Hi, I live where the nights get very cold in the Winter.
I have this '88 Trooper II 4cylinder that is almost bulletproof. It has 188000 miles and runs very good after it warms up.
I have had this problem with a very low idle for 4-5 mins in the morning when the temp is below around 40f. It is getting worse.
When I first start it, it idles fine then after 30-40 seconds, the idle speed will drop to 300-400 rpm. It only happens in the Winter when the engine is very cold. The colder it is, the worse it is. Sometimes it will stall. If I just idle it for a few seconds and drive, the engine stumbles. Sometimes I have to warm it to melt ice and warm it a little inside. After it warms up it does idle and run good. I get a little hesitation once in a while even when it is warm.
A few years ago I blew a head gasket and I had the head milled and ALL the valves and most valve guides replaced. I replaced all the vacuum hoses and I used a teflon coated head gasket. I don't think it is a vacuum hose problem.
It actually sounds like the timing is being retarded.
I have a Haynes repair manual, but it isn't much help.
I am a good mechanic on older cars without all the emission controls.
Any help will be appreciated.