Club 80-90 Forums

Ashwood wrote:Yep, found it, unplugged it and revs went higher. Reconnected and revs dropped to the fast idle in about 5 seconds.

will try the big idle screw next, just turn clockwise?

is the dizzy the distributor? Technical mechanics talk?!

Excellent news on the temp2 test.
Yes, just turn big screw in clockwise to reduce idle speed.
And yep, dizzy is distributor. Soz.

Did you get to check that vacuum hose?

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I’ve turned the big screw 2 half turns and there was a slight reduction in revs. After another quarter turn and the screw stopped, so I took it back a quarter cos wasn’t sure whether it should be screwed to the stop.

how do I check the vacuum hose? Is that the unit next to the dizzy?

I like the name ‘dizzy’, will teach that to my boys who are budding mechanics!

cheers for your continued support.

On the lefthand side of engine bay, you probably have an idle control box.
There's another more complex one behind driver-side tail light too, but let's check the former first. 

So in diagram below, the one on the left labeled 'another stabiliser' there should be two plugs connected into the bottom.

I think you should be able to unplug them, and join them together, effectively removing said unit.

Try that, then start engine and recheck. 

Found the box but cannot work out how the connectors unplug. They’re in a tight spot with one blocked by more wiring. I’ve tried squeezing the outer casing and pulling firmly but they are not budging, and the box it was connected to looked like it wanted to come with it. I’ve only just mastered the other type of wire clip…lol

I’ll have another go tomoz…

the 'Another stabiliser' is actually a digital retarder which retards the signal from the hall sender artificially so it can run even more retarded at idle when hot than the vacuum unit on the dizzy can make it
Check that you have vacuum at idle on the retard side of the vqacuum pull down unit on the dizzy as that vacuum also controls the fuel pressure regulator allowing more fuel to return to the tank and thus lowering the fuel pressure to the injectors.
At idle the vacuum from the plenum chamber is high and the vacuum from the throttle body is low so spark timing is retarded, as revs increase vacuum at throttle body increases (so advancing timing) and the vacuum at the plenum chamber is reduced so fuel pressure rises making more fuel available to the injectors, it is a crude but effective system.
Spraying a bit of brake cleaner or the like around all the vacuum hoses and intake pipes will show up any leaks as the 'fuel' will be drawn into engine and revs will rise slightly
DJ's do not like air leaks on the intake side as they have no way of metering them and it messes with the fixed calculation of fuelling for the air/temp/timing which the map is built on

Managed to disconnect the leads from the digital stabiliser, they were chuffing tight and took a lot of patience! Connected them together, fired up the bus, but she was still idling fast once warmed up.

I’ve noticed one of the vacuum pipes by the dizzy is easy to pull off, so wondering if there is a leak. I have some brake cleaner/anti squeak stuff for the bikes, presume that’s would be suitable to spray to detect a leak?

Unit behind RHS rear light, hmmm, not sure how I get to that…

take the light off, access isn't great

have you tested the switch on the throttle body for switching and continuity at idle, if the switch isn't working correctly then the idle control unit isn't running the engine, the ECU still is.....

I’ve put the tester across the throttle switch connector (same location as smiffos pic above) and got no reading on resistance. Haynes manual stated 1.5 or less on idle and full throttle and infinite in between, but I got nowt! I was going to attach a pic showing where I tested but cannot find how I attach a pic…doh. Could the switch be the issue I have got affecting idling?

I tested the end with red sticker on it. Was that the correct connector to test?

Wait for someone else to confirm, but yes, I think that's it.
I'm sure you should be able to loop out the terminal back into the loom from there too, which in my simpleton mind, should make the ECU think the switch is active?

If idle normalises, then it's deffo just the switch. ( Or adjustment of said switch. )

Wait for one of the old timers / experienced ones to advise though. I don't want to suggest something that could make it worse before they nod it through! 

yes the white 2 pin plug that is fixed to the intake pipe; you should be able to hear the click of the microswitch with the engine off and testing across the two pins in the plug you should get continuity when it switches at idle, then open circuit as you open the throttle and then continuity again at fully open throttle

Aidan wrote:yes the white 2 pin plug that is fixed to the intake pipe; you should be able to hear the click of the microswitch with the engine off and testing across the two pins in the plug you should get continuity when it switches at idle, then open circuit as you open the throttle and then continuity again at fully open throttle

^^WHS^^
+ you can see if it makes a difference by using a piece of wire to short across the two pins in the corresponding plug to the ECU. This mimicks closed switch at idle and should bring idle speed down noticeably.

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Dusted the tester down again, no continuity at the switch on idle or full throttle. Looks like this could be the bad boy! How do I replace this switch

will try and short wires to ECU next - where is the ECU? - it’s a good learning curve for me…

cheers.