SChema

I have a 1988 TurboII S4, mostly stock with Greddy BOV, Boost Controller, and Mild Streetport. Air pump has been removed.

I've been doing some research and have found some other people suffering similar problems that I have been suffering.

I'm having trouble getting the car to rev. The car idles all day long at about 1500 RPM (getting that lowered soon, waiting to fix this problem first); however, once I give it throttle, the motor either revs to about 2000 RPM and hangs or the RPMs would drop below 1000 RPM gradually.

In the past, the car would rev to 6000 - 6500 RPM just fine in neutral, with a load the revs are limited to about 5500 RPM. Gradually, the symptoms got worse, revs were then limited to about 4500 RPM, then 3000 RPM and to the present day of about 2000 RPM.

I have a new fuel filter and air filter installed. Both primary and secondary injectors were cleaned and flowed.

I've checked the AFM and TPS and both resistance readings fell within Mazda specs.

Checked for vacuum leaks and found none. Double checked all of my wiring for loose connections and frayed wires and found none.

Doing some more tests, hopefully by tomorrow. Planning on checking fuel pressure and compression.

I'm also curious if an ECU going bad could cause my Acceleration symptoms to gradually go bad?

Any help in finding a solution is greatly appreciated. Thanks in advance!!!