ok.
there's no easy way to map a 98 to get the best out of a decat exhaust other then a new ecu or a daughter board from esl.
what's probably happening is overboost and fuel cut.
if you can get the boost back under control it should be safe to run without a remap.
To do this you need to increase the size of the hole in the boost restrictor by about 0.1 - 0.2mm.
this brass restrictor is inside the 3mm boost hose that connects to the turbo outlet.
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