Hey guys I've been lurking for a couple of months since I got my 90 rx. 110k on the dash and runs strong. I've been working on getting the auxiliary ports to open by seafoaming the engine twice and Pb blastung the actuator rods. I got one working and now about a week later I am getting stuck in limp mode randomly. It doesn't occur only at WOT. But it seems to happen about 5 minutes into driving when the engine warms up and happens 3 to 5 times in a row (restarting the car in between to fix it.) Then it runs like a champ again. I pulled a code 27 (mop) and a couple other codes I had trouble reading (will look into it tomorrow.) I think it could be a bad ground or a clogged cat from seafoam. Please help! It's my dd and im 17 with 2 cools and a job

 

Typical Limp Mode caused by the electric OMP.
S5's are notorious for that.I always say Mazda dropped the ball on that by changing the mechanical omp to Electric..86-88 had mechanical omp..89-91 went to electric Omp.
There are tons of write ups on this subject so it will show up frequently if you type it into search.
I can't give you specific info as there are different scenarios.
The Ecu can be effected though,so Try to attend to it or you are looking at an ECU replacement too.

Now,although you Cannot Remove the OMP on an s5 completely with the Stock Ecu,you can Look into an alternative that will allow you to do so,and that is the RTEK ECU,whic is a Chip put in your Stock ECU to allow to to remove the OMP,..BUT you will have to Premix your fuel with 2 stroke oil to lube the Internals.
Look up "Premix" too!