hey. my brothers big turbo escort has developed an an annoying intermittent problem. it runs smoothly, but at times, its as if there is zero turbo boost even at full acceleration (dead sluggish) and then rev limits at 4000 rpm. then, if you flick ignition off momentarily and back on, it revs out and pulls strong, but acts up in same way after approx 30 secs. wiring has all checked out ok. block connectors on engine loom removed and soldered. cant get flash codes from ecu. car is 92 with ggr stage 3 tune. any help appreciated. thanks