If I start my engine when its warm, it will run really lean almost ot the point it will die out. Maybe around 14-15:1 a/f ratio. Its a street ported engine with stock s4 turbo setup. After about 30 seconds of running lean, it goes richer, to the normal idle. Why would it go lean in the begining?

 

IAT sensor heat soak is one possibility. Do you have a log of this behavior? That would help a lot.

 

Thanks, I will be borrowing a friends labtop to tune my car, this will happen in the next week. Thanks. I will check it out

 

iat heatsoak is probably it. my friends squirted car has the same symtoms. try unplugging iat after you start it and it should run fine. from what i hear the MS need to delay the iat control over fuel correction.

 

I had that trouble with an S4 n/a setup. Moving the air temp sensor from the manifold to the intake ducting helped greatly.

My turbo install uses the n/a throttle body elbow. I've tapped the elbow and threaded the sensor right into the elbow itself. Heat soak has been minimal with this arrangement.

 

I was curious what the ecu does if the sensor gets heat soaked? SO the temp its getting is hotter, so the engine runs leaner?

 

Higher intake air temps result in reduced air density. Reduced air density requires a leaner mixture for the same afr.

After shutdown with a hot engine, the entire engine compartment including the air temp sensor will increase in temperature. On startup, the hot air is quickly swallowed by the engine, with actual intake air temps falling quickly to close to ambient. The sensor itself may see some delay in response depending on it's mass, mounting location, and exposure to the intake airstream.

 

thanks

 

so what can we doto compensate it for it?

 

There is an IAT heatsoak correction, you may want to try using that.

Otherwise, just move the IAT sensor out into the plastic part of the intake away from the engine... it'll cool off faster there after heat-soak.

Ken