Intermittent CEL: codes 25 & 26 (lean & rich) (1 Viewer)

[appleburger]

1994 USDM. Runs fine but the CEL has been coming on and off lately so I'm trying to troubleshoot it so I can get it inspected.

New symptom: CEL will often stay on after a warm startup and then go off after 10-15minutes of driving. Giving codes 25 & 26.

Related things done in the past 6-12 months: PAIR system removed, NTK O2 sensors installed in the manifold, EGR disabled/bypassed, harness near EGR secured, new intake tube, new charcoal canister, new plugs, wires, cap, rotor, and ignition coil, fuel pump, fuel filter, fuel pressure regulator, EFI relay.

FSM points to these things but so much of this has been redone with OEM parts within the past year with no symptoms until now. The fact it runs fine and the codes are intermittent is making this more difficult.
- Engine ground bolt loose
- Open in Ell circuit
- Injector circuit
- Injector
- Fuel line pressure
- VAF meter
- PAIR system
- Heated oxygen sensor circuits
- Heated oxygen sensors
- Ignition system
- ECM

I'm checking connections and air hoses and digging into the FSM but looking for other ideas/experience. Thanks!

 

[appleburger]

Update: Followed these two procedures from the FSM and got no CEL. I might be good for now. Hopefully it won't come back. Fingers crossed.

(1) Disconnect the EFI fuse (15 A) for 10 seconds or more, with ignition switch OFF.
(2) Initial test mode: Connect terminal TE2 and E 1 of DLC 1 with ignition switch OFF.
(3) Start the engine and warm the engine up, with ail accessory switches OFF.
(4) After the engine is warmed up, let it idle for 3 minutes.
(5) Accelerate rapidly to 4,000 rpm 3 times.
(6)Maintain 2,000 rpm for 90 seconds.
HINT: If a malfunction is detected, the malfunction indicator lamp will light up during step (6).

HINT: Before this test, check the feedback voltage for heated oxygen sensor.
(1) Disconnect the EFI fuse (15A) for 10 seconds or more, with ignition switch OFF.
(2) Initiate test mode: Connect terminals TE2 and El of DLC1 with ignition switch OFF.
(3) Start and warm up the engine.
(4) After the engine is warmed up, let it idle for 3 minutes.
(After the engine has started, do not depress the accelerator pedal.)
(5) Accelerate and maintain at 2,000 to 2,300 rpm for 2 minutes.
(6) Drive the vehicle at 88 - 95 km/h (55 to 59 mph) for 2 minutes.
(7) Stop at a safe place and idle for 2 minutes.
(8) Accelerate and maintain at 2,000 to 2,300 rpm for 2 minutes.
HINT: If a malfunction is detected, the malfunction indicator lamp will light up during step (8). NOTICE: If this procedure is not strictly followed, you cannot detect the malfunction.

 

[skw6r]

If you unplug your O2 sensors does it still occur?

 

[voodu3]

@OTRAMM
Has a video on this that should help.