i have a 91 E250 with the 300-6 cyl.some times after i start it it will stumble and die and some times it wont.and for the other problem,after it has idled for a while it will stumble or die when i put it in gear.you guys are great so i know some one will be able to solve my problem TIA!!!

 

Probably the IAC or TPS. Take out the IAC and clean it and clean the spot where the IAC goes in. TPS can't be cleaned just replace it if it is bad.

 

Here's a tip too.

Reset the computer. #1 With Engine NOT running,Turn the headlamps on, disconnect the negative battery cable. #2 Wait 15 minutes... #3 turn light switch off, reconnect negative battery cable. #4 Start Engine, let idle for 3 minutes. and U R ready to go.