Ok, I've come to some conclusions about my idle problem on the 86 740 Turbo. Being a mechanical engineer, I hooked up the wiring wrong (interchanged throttle switch & idle air control valve connectors) after a major wire harness re-build. I discovered this by running thru the trouble-shooting procedures in the Volvo green manual for the B230FT engine.

After checking everything else by the manual with no problems found, I decided to open up the FI computer and take a look. Damn - burnt out one of the circuits (terminal 10), one leading to the idle motor. I repaired this with a jumper wire, but still no idle control.

Anyway, I think I have also burnt out what looks like a transistor or mosfet in the same circuit of the computer. The transistor/mosfet has the wording "BDX77" on it and also the number "28609" (which could be a date....as the car is an 86 model).

What are my chances of finding a direct replacement component that I can solder into the circuit board? Anybody know what this component is based on the above quoted codes?

Thanks!

Greg

Try a Google search on "BDX77". It shows several hits on this transistor

number. You might be able to get the specs and substitute something from

Radio Shack.

Gosh, why aren't all our electrical engineers responding to your "Geek" call? Hmmm. I know I'm not the former, hopefully not the latter, so I'll tell you what I know.

Part numbers on ECU components are difficult if not impossble to cross reference. That part was likely supplied by STMicroelectronics (or others) by special order to ECU manufacturer requirements (Bosch, Luxor etc). The part number will typically be a Bosch private or "house" part number stamped on their closest available component. Information on house parts is generally not in the public domain. Somebody who really knows their stuff may be able to deduce what it likely is. Unless you're planning on repairing these for a living, the most expedient approach is to get a used one from a bone yard or off eBay.

For more information on ECU failures for 740 turbos of your vintage you might be interested in this UK Volvo Club page.

Remember though that European spec' 760 Turbos tend to have motronic injection, and don't run oxygen sensors for that age of car.

Regards