I started a new thread yesterday but ironically as I explained my problem I stumbled across the fault but I thought I'd still post anyway. For months now my relay has intermittent "hunting" engine, especially at tick over. If you engage cruise control you can feel the vehicle surging as the power comes and goes. If you stomp on the accelerator your rewarded with a sooty puff of smoke which means these days a MOT failure. It's like it's running rich and those of you out there, like me, might place blame on the EGR valve since there's so much crap circulating around modern diesels. Sometimes, not always, she was a complete bugger to start and I'd get a engine warning light, more often than not she won't start first turn which is unusual. Yep, she rattles away at 140k miles but this is what I found.
As I finished off my original post, post fitting a new EGR valve and then having to refit the thing due to coolant leaks, I noticed a "include file" option at the base of the post and thought a quick video of the thing hunting away might help. Upon switching off the engine I hear the familiar sound of the throttle body closing about 3-4s after ignition off and also a buzzing sound coming from the valve which feeds vacuum to the EGR valve. As the vacuum reduced the buzzing noise faded and went up in frequency. That caught my attention and I pulled off the vacuum hose from the EGR and immediately there was air flowing when it was ticking over, that shouldn't be at tick over. SO... what I'm saying is I was spot on diagnosing the EGR problem, the poor running was due to it sniffing it's own farts but it wasn't the EGR valve, it was the sodding valve. Both items are quite expensive, EGR was £160 (pattern part), £280 for OEM (if memory serves me right) and that valve, which looks like if you open it up it'll be broke forever is £120, on my 2008 it's fitted above the engine behind a metal plate. I've got a 2nd hand one off eBay. After I removed it I could blow/suck air through it, so I guess it's opened and stuck open. Having taken it off I get the engine light but it seems the hunting has gone away, well it did for the 6 mile journey I did this morning. I could of course blank the bloody thing off but then I increase engine temperature, so I'm led to believe. Still, worth checking that valve before you remove the EGR valve, which incidentally is much easier if you remove the heat ex-changer it's bolted onto. The worse part was the lower seal, I opted to leave the lower half bolted to the exhaust where the hex bolts had rusted.