I have a 1990 f150. I have been trying to get it to stay running.without a hesitation. Every time I start it it hesitates and or dies. Ihave changed spark plugs rotor cap wires. Checked for vaccum leaks. And also changed the ingnition control module. I can get it to start and run at idle if it stays running for 15 minutes. But when KI take of i have to pump the gas to keep it from dieing. It has a major hesitation. But when I depress the cluthch it will idle okay. Sometimes it idles eratically. What else is there to try. I am lost. I listened for vaccum leaks but dont hear any. When I gas it up it hesitates and you gan hear air backing into the airbox but that is it.

Optional Information:
1990 Ford f150 L-6

Already Tried:
ignition control module, spark plugs, wires, distributor cap and rotor. Checked for vaccum leaks, also checked the map cylinder