the trim running way lean seems to indicate a possible leaky injector problem also check all the connectors. whats the LTFT cruising on the highway?

 

 

one thing you could try is a couple of bottles of techron fuel system cleaner. if LTFT improves injectors are probably leaking

 

 

O2 sensor can cause that, and so can the EGR valve not working right due to being bad, or from soot clogging it or the EGR rail on the intake. Both of those should place a code in the computer, but sometimes they don't.

The rich mixture would probably point more to the O2 sensor, and the hesitation/stumble would be much more pronounced than the EGR system causes, eventually becoming a drivability issue.

 

 

In my 93 Accord, the bad O2 sensor caused rich, lean, and everything in between. The computer had the IACV going crazy. Under load, I was bucking and lurching, barely getting it down the road. I think that was the lean mix. It also happened at 70mph, manifesting as a what felt like a repeated engine knock and gradual loss of power that required putting the car on the shoulder of the road to work the issue out. I think that was a backfire from the bad mix. I chased what I though was an ignition miss for 2 or more weeks until realizing it was a fuel system problem. My O2 sensor deteriorated so slowly over such a long time that the OBD1 system never showed it as bad. It would only show a code if the sensor was unplugged.

Yours could indeed be some other issue. If you haven't done it on that car, clean the EGR system. It's time consuming, but not a bad job on your year because I think you can take off the manifold where the soot builds up and clean it in your shop or on your bench. It was much harder on mine because of having to mess with the plugs in the manifold and take so much stuff off to get to them, then work hunched under the hood. I could also have taken off the manifold to clean it, but it's still not as easy as your, so I left it on and worked with the chicken wire and intake cleaner spray to loosen the crud and get it out of there, cleaning the EGR valve, and every passage in that whole system. The reason I talked so much about EGR is seeing the words "slight hesitation/stumble" in your first post. The EGR issue is more like that.

 

run a compression test, did you adjust the valves?

 

 

sure if you have a gauge check the rail pressure, but running rich its probably an injector leaking, however if the exhaust valve is too tight and therefore leaking it could cause the o2 sensor to also see a rich exhaust. the ecu would then trim lean.