Spray carefully around the engine intake etc. with (ether) starting fluid, any change in RPM and you've found a vacuum leak. Careful, that stuff burns!

Also, get some RedLine "complete fuel system conditioner". It is the ONLY fuel treatment that I have EVER found to work, my '91 started the soft-pedal thing at 60,000mlies, tried all of the solvent-based treatments, a bottle of RedLine actually made a difference (without causing damage to the engine bearings as Techron et al warn you on the bottle can happen).

Funny thing about the K-jetronic CIS system is that low fuel pressure will cause the engine to run rich, because the fuel pressure is used as counter-pressure against the air-flow meter. Can also be the frequency valve, unplug it and see if there's a difference, ... also, how old is the Oxygen-sensor?

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Gone to the dark side

- Jeff