When I accelerate under load .I can hear a hissing noise from under the bonnet . . I have had the E G R valve changed as the old one had the pipe from the e g r valve disconnect from the engine when put i it back on i smoked bad under the bonnet . Changed the valve put the pipe on No smoke as don’t pull well under load hop this makes sense
Running Rough, Starting & Power Loss
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Could be a choked exhaust / cat convertor .
your hissing noise is probably loss of air from an intake pipe