1993 Volvo 240 L4-2.3L SOHC VIN 88 B230F (Federal nonCalifornia)

Symptom: Stumble for up to 40-50 seconds at idle or light acceleration after cold start. I can interrupt the problem by throttling a little harder and within 5-10 seconds the symptoms disappear.

Forum research has revealed that the most likely cause is the need to install an EPROM kit into the ECU (currently have BOSCH 0 280 000 951 / Volvo 6 842 115). All Data DIY states that the kit is # 271836-9.

Need a recommendation on where to get this kit? I'm willing to go to a dealer but it's been hit or miss on "customer service oriented parts folks. And of course I'm looking for less expensive but not "cheap".

Other thoughts are most appreciated.

Previous mechanical efforts leading up to this:
big tuneup (was needed anyway), cleaned all electrical contacts and grounds, confirmed eng temp sender resistances, MAF part number is correct and tests okay as does the throttle position sensor, O2 sensor checks okay (although at cold start it is ignored), IAC and throttle body cleaned and are functional, connections at the computers are clean, ran full OBD with no codes, no codes during stumble.

S,
J.R.