I have an ’10 MN which I’ve had since new and done ~260k km. in the last 12 months I have had intermittent issues with the engine running rough, black smoke, low power, bad surging (especially on the freeway) and eventually got a check engine light and went into limp mode. I took the car to multiple mechanics, none of whom could get to the root cause.
Through this forum and other online information I have been able to get to the bottom of the issues. It was actually three problems which, combined with their intermittent nature, made diagnosis more difficult.
1) Check engine light was a VGT Turbo code. The cause was a blocked vacuum hose from the inlet manifold to the turbo sensor/switch. I replaced this with a section of fuel line – problem solved.
2) The rough idle/running was solved by cleaning out the EGR and inlet manifold. It was a cow of a job (especially those two nuts at the firewall) but I cleaned it out with oven cleaner and removed an unbelievable amount of crap. No more rough running.
3) The surging was the Suction Control Valve (SCV). I spun it 180 degrees and it solved the problem for a while and I ended up ordering a after market part from eBay for a hundred bucks. Surging immediately solved.
I am no mechanic but I hope this information helps someone else with MN 2.5D issues. The old girl is only used to launch the boat at our local ramp these days and I hope to get a few more years out of her.
Iain