Inlet Port shutoff Motor/Mass air flow sensor

First off, get either a matey with a OBDII reader to plug it in, or get a garage to scan it and give you a readout for what's precisely wrong. The MAF is generally really easy - pop off the electric plug and loosen off the big tubes on either side and it'll come right out. They're usually right behind the air filter. The 'inlet port shutoff' sounds like the flap that closes off the help shut down the engine when you pull out the key (but don't quote me on that) so that should be on top of the engine somewhere in between the MAF and the inlet manifold (where the inlet pipe splits into four to feed each cylinder), and again should be fairly easy to get at after you've removed the plastic panels on top of the engine. You should be able to find guides online if you Google the model of vehicle and the parts you want to change. If you're having electrical problems caused by oil or water it might also be worth pulling off the plugs of each affected item and giving each side a squirt of electrical cleaner before plugging them back in before you go actually removing the parts.

The inlet port shutoff is something to do with the turbo. The faults could all be related though. I've seen a few theories that somebody has either steam cleaned it, or oil's got into the motor and caused the others. Readout is below. Apparently it's possible to simply remove the IPSM and set the valves to open for reliability/performance gain, putting a resister where is was so the ECU doesn't sense a fault: http://forums.mercedesclub.org.uk/showthread.php?t=97061

As for diagnostics, best to replace the MAF first and see if the other faults go away? Then go for a delete of the IPSM if it doesn't fix it? I assume removing that would be declarable on insurance? Whilst I'm at it, is it worth replacing the inlet manifold?

Thanks!

edit: http://imgur.com/vETslgt - diagnostic

If you're savvy enough to manage model-specific research, you should be able to find out all the information you need to manage doing these things yourself. Both mentioned items should be on or near the top of the engine so shouldn't be hard to access with some basic tools. I wouldn't bother telling your insurance about anything you do unless it's blatantly obvious it's been modified when you open the bonnet. I wouldn't bother replacing the inlet manifold unless it's either sooted up/damaged, or you want to install a ported or performance one. Other than that the standard one will be fine.

Pick up some MAF cleaner and use that to clean your MAF and the electrical connection to it. They cost a pretty penny to simply replace if there's no need.

Bear in mind that removing the motor and setting the flaps to performance will have a corresponding effect on fuel consumption

Having had a quick look at the link, it looks like you've got a diesel. If you can get the inlet manifold off, have a look inside and see how gunked up it is with black soot. If it's bad, clean it all out (not while attached to the engine!). You should see an improvement in both power and economy if the sooting was bad enough before. While you're fiddling with the IPSM and inlet manifold, look up an EGR delete/disable. Getting rid of the EGR will prevent problems with the IPSM and inlet manifold clogging up in future. I deleted my EGR and would never look back now.

Thanks for this I'll be taking it to a specialist to do the jobs I think, as it's pretty complex for me. I'm ok with the theory, not so good with complex wiring.

The EGR disable job looks much like the IPSM job to me. It's all monitored by the ECU/MAF so needs wiring in a similar way [adding resistors etc] to not trigger limp mode: http://forums.mercedesclub.org.uk/showthread.php?t=68928 (would that be obvious for insurance? Looks under the bonnet wiring to me!)

Am I going in the right direction here?

I'd say you were! Modern diesels are very complicated and anything to simplify the engine bay is usually good - both in terms of reliability and often in economy too. These systems often work well when brand new but a hundred thousand miles or so down the line when things are wearing out a little and clogged up with soot then they'd often detrimental to performance and economy. So long as you don't go shouting from the rooftops that you've gone done modded your engine, I can't imagine the insurance company will care so long as your engine bay isn't full of anodised tubes and flashy lights. All they'll do after an accident, if at all, is take a perfunctory look under the bonnet to make sure you've not gone and swapped a V8 into it or something and call it a day.

On my 90's mk3 Golf TDI the extent of my engine mods are an EGR delete, and the replacement of the injectors for ones which just so happened to come out of a mk4 with 20bhp more than mine, which gives it a bit more pep around town and when loaded down with a full boot and loaded trailer.

I'd say you were! Modern diesels are very complicated and anything to simplify the engine bay is usually good - both in terms of reliability and often in economy too. These systems often work well when brand new but a hundred thousand miles or so down the line when things are wearing out a little and clogged up with soot then they'd often detrimental to performance and economy. So long as you don't go shouting from the rooftops that you've gone done modded your engine, I can't imagine the insurance company will care so long as your engine bay isn't full of anodised tubes and flashy lights. All they'll do after an accident, if at all, is take a perfunctory look under the bonnet to make sure you've not gone and swapped a V8 into it or something and call it a day.

On my 90's mk3 Golf TDI the extent of my engine mods are an EGR delete, and the replacement of the injectors for ones which just so happened to come out of a mk4 with 20bhp more than mine, which gives it a bit more pep around town and when loaded down with a full boot and loaded trailer.

hello can you please let me know where you go to fix the problem as I have my cls with same issueintet port shut off motor on diagnostic today at Saphire mercedes harrowthey said it takes 4 30 hour to work on it and cost arround 430 quid😳can someone helping me at this point NufflesI really appreciate it 🤗