Rough/Low Idle when damp out?

[Dean407]

Hi folks,

I have a 2007 CE 5spd. While I change the oil regularly, I haven't had any sort of 'tune-up' done on the car. I have about 57k and regularly get 38-40MPG as I do all highway miles.

The only issue (aside from a squeaking belt) is that when it's been raining (typically), I'll get a rough idle/low idle. When it starts, it goes to a high idle just fine. After driving a bit, at a light it will drop to say 500rpms and feel 'rough' then go up and down a little. After a while of driving this will smooth out.

But it is annoying as the car runs perfectly outside of damp weather and well after it's warmed up in damp weather.

Any suggestions?

BTW, I installed cruise control per the threads here and I use it 98% that I drive as I'm in a rural area and love it!

Dean

[Dean407]

Nobody has any suggestions?

[mikered30]

What intake and filter do you have? MAF dirty? Could try to replicate with a spray bottle on a dry day? Could be bad coil or dirty throttle body. Might want to try cleaning MAF, TB, and PCV valve.

[invader]

Do you rotate your vent selector knob from panel and/or floor vents to clockwise of floor position and up to floor/windshield and windshield position when it rains and when it's damp to defog the windshield? That causes the A/C compressor to cycle on and off, affecting engine idle... A ground upgrade helps stabilize idle speed. I also modified the vent selector cam to have A/C cycle on and off at only past floor/windshield position.