This is common. This is due to the long gear ratio allowing the turbo to sit in a certain rpm range much longer than in the shorter 3rd/4th gears. The best way to avoid this is to use the tephra v7 patch which offers independent boost control for each gear.

If I remember right, there are two boost control tables in the stock roms (#1 & #2) and one wS for gears 1-3 and the other was for gears 4-5 bit you can actually adjust the switching point so #1 is for gears 1-4 and #2 is only for 5th gear. It's been a while since it's just more common for users to upgrade to the Tephra v7 patch these days.

 

Thanks Jack! I am familiar with the gear range crossover table. My table is still stock. Looks like I need change it and make a separate 5th gear table. I'm still puzzled by the cold engine boost issue though.

 

Are you ruinning the tephra rom which as the option to set the WGDC below a specific RPM? Maybe thats overriding the other table we were talking about?

 

I have not made the jump to Tephra mod since I've never had a need for the various Tephra options (like NLTS, valet, alt maps, etc).

 

The KNOCK LIGHT feature alone makes it worth the jump. I can't live without it.

 

OT but were there any hassles to switching to the Tephra mod. I mean, I could make an easy switch and leave all the unwanted options disabled, correct? Just cut and paste maps and immobilizer code? What about my Evo X MAP sensor and direct boost control?

 

cold dense air = more boost.

as Jack said, turn the boost down. Most likely you tuned the car in warmer weather, now you need some tweaks for the colder weather to keep everything safe.

 

This is not a weather issue. It occurs in 100 degree weather as well. It is a cold engine issue.

 

Then your boost maps are too aggressive.

 

My boost is perfect once the motor is warm (except for 5th gear as mentioned above).