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. Edited by: delco

</>I have the same vehicle....and I notice the same issue. On the coldest mornings it warms up and will idle (slightly advanced) just fine before I take off. Then, once I take off, it will occasionally stumble and not idle well the first few stops. A few minutes of driving and the idle problem and stumble problem completely go away. Again, only on the coldest mornings.


Sorry I'm not being much help. I suspect it might be thermostat setting related or temp sensor related.


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Edited by: glennb

I posted the message about the low idle problem. After pulling and reseating both ends of all vacuum hoses, I found several hose ends that were cracked and probably leaking. The hose is only 5 years old, and I used the good braided hose. There is a lot of vacuum hose and I guess I will be replacing some of it this summer. I cut the cracked hose back and I no longer have the low idle problem. while I was checking, I also noticed the ignition timing was wrong, it was at 8 degrees instead of the 12 degrees it should be. I corrected that also. Now it idles fine and no more hesitation.
I'll bet a large number of engine problems are caused by vacuum leaks.