Code 25 that comes and goes depending if the engine is warm.

Really interesting issue I have been battling.

Code 25, symptoms are on start up the exhaust reeks of fuel. If I don't let the car idle and get to operating temp before I drive it it throws a code 25 and goes into a limp mode. Now here's the kicker: if I pull over and turn off the car after it throws a code 25 and it's up to operating temp, once I restart the code 25 is not there and will not go then it drives like nothing is wrong... until I let it cool down, then I can repeat the same issue every time if I don't let it warm up. Also of not the exhaust still smells like fuel when warmed up but not as bad, and to be honest I'm not sure how much its supposed to smell like fuel being 30 years old and all.

For reference is a 93 3.0 with 318k so really any part could be failing.

Replaced O2 with oem Denso.

Did a smoke test and found one small leak that I fixed on the Power setting idle up valve.
Fixed and exhaust leak and to my knowledge doesn't have one anymore, it's hard to tell with how noisy these engines are.

Checked the Fuel pressure by jumping the diagnostic port and it did test high at 48-49 psi(I have one on order from Beck/Arnley) but it idles fine at 40 psi and climbs up to 50 psi when I rev it then goes back down to 40. Also it holds the pressure just fine for 15 min+ once turned off so an injector is not leaking.

My question is has anyone experienced this before? I know this is a heated O2 sensor so I'm kind of wondering if something is going on with that? Any help would be greatly appreciated.

 

Have you looked up code 25 yet? IIRC 25 is a lean running code. If the computer is thinking its running lean I can see it trying to adjust the fuel levels to try and richen it up

 

Here is the troubleshooting guide from the FSM.