G'day,
I thought to use my car's correct year and model, I was calling it an '85 240. Anyway, I recently replaced the old poor running K-jet with a better K-jet, the install went well, as per another thread, but she seems to have a really low idle until warm, then runs perfectly.
the cold running injector is getting lots of fuel and squirts wells, the CIS seems alright. When I initially start the car, she gets an idle of around 500 rpm, a rather lumpy idle, once warm, very nice.

I have played around with the fuel mixture screw, it was set a bit rich prior, and is now a healthy side of lean-yet to check the plugs though.

Any thoughts?

Cheers, Gareth
Auxiliary air valve aka warm up regulator is my guess. Attached to cam cover with a hose in & out & a plug on top. Could be crunchy wiring there, couple be it's gummed up, could be it needs adjustment - there's a little lock nut which allows you to open & close it a bit.
I assume you have looked at http://www.k-jet.org/articles/information/k-jet-in-detail/
We recently re-furbed the Kjet on the 242gt, so have been through what you are going thru.
The items that control idle are - Aux air valve and control pressure regulator. the first is always in action, the second only does its thing when that engine is cold. ( acts like a choke after startup )
First thing I would check, is that assuming the Aux air system is clean, there may be missing or loose or blocked vacuum lines that control it. sometimes people work on these and don't know about the aux air valve, so they muck around with the throttle stop. check that the black knob actually is the thing controlling the idle speed.
We had the fuel distributer rebuilt. luckily our control pressure regulator appears to work, but these can also be rebuilt.
we found that the air fuel mixture inside the fuel distributer is very finicky. that is, there is not much difference between run and not run, perhaps one full turn of the allen key. I set ours to as rich as it would go to the point of stall, then backed off a quarter turn. still gets great economy, and runs nice. I set ignition timing a bit more advanced than the recommended 5 degrees ( about 10 now). and we tested by ensuring it revved well but does not ping at all.
not sure what cam you have, but the gt likes to idle at 1000 when warm.
hope some of this helps.
G'day,

Thanks for the great tips, I will have a look today at the aux air valve, and any vacuum hose I might have knocked loose. I have visited the K-jet site and downloaded what I could, great resource!

Did you take photos of when you did your own refurb on the k-jet? It would be great to get pic online...

I will keep you posted,
cheers, Gareth
Scott recently got me to diagnose and repair a similar issue on his '84 GLE, in his case it turned out the aux. air valve wasn't opening very far, and he had a couple of split vac hoses causing minor vac leaks. Some new hose and fitting a used aux. air valve from a good running engine sorted it out.

His ignition timing was also retarded by a few degrees, returning it to the factory setting increased the base idle speed, so I'd recommend checking that if you haven't already.

One of the things that helped me diagnose the issue was that I found I could bring the idle up to a good speed when cold, say 900rpm, by adjusting the air bypass screw on the throttle body. If I did this however, the hot idle was then too high. Adjusting the screw back in for a good hot idle speed, brought it back down too low (500rpm) at cold idle. Because of this behavior, I knew it wasn't getting enough air when cold, therefore I knew the aux. air valve wasn't opening far enough.

The aux. air valve contains a "shutter" which slowly closes as the valve heats up, the shutter is attached to the end of a bi-metallic spring, which flexes and rotates the shutter as it heats up. The primary source of heat for the valve is the engine itself, heat conducts through the valve cover and into the body of the valve, heating the spring.

The wires power a heating element, which provides additional heat to close the valve a bit faster. If the element isn't working, due to an open circuit due to damaged wiring etc, the valve would be more likely to stay open longer, giving a high idle, so I don't think a non functional element/damaged wiring will be an issue in your case.

Note also that the cold start injector is supposed to spray fuel only when the engine is both cranking, and the engine temp. is cold. To do this, the injector gets it's power from a terminal on the starter motor solenoid, via a thermo-time switch (temp. dependant switch, only closed when cold) in the head.

If it's spraying with the engine running, it's wired incorrectly, or it's power wire is shorted to a power source, and the engine will run rich and use a lot of fuel.
Great bit of tech info explained very well there! ^
You are right,
Great write up. I checked the aux valve, it was open a small amount, and was closed once warm. When the car was running I lifted off the hose a touch and the engine raced a fair bit. Since messing with it, the problem appears solved. I took her for a run and was very happy with how she ran, good and strong. Thank god the old k-jet worked well, lot of work getting it in there!

Next I have to tackle the bushes.....

Thanks for the tips guys
Gareth
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