High idle question

my car goes to 2K first coupe seconds then settles to 900-1k after that.

 

I had an occasional startup issue; ended up I ran with the cold start disconnected for a long while, that seemed to sort issues.

Never had an over revving issue (plenty of others!!!) after. Changed out injectors and seals and cleaned / flushed fuel lines and system, that made a massive difference to smooth running.


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Check the gas cable is not snagging on the carpets, also get some wd 40 and spray the moving quadrant just behind the big alloy air inlet on top of the engine.
It can stick and the spring does not close it fully at times.

 

mine is just the opposite. It high idles at about 2K RPM for a couple of minutes, then drops to about 900-1000.

Check the cold start valve - it's that thing sticking out of the right side of the plenum. It may be sticking open and feeding extra fuel into the intake. If you need a new one, Jags and Volvos of the same era used the same valve.

I think there is also a thermocouple somewhere in the system, that controls the cold-start valve. But, I'm not clear on that one.

Sid

 

A bad cold start valve will not cause a high idle.

 

I imagine that replacing and cleaning my K Jet injection system and all the linkages had (the) impact.! But nonetheless I had the cold start plug disconnected and that seemed to make it run more consistently.
Somewhere I have a bunch of notes about what the car did and what was the effect of various changes.


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At the advice of several other forum members when I was in Europe with them, I disconnected my cold start injector (The 9th injector) a long time ago and the car starts and runs fine without it.

I live in Florida, so it is not ever really needed.

I understand it can stick and dump extra fuel into the plenum.
Alden

 

one in a million. You have a better chance of being struck by lightning.

It is a far better bet to take out your teeth to avoid cavities.

Starting well with no active injector is usually a sign it is running too rich to begin with.

 

Idle should be high at start-up. Probably your AAV is stuck. That is located under the expansion tank. Cleaning it with WD-40 should fix that. Also, sounds like your throttle is not closing all the way sometimes, as mentioned. Add another throttle return spring to test it. Not the OEM type, but a long soft spring.

https://www.minisport.com/21a839-su-carb-throttle-return-spring-for-single-twin-carbs.html

 

Auxiliary Air Valve. Electric bypass of the throttle plate to allow greater air volume in fuel/air mix.


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http://www.tonybmw.co.uk/Downloads/Bosch_Fuel_Injection.pdf

Just in case people are interested.... may need to cut and paste, rather than click.


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Oh sorry, they didn't go under the coolant tank till '84. Yours should be just to the left of the throttle body. You can see the hoses bypassing the throttle plate. Test by squeezing the rear hose closed, when engine first starts. If squeezing that hose closed doesn't affect the idle, probably that AAV is stuck closed. Maybe driving a bit is jarring the valve open ?

http://images.clickedit.co.uk/6527/64639257.jpg