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New 3s-gte build - surging idle when cold


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Hi all, we recently managed to fire up our new 3s-gte (installed in a ST185 caged tarmac car). The engine is a pretty standard Gen 2 (as installed in ST185s) engine. Standard compression, standard throttle body and air bypass valve but larger cams (272 from memory). To get it started, we took the tune from our other GT4 (a ST205 with a stock engine that had been tuned by one of the local tuners), altered the I/O to match, and got it going.

However, the idle seems to surge a fair bit when it is cold to the point where it needs a bit of carefully timed throttle to catch it from stalling. I am no expert in tuning, so I'm not really to sure where to start to get get it to have a stable idle. I have attached the tune file - any pointers on where to look would be welcome.

55-Shelley change to 3bar GM map sensor.pclr

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Hi Adam - please find attached (sorry - took me a while to get back to where the car is). It basically started, I had to keep it alive with a few well times stabs at the throttle, and then I let it conk out eventually.

Apologies for the IAT being stuck at 50 degrees - it is a wiring error that I fixed after taking the log.

Please let me know of any areas I should be looking at.


210303-Shelley surging idle PC log.llg

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I think it is mostly ignition related - although with no lambda fuel is completely unknown.  Idle valve position is reasonably stable so it doesnt appear that idle air control is a big contributor.  

Try the attached map.  I have tidied up the ignition table around the idle area, enabled idle ign control and disabled the ECT ign trim.  See if this helps, if not you are going to need a lambda to see what is going on with fuel.

698054618_55-Shelleychangeto3barGMmapsensor idle tweaks.pclr

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Many thanks Adam - I'll give it a go in the next couple of days.

Regarding fuelling, the 'master fuel' in our ST205 tune (that I used as a basis for this) was set to 9msec. Given that this engine is running 720cc injectors (compared to the standard 540cc injectors in the ST205), I also reduced 'master fuel' to 6msec in an effort to compensate. I acknowledge this is a bit of a blunt instrument, but the plan is to get it properly tuned soon anyway. Let me know if you think it may be worth bumping that back up to 9msec.

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