ORIGINAL: Jack28
I also have problems. I have a Wren 44 gold ,on board start version in a Savex L-39, I just maidened it about a month ago, and I now have 8 flights on it. From the very begining on a test stand , Brand new, the Engine was unsteady at idle I would accellerate fine but after running it up and returning to idle the rpms were 65K at idle. I e-mailed wren and Sara had me Set the stability delay to 10 and then run the engine up and down several times slowly, then shut it down and set the stability back to the standard 30 setting. This seemed to work and the next run was fine. After installing it in the plane the first flight was good and the idle after landing was 62-63k .I thought it to be a little high, Sara said it thakes the Ecu time to learn the idle. I have just put 4 flights on it on monday night,the first flight it flamed out on the first fast pass, it made a loud swoshing noise, I thought the tailpipe came out. I dead stick landed it fine and, rechecked it, everything was fine. I then refueled and flew it 3 more flights, each flight the rpms at Idle were getting higher and higher, the last flight the rpms were 91,000, This is way too high . I need to try and get this fixed or send the complete engine back to Wren, I only have flown it 8 total flights, I am hoping this can be rectified without sending it back, Thanks Jack George.
all in all i think you have a fuel issue
the ecu is self learning , i think there has been or there is something changing in your fuel system
the ecu uses the resistance of the pump to measure the pump voltage.
now if you pump has to work hard to get to idle the ecu sets the voltage higher to get to this.
now if in your flight something changes or has less resistance the ecu needs time also to learn the new curve.(stability delay)
and you have a higher idle.
now since you almost never fly idle in flight ,but just on landing this is when you notice the idle has gone up.
please check your fuel system i think you are using eather to long lines , to many tanks , thin plumbing or something else.
and dont worry we had similair problems with the bigger turbines , we use the same ecu.
and always we could trace it back to the fuel system.