Very High Tickover

[melinx]

This morning I decided that it was time the Carlton had a run out to a local Sunday market; it was a bit cool (5C) but fine and dry.

Even after the engine was fully warm the tickover speed wouldn't drop below 1500/2000 RPM.

I thought 'sod it, the temperature sensor is nackered' because it was reading 0.7 gph instantaneous instead of the normal 0.3 at 650 RPM, so I assumed that it was holding fully rich.

Checking the CTS showed that it was 195 Ohms which is correct for 90 C coolant temperature !

'Ah' I thought, 'the ICV is sticking' so I changed it for my nice clean lightly oiled spare: No difference whatsoever

Scratching my head and thinking ' what the #*!*' I idly waggled the plug on the AFM and the tickover speed immediately dropped to the normal 650 RPM

Removing the plug and inspecting it showed it to be perfectly clean and the contacts on the plug nicely closed up and everything had a light film of WD40

Much waggling doesn't repeat the fault !

Tricky little suckers these control systems ain't they ?

[Johnny A]

dry solder joint inside the AFM

[melinx]

I've had a look inside my spare AFM which already has the lid unsealed.

Something that slightly concerns me is that there are two connections which feed the ground and +5 Volts to the ceramic 'tile' which has the resistive track for the flap position wiper mounted on it.

The connections to these are two reasonably thick bronze springs which press onto the gold plated connections on the ceramic 'tile'.

These bronze springs are welded to the connector plug pins and it is possible that if there is a problem with these contacts, a slight movement of the plug pin will restore a proper connection

I'm thinking/hoping that a problem with the plug/socket connections is the most likely cause of the problem because I don't want to carry around a bulky AFM spare 'just in case'

[melinx]

This is not my AFM, its a rather good photograph of the earlier version which has the 'carbon monoxide adjuster': This is connected to the blue rectangular potentiometer on the right.

Twiddling this without reference to an emissions meter up your tailpipe can cause great problems

This control is not present on the later versions of the AFM (it's all sorted in the Motronic software which does running adjustments by reference to the Lamda sensor)

Another difference is the later versions have 3 of the spring arms with small studs on the central potentiometer wiper arm instead of the 2 shown here, making them considerably less prone to cause wear on the resistive track.

The bronze spring connectors I referred to in the previous post are virtually central to the plug at the bottom.

[DevonGSi]

I had this on my 24v GSi. Was just a air leak on the rubber bits of the dual ram. New ones sorted it.

Hope you get it sorted.

[melinx]

It is sorted it hasn't recurred since 'waggling' the AFM plug and using a bit of contact cleaner on the contacts just in case