mystery black box

on my 92 geo tracker i was taking the computer out to swap it with another one to see if it got rid of the miss/surge problem there was a black plastic box screwed to the firewall below the computer. i thought it was a aftermarket car alarm box till i took it out and looked at it. says suzuki and K*H AT9479 and seems to plug into the stock car wiring harness. box is about 6" x 8" x1". seems to run fine with it out of the car, anyone have any ideas?

The only thing i have come up with is that it is a relay of some sort. I know some cars have a relay for the ECM. But I wouldnt of thought disconnecting it would make the car run better.

it has a large printed circut board inside with a large chip, assorted resistors and capacitors and a couple switching transistors

Another thing it may be is the Electronic Brake Control Module. From what Ive seen these are located by the ECM.

it does not have ABS