Recently I've been getting an intermittent "Check Engine" lamp. I've run the EZK (terminal 6) fault code and I get a 2-4-1 which appears to be an EGR problem. I have tested the EGR valve under the intake and with manual vacuum applied, it opens properly and holds vacuum. I do not know how to test the electromagnetic vacuum switching valve on the left strut tower but it does not seem to manage the vacuum signal to the EGR valve at various (warm) engine speeds. The "Check Engine" lamp is intermittent because when I have driven the car and made several shut downs and restarts over the course of an hour or so, the lamp goes out. When I check the input voltage to the EGR vacuum switching valve at 2500 rpm, I get very fast, mixed voltages of 1 volt down to .25 millivolt repeating in a fairly concise pattern. I'd really like to avoid paying $160 for a new ($60 used) EGR vacuum switch but don't really think its the problem. BTW: I have new temperature senders on the block under the intake and warm idle is only occasionaly rough.

Any suggestions on EGR input voltages or likely problem areas?

Muchas Gracias