The car, 91 turbo 5 speed, acted up again today. I have posted several posts on this but the crux is it won't rev freely over say 3000 rpms. I have changed, the power stage, coil, RSI relays, turbo hoses, fuel filter, rebuilt AMM, FPR, wires are newer bougicord, and plugs and cap and rotor have been done within the last 10k.

The car acted up this morning, it has been about 350 miles and two weeks since this last happened. What was different was when it did this, I pulled over to the side of the road, shut the car down, waited ten seconds and then restarted the car and it ran fine and I drove it the 35 miles into work without incident and it would rev fine up through 5k.

As before the check engine light did not come on. as restarting it fixed the problem, I am guessing that this is electrical? I am planning to swap the ecu with a supposed good 937 that I got off of eBay last week. Does this sound like it could be an ecu issue?, I would assume the ecu is the original 563 (I have only been able to see the Volvo part number on it).

other than an ecu what else is there to check? I have had the fuel pumps checked by a mechanic and both are in spec in terms of the output.

Could this be a bad RPM or knock sensor? My understanding is that a bad FI relay will create a no start but not this.