I've been reading that(thanks) and I think the problem (due to other symptoms such as 1-2 shift bogs down) is that the Vacuum modulator assembly needs to be replaced as it looks like the original part.(def clean out the screen first, though.)
If this fails, it's off to the exhaust shop to unhook the cat, o2 sensor(have plate for that hole), and exhaust and run some seafoam or similar to blow out the carbon and gunk.(don't want that crud in the cat, sensor, or muffler, naturally). Because the only thing that will fix it at that point is getting rid of the crud in the cylinders. With 200K on the engine(runs perfectly fine as 75% of that is highway commuting) and no other symptoms, if it's not the EGR, then it's just full of gunk that I need to blow out.
Though, I hear that Toyota sells a similar product (engine pre-tune IIRC) that supposedly does the same thing for cleaning the throttle-body. Any experience with either of these on old engines?
EDIT - I found some before and after pics. The stuff seems to work to get out maybe 30-40% of carbon at most on a dirty engine(far from a miracle cure), but def needs to be run with the exhaust parts you want to save OFF of the thing. Apparently using it and clogging your cat is a fairly common "oops". The stuff itself won't cause any damage, but the junk it spews out certainly will cause all sorts of ills.
Before you go pullin' your truck apart lets check afews things first.
1. Have you checked to see if your EGR valve is working?(some times they get stuck & you have pull it off and clean them out)
2. Check for proper vucuum line routing and check for any damaged(cracked or blocked)vacuum lines also check the vacuum switch.
3. Use a vacuum gauge to see if you have vacuum at the EGR while driving.
4. Check the vacuum modulator operation.(see shop manual if you have one)
5. Check for any damage to the cat.
Some other things that can cause high NOX are higher than normal compression from carbon build up in the cylinders.
In that case a cylinder de-carb may help.
A high flow exhaust (header, high flow cat, larger exhaust tubing) will lower the back pressure,
which may have an effect on EGR operation. (check for enough vacuum at the EGR valve line)
Also larger tires without having the truck regeared to close to stock overall gearing will put an extra load on the motor
and increase emissions.
By the looks of those numbers it looks like the EGR wasn't working at low speed or the cat wasn't hot enough.
I know you said you drove it before the smog but how long did it sit before the test was started?
If it sat long enough the cat may have cooled down to much.
After checking that the EGR system is ok you might want to have a pre-test smog check run and make sure the cat is hot.
I sit outside the smog shop and run the engine at about 2,000 rpms untill he is ready to run the test.
I know it sounds silly but I have gone through alot to get my truck to pass due to all my not smog legal engine mods.
The state of california wants older trucks like ours to fail and get taken off the road.
I agree with trying to make our air cleaner and would love to convert my truck to cleaner burning propane,
but thats not legal in california.(go figure? sounds stupid to me). Anyway good luck with getting your truck smogged.
