Recent cold weather seems to have badly affected my boost. (STI 5 Type R, decatted with 3" stainless downpipe/exhaust with a standard air box and ITG filter always run on shell/esso super with NF octane booster). The Boost dropped to about 0.6 bar at 5500 revs and the engine sounded a little rough.
I used the ECU re-set on a SECS unit fitted in the car tonight, which has put things back to normal with boost at 1.25 bar max and the engine ticking over smoothly.
There are no fault code readings on the SECS and this has only happened once before, when the car was'nt driven for 3 weeks last summer. I have a horrible feeling it may be a gradual degradation in the MAF sensor.
Grateful for any advice on what the problem might be guys!
If it is the MAF I could also use the part number please if someone has it.

 

Btt.
Any thoughts please anybody; even if its only the MAF part number for a '99 sti 5.

 

Do you have a KnockLink fitted, or did (before you reset it) the SECS report any knock correction?

The ITG filters have been known to contaminate and degrade the MY99-00 original type MAF sensors, so that's something that may be an issue here.

As for the sensor part number, it's 22794AA010. Have you compared the current airflow values as reported by the SECS with previous ones to see if there's any obvious discrepancies/under-reading?

 

Thanks Grease Monkey. The problem would appear to have been fuel related. A switch to a completely fresh tank of Shell super (away from Esso) with the NF seems to sorted the problem.
Everything now back to normal with boost and I will keep an eye on airflow. Thanks again for your help!