Hi there everyone. My name is Peter and I live in Durban in South Africa. I have had my Cherokee since new. It has 245000 km on the clock and has done extremely well up until a few months ago. Because of the milage I decided to have the turbo reconditioned because it was feeling a little sluggish( Bad move). To cut a long short, it infrequently started showing Turbo underboost when diagnosed for going into limp mode. I have since had to have the engine overhauled because it ran its bearings and had the turbo again reconditioned. The engine and turbo are now sorted but it still intermittently goes into limp mode and diagnosed still as "Turbo Underboost". The system has been pressure checked by a reputable Turbo specialist and all found to be good. All the Turbo pipes are new. I have also changed the map sensor. We have not changed the actuator are now going to send the turbo back to the specialists to recheck actuator and turbo. Does anyone have any suggestions as to what the problem could be after having done all this work and of course spent a lot of money.
Thank you in advance
Peter

Check all vacuum hoses and connections from brake booster across engine to turbo vacuum modulator valve.
The small plastic vacuum tubes are known for collapsing and / or cracking which causes low vacuum to the turbo vane controls.
This in turn can cause low boost issues as the turbo vanes are not being positioned correctly as being demanded by the ECM.

Some owners like myself have replaced all vacuum tubes/hoses with high quality silicone hose which is impervious to heat and oil exposure. see enclosed picture.
When I did mine, it improved turbo response time!

You should also add a mechanical boost gauge to see exactly what the boost pressure is during acceleration when you are getting the low boost DTCs.
The three known items besides the vacuum & boost hoses that can cause boost control issues are:
MAP sensor,
Vacuum Modulator valve,
Vacuum Solenoid valve. (this valve normally is open or shut, it can also be bypassed, removed from the circuit to test. see diagram)

Silicone Vacuum Hoses:


Vacuum Solenoid Bypassed:

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Thank you for your quick reply to my query. Much appreciated and will let you know how I go.
Regards
Peter