'93 Geo Prizm (Toyota 1.6l) emissions... High NOx and EGR valve?

This car failed emissions for high nitrous oxides. Limit was ~1300 and it was puting out ~1400. I was thinking it may be the EGR valve, but I can not find the EGR valve on this car. I'm beginning to wonder if it even has an
EGR valve. I can not find anything even remotely resembling an EGR valve near the throttle body, or anywhere on the intake. From waht I can see below the intake there is no EGR valve down there either. I also can't find any exhaust pipe from the manifold or even farther down from the exhaust pipe. Nothing that would lead to an EGR. Now I can't see everything down there around the exhaust and I can't see everything behind the engine, so it may yet have an EGR valve. Anyhow, if anyone knows whether it has an EGR valve and if it does, where it is, I'd really appreciate the information. I kinda think it must have one as the parts stores list an EGR valve for it and can order it.
If it's not that then I'm thinking it may be the catalytic converter. If that's the case maybe I'll just try retarding the timing a bit and see if that gets it to pass. I'm not gonna be keeping the car too much longer. Since it's only 100 over maybe the retarded timing will be enough. Just want it to pass to last a while longer.
Cory
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Cory Dunkle wrote:

Look on the backside of the intak manifold, facing the passenger compartment, down low.
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Cory Dunkle wrote:

If you don't see it on the back of the intake near where the throttlebody bolts up then I would suggest your model doesn't have one. This is the same 4AFE that Toyota builds for their Corolla; sometimes the Corolla version came without an EGR valve. I never paid attention to why some models had them and others didn't, but this is an oddity with the 93-97 body style Corolla.
Consider the possibility that you are running lean; inspect O2 sensor voltage for a high voltage bias (reduces injectors on-time) or weak fuel pressure.
If your emissions test is only performed at idle, check for vacuum leaks and check timing as you suggested. If you have a three wire TPS it may be sticking off of the idle contact when the throttle is closed. This condition tells the ECM you are on the throttle and changes timing to an incorrect value.
Make sure your vehicle is running at the proper coolant temp. High temps tend to push NOx higher.
Toyota MDT in MO
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just a reminder the 1993 corolla's and prizm's came with the 4afe and the 7afe the 1992 corolla's and prizm's came standard with the 4afe and the GSI with the yummy 4age high comp small port.
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I'd also consider replacing the O2 sensor if it is one of the types that screws into the manifold. I did this on my last vehicle and it cost me $30.
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As Philip said, it appears to sit low behind the throttle body. I have a diagram in front of me, and that's where it appears to be.
Steve
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New info....
There are four vacuum lines coming off the top of the throttle body. Two of them go towards the back of the engine bay, and hook into the EGR valve.
Steve
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Thanks, I'll check on that. I don't recall any vacuum lines off the top of the throttle body though. I may not be remembering correctly. I'll check on the location you mention and try to follow those vacuum lines. Is it below the intake manifold, as in attached to the underside of it?
Cory
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Ya, it looks like it's bolted to the intake just behind the throttle body.
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