New to me 1G Insight

[doctorgonzo]

I replaced the vacuum hoses to and from the MAP sensor and that seemed to help a bit, but not really. I replaced the coils with new Hitachi’s from Rockauto and it seemed to help a bit, especially before the engine got fully warm, but resumed bucking persistently whenever the engine warmed up. Then, I installed some new spark plugs, NGK Iridium from Autozone. Cylinder #1 had to be shimmed 90 degrees, but #2 and #3 had the ground electrode pointing at 10:30 or 11:00 o’clock (open end aimed at number two intake valve at 4:30 or 5:00 o’clock)

Well, I’m happy to report that I can now get it to go into lean burn about half the time, it helps if I turn off the air conditioner. I cruised up and down a long four mile drag with minimal stop signs and a 50mph speed limit
a few times and watched my 300 mile-old tankful of gas’s MPG improve a two or three tenths. I can run an indicated 40mph with the instant mileage at about 110-120 mpg. It will still buck sometimes, but I can, with a little effort, coax it into not bucking—it’s not as persistent as it used to be. It also seems prone to buck if I’m accelerating gently. I’d call it about 40% cured. I’m not getting any check engine codes, but I still have a hunch my cats are bad. Might have to remove them and visually inspect them and possibly clean them, and possibly replace them if they’re really messed up. Failing the cats being the culprit, I’m nearly at wit’s end.

[MetroMPG]

Did you ever replace the EGR valve? Sounds like the cleaning may not have worked on that part. The symptoms you're describing sound like you haven't sorted that out yet. The valve itself could be blocked, or the electrical traces that indicate the valve position status to the computer may be worn out.

[doctorgonzo]

Yes, brand new OEM EGR valve was installed, EGR manifold cleaning was done at the same time, then cleaned a second time to no avail. Being that there are no check engine lights being thrown at this point, I’m just sort of guessing at what might be wrong.