I have had an ongoing problem with my 89 244, 195K miles. I'm the original owner. I get a check eng light approx every 7-10 days. I clear it by removing the neg batt cable. The codes from the computer are of no help, they are clear, nothing. Occasionally, I get engine hesitation, usually from an idle stop, or low speed like after turning a corner. To date I have been using the random remove and replace method in trying to find/fix the problem. I have cleaned the IAC, throttle body, new plugs, new crank position sensor, new FPR, new fuel filter, checked the air hoses from the air filter to the throttle body, distributor cap and rotor are approx 12 months old.
My Bosch Jetronic computer is numbered 0 280 000 556 if that means anything to anyone. My next thought is to replace the O2 sensor as it is original. My Volvo mechanic says the O2 sensors usually aren't the culprit and if they are bad, then I will know it as the car will run poorly. He also tells me that sometimes the fuel pumps both in-tank and in-line can be problems especially if the tank is low on fuel and on wet damp days. I have never noticed increased problems on low fuel or wet/damp situations. The car normally runs great.
Does anyone out there have any other suggestions or ideas?

Thanks,
Luke
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89 244 195K+, 93 944 85K+