i had just purchased a 91 honda crx with a b16a motor. when i start the car it will run decent then after a while when im in 4 gear at about 2000 rpms the car starts to surge. the guy i bought it from said it was a second o2 sensor which he had installed but still surges. does any one know what might be causing the problem. and with this motor what would be a good ecu upgrade as in new?