Poor(No) Idle in Wet Weather

[fisherman11]

My 2001 XLT recently developed a problem that occurs after it sits out in the rain. The engine starts fine, but it won't maintain idle. Warming up the engine to operating temperature doesn't help. I need to run the engine for 20 - 30 minutes before the situation improves, so it seems it needs the engine compartment to get hot enough to drive off the moisture. I don't have the problem when driving in the rain.

Any suggestions?

 

[green03]

Does it run bad anywhere else when it is doing this? Off-idle, cruise, etc.

 

[fisherman11]

For the most part, no. After a while (20 - 30 minutes) I can generally get the car moving. When I come to a stop, the tach shows an idle around 400 -500 rpm. I seem to recall the normal idle is around 800 rpm. While it's in this condition, it is sluggish off idle and sometimes hesitates, but I attribute that to the low idle speed. Otherwise, at speed it runs pretty well. If I run the air conditioner, the additional load generally stalls the car when I come to a stop.
I have noticed the "Check engine light" comes on occasionally, but doesn't stay on long enough for me to get it to a mechanic to check the codes.

 

[green03]

I don't know what the rain would have to do with it, but sounds like the Idle Air Control (IAC) if any other drivability isn't being hampered. It is a long cylindrical device usually mounted on the throttle body with a 2 wire connector. Snap a picture of under your hood and I will point it out to you if you can't find it. the test is while you are having the issues, unplug the connector off the IAC. If the truck doesn't run any worse that is your problem. sometimes they just stick and if you beat on it a bit while you are having the problems and it idles back up you can be sure it is sticking. You can then clean or replace it, but in my experience one that is really gummed up will never work right again and a replacement is about 45 dollars from autozone.
Matt

 

[fisherman11]

Thanks for the advice, Matt. I'll give it a shot. I have a Haynes Manual, so I ought to be able to locate the IAC. If not, I'll post a pic.

Thanks again.

 

[fisherman11]

Matt -

I tried out your solution and it works great! I took off the IAC and gave it a couple of shots of WD-40 to loosen up the actuator, re-installed it, cranked it up and the idle went right to 800. No stalls, works great with the A/C running, too. I'll get a replacement IAC, but this gets me running for now.

Thanks again for the advice. You saved me some bucks!

 

[green03]

They make some stuff called throttle body cleaner that will clean it somewhat, but never use carburetor cleaner... carb cleaner will eat the teflon piston and cause it to run fast all the time. Glad you got it licked....
Matt