I have a 2000 S320 cdi, 120k miles with FSH, chipped last 2 years. Recently, there has been an intermittant lack of power (usually once warmed up).Approx 1/2 power. I have changed the MAF sensor (no difference). black smoke on hard acceleration. Diagnostics dont indicate any problems. I have changed air filter and checked all basics. I am wondering if (God forbid!) it could be the turbo. can anyone help please