Hi all. I apologise for what may turn into a long post/rant, but I'll try to be very descriptive.
First the numbers:
%co2 %o2 hc (ppm) co (%)
test rpm meas meas max gp meas max gp meas results
idle 702 12.70 1.8 120 270 431 1.00 2.50 0.26 g pol
2500 2455 13.08 0.9 140 290 261 1.00 2.50 0.68 fail

So first I hooked up my sears multimeter set to the FREQ%duty setting to the x11 connection (red#3, black #2) and I get 81.35 when the key is on/engine off or at idle. No change.

Then I hooked up my self made code reader (thanks Arthur!) to the x11/4 and I get 16 flashes. According to the factory service manual this is "EGR switchover valve (Y27), open/short circuit." I installed another(used) switchover valve and the promlem persists.

The EGR valve itself is functional when I apply a vacuum pump, and I cleaned the pipe @ 75k miles when I changed the head gasket. The car now has 110k miles.

At first I thought it was 17 flashes so I changed the o2 sensor and of course that didn't help. The old one had 40k miles on it.

One more thing that confuses me: When I took the car to get tested the check engine light worked at start-up as it should, and then go out. Two days later it doesn't light up at all.

Any ideas or advice would be greatly appreciated. Thanks in advance.