I have a 2005 G35 coupe that I don't drive often. I was messing around with the throttle body a few weeks back and forgot to plug back in the main harness to the throttle body

Yesterday I needed to start the car and it started right up - I hit the gas and it slowly revved a few hundred RPMs, like it was in limp mode. I shut the car off and restarted it and again it felt like it was in limp mode. I then remembered that I had unplugged the throttle body. I popped the hood and sure enough the throttle body wasn't plugged in.

So, my question, is how were the RPMs raising when I pushed the pedal if absolutely no wires were connected to the throttle body?

I plugged the harness back in and restarted the car and everything was back to normal, but I'm still confused how the motor was spinning faster with no throttle control.

 

My bet would be added fuel , i've accidently done the same thing.

 

So I should be able to see the motor run rich under that circumstance - I'll have to check that out later.

The other thing that has me puzzled is how does it even idle with the TB completely closed? The TB is spring loaded and I believe sealed up somewhat tight in the closed position - the car started and idled fine. I have a spare TB sitting around I need to look to see how much airflow it allows when it is against the spring.

 

I've been thinking about it some more, and I am betting that the motor is advancing timing, causing it to pump more air in through the slightly open throttle body, causing more fuel to be added.

I can check all this with a data logger to see if:

1. timing changes
2. MAF voltage increases, even though TPS stays the same
3. O2 voltage stays near the same spot (will be hard to tell though in open loop).

 

During warm up the ECU is in open loop and plenty of fuel pouring in??