Just curious as when it runs bad cold whats the temp like where you are at when cold ? I ask because I had problems in winter time cold weather in Md where I live whenever it was cold and damp. But mine was a carb on my 318 Ramcharger. My problem was my hot air intake on the air cleaner was not working and after the truck started within a few minutes it started running bad and chugging as I found out the door on the air cleaner was not closing to give me hot air from around the exh manifold and it was still getting the cold damp outside air. What happened was the carb throttle blades were icing up even though it would happen at 30 to 45 degrees. I cant remember but you 89 should be throttle body injection and may still use the heated air intake from the air cleaner. When hot the door stays open and the air in the eng come from the air cleaner snorkel but when colder that door should get vacum to it from a temp sensor in the air cleaner that lets the eng now pull hot air from around the exh manifold shield. And believe me it makes a big difference in the right temp days that can be damp and chilly and the throttle blades can ice up real easy with cold damp air going by them. After I fixed my hot air door I could start my truck and go in the house while it warmed up. Five minutes later it was still running great but when it was not working it would die in about 2 minutes and run bad until the eng and under hood was warm. Dont know if thats your problem but its worth making sure the air cleaner door is working right. Ron