I Might Just Know What I'm Talking About
Join Date: Sep 1999
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Re: Idle problems Back! EGR?
As I understand it, most common failure mode of an EGR valve is not opening - the diaphragm goes bad. EGR valve typically doesn't open until motor warms up, at least with the standard CTO (coolant temp operated) setup.
Sounds like some items are still controlled by your CTO. You could simply unplug the EGR and plug the vac line going to it, and see if it helps - that would prevent the EGR from opening, and pinpoint the EGR if it is the culprit. What the EGR does, is let a fixed amount of exhaust gas into the intake. When mine was bad, it simply didn't open. This results in higher NOx emissions, but I can't see how it would make the motor idle poorly.
If I recall correctly, I think the CTO also controls how much, or which, vacuum (manifold or ported) gets to the vac advance on the distributor - not exactly sure on that one, but I think it (the CTO) plays some role. I would look more at this, in my opinion, than the EGR. Maybe when it switches over something is not working correctly, or your CTO is bad.
Could be choke, too, of course. ??
I'm not the all-knowing by any means, these are just my thoughts. [img]/wwwthreads_images/icons/smile.gif[/img] You can also remove these 2 funtions (vac advance and EGR) from the CTO - my weber/GM HEI setup doesn't use a CTO. I think this would just make the motor warm up slower, but the difference is likely minimal.
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