EGR problems

Hi, all.
I've got a 97 M with a check engine light on.  AZ says its an EGR code--I didn't get the number.  The car runs great; if there was no MIL, I wouldn't even know there was a problem.  Here's what I've checked (to no avail):
1.  The valve and ports are in good shape--I can kill the engine by manually actuating the EGR valve.  Also the diaphragm holds vacuum w/o fade.
2.  The solenoid pair on the Pass. fender well check out--the outboard one opens w/ voltage applied, the inboard one seals.  I did not know where to apply voltage to the third (boost?) solenoid, so did not test.
3.  The sensor on top of the EGR valve seems OK--I get resistance change when I push on the steel pin.  I think I got somewhere around 2.5-2.7 Ohm max.  One pin seems to be common and the other two work in opposite directions (one is normally open, the other normally closed).
4.  The vac port on the intake manifold is not clogged--strong vac detected w/ gauge.
Should the EGR valve operate when I rev the motor (it doesn't)?  If I have good vac from the intake and functioning solenoids, then the solenoids must not be activating, right?  If the EGR sensor is functioning, could a bad TPS cause the solenoids not to actuate?  And finally, How do I REALLY know the EGR sensor is good?
Thanks!

The egr valve should be closed at idle and at wide open throttle.  I should open at part throttle as if you were in a steady state cruise down the freeway.

Originally Posted by decentdissent
Hi, all.
1. AZ says its an EGR code--I didn't get the number.
2.  I think I got somewhere around 2.5-2.7 Ohm max.
3. One pin seems to be common and the other two work in opposite directions (one is normally open, the other normally closed).
4. The vac port on the intake manifold is not clogged--strong vac detected w/ gauge.
5. Should the EGR valve operate when I rev the motor (it doesn't)?

1. That would have helped. Most likely P0401 No EGR flow.
5. Probably, but can't say for sure. A few don't, but not many. You should open to about 1/3 to 1/2 throttle.
4. If no vacuum, plug the vacuum gauge to the EGR vacuum hose where you can see the gauge while driving safely. Drive with a warm engine, and watch for vacuum. If you still have no vacuum, the problem is in the control side. You need to find out why. If you have vacuum, time to check the sensor.
2. Resistance seems very low. Are you sure its not about 2.5 quot;kquot; Ohms?
3. The pin 1 is ground, pin 3 is reference voltage. The voltage at pin 2 is the one that the computer looks at. It should change with EGR position.
3a. Check voltage across pin 1 amp; 3 at the harness, unplugged with the key on. I think it should be 5 volts.
3b. Check voltage at pin 2 plugged in. Should change with the diaphragm position.
Get back to us with what you find out.
Alan

Thanks, guys, for the replies.  It'll be raining in SE Alabama for the next few days.  I cant put the vac gauge under the wiper and I really don't wanna go the duct tape route.  I will perform the tests you mention as soon as weather permits.  I can probably make time for the electrical tests sooner.
Thanks,
Al

Well, the rain still hasn't let up, but the check engine light went off today of its own accord.  Maybe there was a chunk of carbon holding the valve open and causing the position sensor to go out of range.  After a while, I guess, the carbon fell out and I turned the key enough times to clear the code.  While I've never seen it happen in a Miata, I have seen it happen.  I guess for now, I'll just keep an eye on it.  If the code trips again, I'll go back to the advice in this post.
Thanks,
Al