New engine

No I wouldn't describe it as being limp mode I have experienced that in my wifes old T5 2.5 Turbo diesel , mine drives fairly normally just takes a bit of peddling to get it up to speed from stop . It does accelerate but not at a rate that would keep it up with other traffic from lights etc . No sign of smoke , oil consumption around 1 litre every 3 to 4 thousand kays [that's if I remember to check it ] LOL and from what I have read on some posts that's way better than some brand new model VWs which seem to have a high oil consumption rate from factory . We were warned to keep an eye on our new T5.1 oil level when we picked it new from dealer , they even told us with great glee that they had a "Pit Stop" set up at the service dept so if the oil was low you could just pull in and they would top it up WTF !! I will make a booking with Jmac and see what turns up , I do know the joint between the first section of down pipe in the exhaust is fractured so a trip to an exhaust shop is in order , I wonder if that may be affecting the O2 sensor which is just down a bit further from memory . it makes a sort of whistling sound on acceleration . I wished I had put a turbo on the van when I discovered ten years ago that it was no where near the performer of the T4,s 2.5 petrol which was in my old work van back then , that engine was a real goer a certain hill near home has a small sort of lump part way up and it would lift the front pass side wheel off the ground and chirp the tyre this one just rolls over with very little enthusiasm Sob sob .

As others have said, start with the basics.

The first thing I'd do is assess how much unnecessary stuff you are carting about. I know a lot of the 4WD guys add 999kg of accessories & then wonder why the truck isn't overtaking like when it was new.

Check off the general service list of plugs, air filter, fuel filter, clean oil, etc.

Get the exhaust fixed

Get a wet and dry compression test done

Get the codes scanned (there might be some that haven't triggered a CEL yet)

Run 98 ALL THE TIME! Occasional tanks will do nothing for you.

Put a few bottles of Wynns Complete Fuel System cleaner through it.

when was the last timing belt service ???? did you notice power decrease after the timing belt service ? only has to be out a poofteenth to affect off line performance,,,exhaust leak...a probable cause depending where the leak is ??? as suggested upper cylinder additives ...seen 660k on a petrol 2.0 T5 record on a T4 2.0 1.1 million km's.....rebuild is a last resort .

The belt has been done every 100000 approx. give or take a few thou , Jmac has done the job each time and its been perfect . I only sort of realised over the last 12 months that it is a bit sluggish . When Jmac does the next service I will get him to do the belt and water pump as it will only be short a few thou of the scheduled date . The leak in the exhaust is something I will get sorted before the service so it wont give any false signals when its on Jmacs laptop . The funny thing was the last time Jim did the service I asked him about the plugs and I had no idea when they were last done so he fitted new ones , when I picked the van up he showed me the old ones which were burnt right down and expressed surprise the van was actually running at all . As for load carrying the weight I carry never changes more than ten or fifteen kilos all the tooling etc has been in there from day one it's only what I take for individual jobs and that's never more than 40 kg .

Exhaust leak before the O2 is huge
It will throw everything out , more at low revs (ie trying to pick up)
Do that ASAP
Suggest you get support data, maybe do a 0-80 or 100 time, fix it then after 200km do it again

Thanks for that Notso I will see the exhaust shop later today .

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Originally Posted by Sunny43.5

Thanks for that Notso I will see the exhaust shop later today .

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How often did you change the engine oil and the oil filter?

If one spark plug failed, just 17,000km after replacing the spark plugs, was it oily full of deposit? If yes, then definitely have the compression and the cylinder leak down tests done before you replace the engine. The life of the 4 cylinder petrol engines is usually somewhere around 250,000km, though is not uncommon to get much more than that if we'll maintained.

Hi Transporter the lead failed not the plug considering how burnt down they were they were still dry and clean , Jimmy had done the service with new plugs and three days later I stopped at a mates place got back into the van and it was only running on 3 cylinders !! I popped into Jim's place on the way home and he told me that the new plugs would cause the lead to just fail without warning , by 5 pm I had new leads and it was fixed [bugger of a job to feed them under the intake manifold , I'll bet some German engineer laughed at that one ] It gets serviced every 15000 give or take a few thou , read here whenever I remember to book with Jim . I dropped in to a place that does mechanical and specialist exhaust work today , I did a sunroof for his daughter a couple of years ago and he did a brilliant job on my sons Astra last year . Anyway he also said that the fracture would be sucking air and screwing up the o2 readings which in turn would screw up the fuel air mix , and as has happened he said it would trigger an engine fault light . Now in hindsight that makes sense as the leaky pipe engine light and poor performance all started around the same time so that may be it !! . I noticed a sort of whistling sound some time back and never gave it much thought {stereo too loud to hear it anyway } The engine light I put down to some dud fuel as it seemed to come and go but now its a permanent decoration in the cluster . Monday will have the pipe fixed and then to Jim's for timing belt and pump and service check up , its a bit early for the belt etc but I may as well not bother with waiting until 300000 .

Time for some yahoo noises from this happy camper , van was at the exhaust shop today to have the crack in the exhaust welded . When they removed the cat converter the problem became very clear the crack was in the heat shield not the main pipe but on inspection we found the flexi pipe was disintegrating internally and the metallic parts had shot down into the ceramic part of the cat causing that to block and break down . So VW did not get anymore money from me for this one as the exhaust shop rang for a price on the new parts $2400 for the cat plus add the insult they wanted MY old one back or an extra $485 would be charged . So as I knew the bloke at the exhaust shop well he was able to find a second hand cat $140 plus $120 for the flexi and $50 for the EGR pipe so all up with labour job completed for $320 . Result the van has got its mumbo back again acceleration is up by approx. 10% to 15% and open highway you can feel the slight push when I stab the throttle to overtake gets from 100 kay to 120 in just a few seconds . Now just need to get Jmac to do its 300000 service and all should be well again . Whilst I have been down this road with VW and their wanting my old parts back , I believe its a rip off . I own the van and every single nut and bolt on it what right do VW have in wanting to charge $485 extra if they don't get what is legally mine , and the price quoted was for the part trade it did not included the return part price they just wanted a second bite of the cherry .

They offered you an exchange part, which is cheaper.

My guess, is the outright cost of a brand new cat from VW would've been $2,885.