Hi Folks,

So I bought a Mazda 6 TS 2009, 2.0L diesel about 4 months ago. Everything was working fine until about a month ago, the car started losing power while driving. It wouldn't have any boost when you put the foot down on gas, and after a few seconds it would then have boost and work fine, but then when the car slows again it takes a while for the revs to build up. When the boost does kick in, sometimes there's black smoke from the exhaust.

So I've been taking the car to the local garage (it's a very reputable one with good reviews) and they've been trying to fix it for a month. First they told me the intercooler is damaged, so I replaced that (I could see some cracks in it), and the car then drove fine for about 40 miles on the motorway but the problem came back. Then they checked again and said the turbocharger's wastegate is stuck and doesn't move so that could be the problem. So I managed to get a reconditioned turbo and got that replaced. Again fine for about 70-80 miles and it started losing power again .

The problem seemed to get worse because I now couldn't move off from stationary as the revs just don't go up for about 10 seconds, then a massive boost. The revs also started going up and down very slightly while idling and you can hear the engine revving in an oscillating pattern.

All this time, if I turn the engine off for a few minutes, it would work fine again for a few miles until it starts losing power again.

So took it back to the garage, they were baffled as well and checked all sorts of sensors like MAF etc. and couldn't find anything. They replaced the fuel filter which made no difference. Then they suspected it might be the EGR valve so they blocked that off. Again the car was fine for about 40 miles on the motorway and about 10 on normal roads (at which point I thought the car is fine) . I turned the car off for couple of hours and started driving again and to my disappointment, the problem was back.

Took it back to the garage and they said they've done everything they could and didn't wanna spend much more time on it.

There are no error codes at all, not even in the history log. I checked with my own OBD2 reader as well.

So my question is, what could be the problem? I just want to get rid of this car tbh and buy a new one, but obviously can't sell it like this. Sometimes it would drive fine for about half an hour with no problems at all.

Apologies for the long read but I really don't know where else to go for help! Thanks in advance!