In need of assistance regarding my turbo
hi, iv been an alfa owner for quite some time now, started with a 156 which had insane immobiliser issues but loved it personality, and have recently upgraded to a 159 1.9 jtdm. iv noticed only a few weeks ago however that very occasionally in 5th or 6th gear my mpg drastically drops and if i release the throttle my turbo pressure disappears in an instant. i assume this is a problem with my turbo since there is usually a small bit of pressure left once i release the throttle and it gradually reduces to 0, the turbo will return to normal once i switch off the engine and restart. iv also been informed when it occurs, small amounts of black smoke is being released through the exhaust, although i cant confirm this.
I thought it may have been split pipes but other threads seem to suggest that and error message would be displayed if that was the case, im really stumped by this and would appreciate any help
thanks in advance if i dont get bak to you