Hi,

I don’t think in 1989 that the OBD was that sophisticated to monitor the gas tank pressures in relation to the cap being loose.
Emission checkups only tested the cap and the tank line from it to be pressure tested manual from the evaporative canister under the left side of the front bumper.
The fix was the seal on the cap, the line from the fill pipe up to the vacuum operated tee on the canister.
There’s no sensor at this time of smog checks to accomplish keeping the technician honest.
Because they weren’t honest or diligent we had to get that added on to our car prices.

A code for or of too a rich or lean mixture is a catch-all for vacuum lines being bad.
This along with other issues can be considered fun and games but not insurmountable.
That code is like a “shot gun blast” at being “diagnostics” that hits a wall of a barn. You have to go looking up and down, from end to end, of the whole barn or in this case the car.

It is a known issue for the rubber lines to that canister up to the engine to be rotten badly by this age car.

Have you read the black box? It has a blinking LED light inside it under the hood. It’s up by the brake vacuum booster area.
There are simple instructions, in service manuals like Bentley, to guide you through reading up to three codes in memory.
I think it’s three in my memory? (:-)

Punch in OBD codes into the FAQ for 700-900 search box it might take you out somewhere.

Others can help get you on the right highway to finding the issue.

My browsers or something in the site has stopped me from taking a peek at your profile to how long you have been posting or what state you are in to help you more.
If you are a newcomer or the site is down in that area, we have trouble linking prior posting issues to diagnose what the problem might be.

I hope it get fixed in that it’s a helpful tool.
Information in troubleshooting is always quicker.

Phil