Emissions Maint. Light

I'm in Simi Valley and need some technical help. I have an '88 limited 4.0L fuel injected (east coast if it matters). I have been fighting "Emissions Maint." idiot light for a week now. The manual only points to the Hot O2 sensor. I replaced it, replace the preheater hose. I have a new cat converter awaiting delivery. Any ideas? Maybe EGR valve? I have the Omix EGR, attached vacuum transducer. Don't want to spent the $200.00 if I can put it toward other needed components.:dunno:

Does it have Thermostatic air control?

I think that light on the Renix motors is triggered by a timer:

http://www.naxja.org/forum/showthread.php?t=30134

It does have the thermal switch mounted in the air cleaner if that's what you are referring to. It monitors the incoming air temp at start up. It could be the culprit, heck a lot of the sensors are 22 years old. It'll be cheap enough to replace. Thanks.

It's just on a timer. Reset the timer and the light goes out. On RENIX the timer is a mechanical gizmo in a box under the dash, replace the box to reset, or just discard the old one since there are no replacements available from the dealer anymore. On HO it's a flag in the computer that is reset with a scanner.