Getting the best idle?

[philwaters]

2.0lt Zetec on TB's + Emerald ECU, Piper cams, etc, so it is always going to be slightly lumpy, but I was thinking about this the other day after finding a method on the FAQ site. The thing that got me thinking was the comment "Look at the lambda scale and adjust the fuelling until it shows two or three bars into the yellow".

With my car I have the lambda around 13.1 - 13.4 at idle - well into the green. Any less fuel and it starts to stumble. I think this is due to not enough air speed and the fuel dropping out.

 

So - what should I do? Open the TB's on the idle screw until it will idle at 1000rpm with a leaner mixture or leave it alone as it seems to work, doesn't give any problems pulling away, etc.. but uses more fuel.

All the engines I know run pretty rich at idle - so I've never questioned it before....

 

Phil Waters

[Myles]

Unless you've got a wideband lambda, the standard readout isn't going to be a huge amount of use - it's little more than a switch (now we're rich / now we're lean) - not really a measuring instrument.

 

I'm sure Oily has published a simple guide as to how to set up TBs for a decent idle - the only bit I can find at the moment is:

 

your throttle is way too far open and the engine is therefore runnoing on the wrong part of the map, close the throttle completely, synchronize the TBs, then open the throttle just a little on the adjustment screw, then align the throttle pot and turn idel control on, once hot use the method I sent you to setup the TBs.

 

You will run rich at idle - partly due to the reasons you've already suggested (low air speed etc.)

 

I would expect you to be able to idle lower than 1krpm if everything is set up correctly - and assuming that you're not running bonkers cams and timing....(?)

 

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[philwaters]

Oily's guide is here and it is that that promted me to question my set-up.

I have a wideband, so I trust the readout.

 

Maybe I'll leave well alone - it is probably pretty much right.

One of the other questioning reasons was that with the throttles almost closed the starter struggles to turn the engine over when it is hot - if I crack the throttle open it will spin over and start...

 

Phil Waters

[millsn]

pretty sure my tickover is 950 rpm Phil. I would imagine with your barn door ports that yours might need to run faster. Battery is fully charged is it?