:banghead: My name is Gary. I was a auto technition for 25 years. Quit in 97 so I need some help.

I have a 96 Windstar with a 3.8 Ltr eng. I had a trouble code 1538 and the eng ran rough at idle.I replace the frt. intake manifold runner control actuator. It ran very good for a few days. Now I get a 1537 & 1538 codes when the check eng. lite comes on which is not all of the time. I did not have vac. at either actuator when the codes were there. I cleared the codes. The eng. is running fine right now. The last time it came on was 2 days ago so it is intermitent. When the codes do come on the eng. runs as though there is a vac. leak but I cannot find one. Question: Is there vac. to the runner control actuators at all times at idle or just at certain times?
Can someone help me before I go nuts trying to find and correct the problem?