EGR system mystery malfunction

[timsch75]

I have an '88 Toyota Supra (non turbo)that I am working on to get it passed its first emissions test. It failed NOx by roughly three times the limit both at idle and at speed. It also failed HC by 50% more than its limit. I've searched the forum and assume from what I've found that the NOx is likely due to a malfunctioning EGR system, so that's what I've been trying to diagnose. I did find that the VSV (vacuum switching valve, I believe) was not functioning properly, so I replaced that. I read that if vacuum is applied to the EGR valve when car is idling, the car should run rough or die. I did this with no effect on engine idle. I did hear the EGR plunger moving when doing this. From this I thought that I had some carbon-plugged lines or ports. I took the air intake/throttle body apart down to the intake manifold looking for blockage, but found none. Every port and line I blew compressed air through was open, although I couldn't really tell where the air was going when I blew through the port in the engine, it was not blocked. While I had hte EGR valve out, I tried to blow air through it's passage w/o vacuum, and there was no flow, but when I pulled vacuum, it allowed flow, so it definitely appears to be functioning properly.

The only component that I found to be possibly malfunctioning was the vacuum controller modulator, although it passed all tests but one, and that test description was vague (air passage at idle but "resistance" to flow at 2500 rpm. it didn't specify how much pressure this could resist, and it passed 90 psi).

What else could be the problem with my EGR system that it would not be running rough at idle when pulling the vacuum if the EGR valve is functioning properly and the lines are open?

[The Dude]

Did you try looking at the EGR Port down at the exhaust side. There is a small port that can get blocked off. But you obviously have another problem because the EGR does not come on at idle and you said you failed Nox at idle. The only way to produce Nox is by having to much heat in the combustion chamber. This is how EGR works, it introduces exhaust gases (dead air) back into the cylinders to drop Combustion temp., but it only comes on at cruise.

[timsch75]

I have not looked at a port where the exhaust gas comes from the exhaust system. I did blow air from the port that goes to the inlet of the EGR valve, which should be directly linked to the exhaust port you mention. It did allow air to pass, and unless there is some bypass in this link, then the exhaust side port should be open.