My Friend has an ep 91. A problen has evolved in its own.. Once he starts to throttle up its starts backfiring and looses all power. then at certian times it takes all the throttle at once and boost normally. we tried replacing leads , plugs and distributor caps & even map sensor. The only mods are RRFPR and a screamer pipe. apart from that its standard ct9. No fault codes are logged. Any help?