in the intake air, it can somewhat reduce cylinder temperatures -- the cooling could reduce the tendency to knock, and allow the ECU to adjust timing to ''normal''.

I run 91 octane and always have. Also has a new knock sensor! I am going to go with the MAF sensor possibly being the issue. I find even at idle like it will be dipping sometimes and engine shivers, but when its raining, seems really nice and smooth the idle! When I pulled the MAF I accidentally touched the element at the end, although i was not sure if it was enough to damage it. I don't really have MUCH of a comparison since I cleaned it all the first day i brought the car home.

Make sure there are no intake air leaks after the MAF. Any air that gets pulled in that isn't metered is air the ECU doesn't know about, and the ECU won't provide fuel in the right ratio. That can definitely affect idle quality.

Hey guys, it seems like the motor is much smoother when it is raining or VERY humid outside. Things I have done so far, air filter, pcv, wires (not new a few months old), coil pack, plugs, CTS. Seafoamed the motor including the IAC, cleaned the intake. Everything is OEM except for the air filter.

 

Yes, humid air is denser with more oxygen, so combustion is better. People have notice that for a long time. 35 years ago, I had a small motor scooter with a 2 cycle motor and 50 cc displacement. Even with the scooter, I could feel more power and smoother engine performance when the air was damp.

For a particular temperature and pressure, the number of molecules in a volume of gas is a constant, and therefore humid air is less dense than dry air. (Hydrogen from the water has less mass than other air molecules.) Since the presence of water vapor displaces some portion of the other components of air, there isn't as much oxygen available to the engine for combustion. The mixture is then richer than it would be with dry air, and for many vehicles that results in ''better'' performance.

Edited June 9, 200916 yr by OB99W