zeroptzero

Check the pins on the connector going to the map sensor, and the wiring on the connector. There was a recommendation to zip tie the connector onto the map sensor to improve the contact as some S2000's had issues with loose connections. I've got mine zip tied for peace of mind.

I would suspect the wiring before the faulty ECM.

peakpoint

Just tried using a zip per your suggestion. Also tested wire from map sensor and read 3.6v to 3.7v. In neutral from a cool start it will now rev to 5500 RPMs, but the longer the car is on the lower the RPMs go when any load is put on the car.

Thanks so much for your continued suggestions JFUSION! I have only had the car 2 weeks, so I really want to correct the issue and learn a few things in the process.

peakpoint

Looks like the issue was the air injection pump. We took off the hose and now the car revs up fine. For now I'm going to just put something over the hole attached to the intake tubing. Any other suggestions?