Twin Turbo troubleshooting

[emguajar]

Hi, my 1999 BH5 GTB has been having some issues recently.

First, whenever I start it up, the car struggles to maintain a steady idle throughout the heat cycle. It doesn't shut off, but will consistently alternate between the usual 1500 rpm on a cold start down to about 700-1000, and the exhaust note is dramatically different, almost as if it is down a cylinder.

Second, the car seems to misfire/cut boost throughout the primary turbo. It still accelerates fine and is relatively driveable, but it feels down on power between 2000-3500 rpm; almost as if I am accelerating up a hill or into a headwind, until it hits peak boost on primary during which the car accelerates fine and transitions to secondary as usual. This is especially noticeable in 4th and 5th gear, and maintaining 110km/h on vacuum is difficult and makes highway driving especially uncomfortable. Going through the powerband onto secondary makes this issue less dramatic the next time I accelerate on primary, and the car seems to misfire/cut boost less and feels more confident.

As such, I've started to drive it by accelerating on vacuum until about 3000 rpm, then rolling into it and getting up to speed.

All of this occurs with no check engine light.

I've replaced the spark plugs with NGK BKR7EIX gapped to 8mm, and the stock coilpacks with Napol Performance 22433AA421 2.0 turbo coilpacks. I am running Shell Rotella T6, and a generic apexi cone filter which came on it from japan. I run Petro 94, with no additive on the stock tune, but I intend to get the ProjectLAMBDA tuner.

I have tried to clean the maf, but I've read it is better to just find a replacement, which I have had trouble sourcing.

Anyone encounter a similar issue? Any help would be appreciated, else it will be going into the shop. Thanks!