i have a 99 silverado it runs fine in the summer but when its cold it idles up and down in park and in drive it dosent go a way till the weather get warn agian. any ideas

i have a 99 silverado it runs fine in the summer but when its cold it idles up and down in park and in drive it dosent go a way till the weather get warn agian. any ideas

is the idle problem continuous??? when cold..or only until engine is at normal temp ??

what is the spread hi/lo RPM's...

the IAC and throttle body should be cleaned periodically...have you ever done this..?

Check PCV/hoses and other sources of vacuum leaks and/or air duct leaks..

ECT may be out of range....