I've owned my 1991SE 940 (turbo) since Nov. 2004. It has 175k mi. About 2 months ago, the car would not start. It would crank, make spark, but wouldn't start. I replaced the ignition coil, wrapped on the relay bank, checked the electrical connectors, and eventually got it to start.

This happended on and off for about a month. When it wouldn't start, I'd give a couple strategic whacks to the relay bank (near the passangers left foot) and it would start again. Figured the fuel pump relay was bad (BTW for other SE owners, it's green, the original had a 'B' printed on it, and is about $42).
After the new relay, all was well for about a month, so I thought all was fixed.

Yesterday, I was trying to figure out a bad idle (in retrospect, probably related to a bad ECU). I started the car - it idled for about 30sec. at 750 rpm, then dropped to 500 for about 3 minutes, then below 500, then stalled. Tried to start it again, and I'm back to same symptoms of a couple months ago. It cranks, it sparks, but no voltage to the fuel pump (I checked with my meter).

The relay is new, the ignition coil is new. Like I said, the idle has been rough for quite some time. Other than that, the car runs well. There are a lot of squeaks and rattles in the cabin, the carpet smells a little funky, but I won't blame the ECU on those.

But I do think a lot of fingers are pointed at the ECU for my drivability issues. Any thoughts? Should I buy a new ECU? Where is it located, exactly?

Thanks.