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Evo 9 PnP-Idle Problem (Surging)

Joel Siaw

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Hi all,

After few hit and missed, finally got my car tune today. Everything gone so well, achieving a good target 26 PSI - 390HP.

Everything was good after the last power run complete with road test.

But things turn bad after taking some pictures, the idle start to rev up (idle surge?)

It just happened randomly. I have an AEM wideband AFR which shows it is running lean but when we put the foot down the AFR shows the value again.

Plug back the standard ecu and everything works like the old time, so we think it's the software problem.

Car has the Link 4 Bar MAP Sensor too.

Any thoughts of how to solve the idle problem?

Tuner going to call Link for advice tomorrow.


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It might be a case of some heat soak on the IAT sensor causing it to lean out the mixtures which in turn makes for a lean surge. Idle control will then try to compensate and make it surge more.

The tuner should be able to find the cause with the lap top plugged in while it has the surge.

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Stock ECU behaves just like link does, the difference is how it's setup.

your tuner should be able to easily fix this by tweaking links functions(iat,ect,idle closed loop/open loop,ign idle target etc all play in)

If you disable the afr target and set up idle without corrections and then enable corrections and tweak them as you add them you should be able to get it right.

cheers // Fredrik 

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