1993 940 non turbo with 290K miles, with pulse-air system. I replaced the original head with a rebuilt head because the original head had a cracked exhaust port. The replacement head did not have pulse-air ports so I did not reinstall the pulse-air manifold, and I plugged the pulse-air vacuum control line from the controller. The car runs and drives well and idles smoothly. I'm pleased with how it performs, except that it's dropped 2-3 miles per gallon. I'm getting about 19-20 miles per gallon now whereas before I was getting about 22-23. There are no fault codes in the ECU.

From what I've read about the pulse-air system it's mainly to reduce emissions. I've not read anything about it improving fuel economy, so I'm assuming my loss in fuel economy is due to something different about the replacement head other than the fact that it's not equipped for pulse-air. If I've lost the fuel economy for good, that's okay because the car is performing well otherwise. However, if I could recover the 2-3 miles per gallon by retrofitting my replacement head with my original pulse air manifold I would consider doing that. I no longer have the original head as I scrapped it. I've driven the car 3K-5K miles since replacing the head.