Might be simple. Try the EGR valve, turbo to intake. Elsewhere in this site is a good diagnostic trick: But if you can't find it..... Find a BB or ball bearing a bit larger than the vacuum connector to the EGR valve. (not so small that it fits too loosely or it will suck upstream, not good)) Pull the hose, insert BB -- has to be a snug fit. Re-install hose to EGR. Drive car. Is the lost power over with and good acceleration back plus little or no smoke? Good....your problem is a stuck EGR valve dumping unburned fuel back into intake, an over-rich mixture not burning completely (black smoke) resulting in big reduction in power pulses and not correctable at the ALDA. Permanent repair is to replace EGR valve or, if your conscience allows, leave the BB. (increases NO2 emissions)