Rattling noise from TVIS area

[Tiger Tim]

Hi All,

Hope there are still a few knowledgeable people keeping an eye in this forum. I've noticed the last few times that I've taken my MK1A out that there is a loud rattling type noise when I leave off the throttle. Not there when driving normally or at startup. Seems just to happen when coming up to roundabouts or stopping. Had a look today when stationary with the engine running. Appears to be coming from the TVIS area. If I increase the throttle speed & leave it go the noise just happens slightly before the engine comes down to idle speed. Is it possible it could be from the air control butterfly valves as it appears to be from that area. I've heard of people removing them entirely. Any way of isolating them to prove that they are causing the issue before I take off the manifold?.

T.

[jimi]

If you take the vacuum line off the actuator (blank the line) the butterflies will stay open. Normal operation is
Engine off = v/v's open
Engine running ( below T-VIS actuation rpm = v/v's closed)
Above actuation rpm = v/v's open ( until rpm drop below a set value)
Operating points for T-VIS are
MK1a it comes in at 4350rpm and stays in until the revs fall back below 3950rpm.
MK1b it comes in at 4650rpm and stays in until the revs fall back below 4250rpm
The butterflies are held on the spindle by screws I have heard of them coming slack and causing a rattling noise.
I wouldn't remove them on a standard engine, you'll lose torque at lower rpm and there's little enough as it is.

[Tiger Tim]

Thanks Jimi. Much appreciated. Going to disconnect the vacuum line & see if the rattle disappears.

T.