Throttle Body Adjustment

[92Syncro]

Hello!

I've pulled the throttle body off my bus to give it a good clean and get all that south african dust out of it. It looks to me like it's all really badly adjusted, but wanted to get a second opinion from those who know better than I.

First issue is that my idle switch doesn't close when the throttle is closed, the stepped guide doesn't rotate far enough to engage the switch. Nice easy adjustment but before adjusting the switch I peered into the body and looks to me like the throttle plate is closing too far. It's started to dig a groove in the body. Should the plate close right on top of the vacuum port or am I making that up? The Bently just says to adjust screw so that it's just touching the stop, but that's probably before the plate has dug a groove and closes too far!

Cheers for the help again!

[92Syncro]

Thought I'd follow this up after a few hours of trawling this forum, the samba and even the bently publishers forum. I have come to the following conculsions. First is that my throttle body is fairly well worn but the cost and availability of replacement is scary The second is that air flow around a closed throttle plate is more important than the position of plate in relation to the vacuum port. Third, don't try to second guess "The Bently" when it tells you how something should be adjusted.

[Aidan]

several preloved throttle bodies here, they seem pretty robust generally but obviously poor maintenance can lead to problems, they all have play that I have seen, on an MV it doesn't make much of an issue because the ecu can cope with inlet air leaks but on a DJ it can't compensate and with the vacuum take off in use as well it can cause all sorts of issues

[92Syncro]

Thanks for the reply Aidan. I'm not sure mine is causing me issues just yet. Still in the process of going through and checking a new bus over. I'll bear it in mind for the future though.

C

[California Dreamin]

In my experience it is fairly common to find some 'cutting in' of the butterfly into the throttle body. When worn like this you can 'VERY CAREFULLY' use some very fine wet n dry paper (very fine grade) to take out & smooth the groove. Thinners is best to thoroughly clean all signs of carbon.
As for the the adjustment...this is where it becomes interesting! in theory you adjust the throttle body so the butterfly is just off touching the housing internally...in practice...the pull on the butterfly through 'vacuum' and 'return spring' tension, tends to make the butterfly stick. It is at this point you 'fine tune on the go' with tiny adjustments to the stop, to the point that the throttle doesn't have the tendency to 'stick/cut' into the throttle body.
This sticking is exaggerated by pivot wear, which allows the butterfly to move more than it should.

So in brief..the optimum adjustment is finding a point at which the butterfly valve is just off the point of 'cutting in' to the throttle body...and the 'final adjustment' will probably need doing with the engine hot and after several road tests.

Martin

[92Syncro]

Thanks Martin, that's some useful information there. I'll heed advice and give it a gentle sanding to smooth out the groove and adjust further when in situ. I'm learning a lot from this forum already and I've not even got the bus on the road yet!