Wierd thing that happens

[bigtim]

dump valve maybe

[umpkin]

cant see why that would make a difference at what speed im doing??? it idles fine anything below 60mph and my DV is a baily twin piston gp1.

[PukkaSilvia]

Ive had this on my et and det. Have you got any exhasut blows or as tim says a dump valve fitted. Sometimes a faulty or wrong specced dump valve can cause the problem.

Give the old girl a good old service mate and check sensor plug contacts, boost hoses are all good and tight ,Also listen for hissing around the inlet at idle too(vaccum leak)

[adzs12]

Sounds to me like a vacuum leak.

[30psi]

Throttle position sensor.

[umpkin]

but all those would also make it not idle when at a junction, in normal driving it idles fine, its ONLY when the car is moving at more than 60+mph and i slip it into neutral. the only think i can think of is the amount of air being pushed into the front of the car at speed is forcing to air into the intake.