Hi i am new to this site and already have a question. I am working on a 1993 t100 3.0 and about 3 months ago i replaced the water pump and bypass tube. A couple of days ago this truck started to have a rough idle and when in gear it feels as if the truck iss going to die. I found that the throttle position sensor was bad and replaced it but did not help. I then pinched the fuel pressure regulator line off and the truck started running smooth so i replaced the regulator and it still has a rough idle. I can still pinch off the regulator line and it runs smooth. I hhave replaced the plugs and see no signs of water and it doesnt overheat. Has anyone had this problem.
Mark

 

Check the vacuum lines and deadend caps if there are any. Also clean the MAF as the A/F ratio may be off if there is an issue with the MAFand when you pinch the fuel regulator line you are adjusting it and making it run smoother, thus I would be inclined to say it is something to do with air.