Gents

Ever since I have owned MB 27 it has had a slight hesitation when you press the accelerator pedal. Not much but annoying. Usual suspects were renewed, potentiometer and idle vale. It had a full Crypton tune using an old Ford plug in diagnostic box of tricks. New leads, coil, plugs distributer cap etc etc. That was 4 years ago.

When we went to Gatcombe Park the other month the idle speed started to play up. So everything was greased. New potentiometer and idle valve again. Spoke with Nigel at QRG and he suggested what I had already done. He had known of this problem before and he said it must be an air/vacium leak. So I replaced all the hoses that I could think off. Nigel suggested firing the engine up and then spraying cold start where there could possible be an air leak. If there was one where I sprayed, it would make the engine speed up. So it was liberally sprayed to no effect. I even took the top of the air filter box off, no change. Un plug the lead to the idle valve and it settled down.

I then thought it might be mechanical friction within the throttle body. I took all this apart and oiled the spindle in various places. I was just putting it back together when I noticed that the gasket was 75% covering the hole between the two halves of the throttle body in the top left corner as you look at the picture ie just below the left hand one of the three bolts. There is a bulge on the left of the body ( in the ally casing) that allows air to get at the idle valve more or less direct from the black air hose. Acts like a chimney. So the gasket had reduced this air flow to about 25%. I trimmed it off internally and fitted it all back together. It immediately cured the variable tick-over and the Brucie bonus was that it also cured the hesitation. It is now smoother under heavy acceleration as well. The cure took some finding and was by accident really.

Pete Humphries MB 27



Thanks very much for this brilliant tip and well done for finding the fault.

Mick G ;o)