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Shaky engine at cold start

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I installed and tuned a DIYPNP ecu in a turbo miata (95), the engine is very shaky on cold start - much better on worm start.

AFR is ok at 13:1 during cold start.

Other cars I tuned (same car and same ecu) does not have this problem - is it some king of mechanical imbalance ?

What could it be ?

I have a log and the tune file

Thanks !

Target a richer mixture at startup, and taper it off. Some cars just arent efficiently atomizing the fuel when they are cold.

You could also try increasing your rpm at those temperature points and taper that back to normal as it warms too.

For example. An sr20det likes around 150% MORE fuel when it starts, sometimes 200%, and i idle it at around 1500 rpm slowly tapering to 900 as the engine warms.

Its really just about giving it what it wants (=

13:1 'should' give you a pretty good idle quality even when cold. What is the ignition timing doing during cold start idle? What is the idle speed target when cold? As mentioned by 13bjunkie, you may get better results with a slightly increased idle speed. Of course the other possibility is that there is a mechanical or electrical issue that's affecting performance. How did it respond on the factory ECU?

Spark @ 10deg

Idle speed target @ 1200rpm

Still checking.


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