My 88 Pathfinder recently went into fail safe mode (won't go above 2750 RPMs). The computer code was 51 - bad injectors, although the car idled fine. I cleaned and replaced the injectors, no more error code, no more failsafe mode. However, now the vehicle idles VERY erratically - fluctuating between 1200-1800 RPMs continually. There are no vacuum leaks, fuel pressure is good, ignition timing is good, choke functions. I even switched out computers. What would cause the idle to go so bad immediately after replacing the injectors? I'm baffled...

Check Ignition RPM Module:

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Sounds like a switched vacuum supply. Look into the map sensor. Sounds like manifold pressue is changing rapidly.