Chevrolet: Pre-starting lag, chevrolet impala, throttlebody

Question
Dear Grip:

I own a 2000 Chevrolet Impala with the base model 3.4 V6 motor. Whenever I go to start up the car, it lags and sounds as if the battery is dying out, although after 2-3 seconds the car revs faster then starts and runs normally. This happens every time i go to start the car up and is especially noticeable on a cold start rather than after the motor has been running for a while. Do you have any ideas what may be causing this lag? This has been happening recently and i have not noticed it before, as the car used to crank normally and start immediately without the lag effect. Any ideas or comments are appreciated. Thank You.

Answer
This used to happen to my 1997 Grand Prix GTP. The alternator was dying and killed the battery. Do you have a voltmeter? Can you check how many volts come out of your alternator and battery?

I'd also clean your IAC module in the throttlebody.

This is another common cause:


Too much air is getting through the throttle body (IAC stuck open).
O2 sensor registers lean mix (too much air).
ECU adds fuel to achieve correct mix.
RPMs increase due to increased fuel/air supply.
At 1500 RPM the ECU goes into decel mode and cuts fuel.
With only air coming into the engine, the RPMs drop rapidly.
At 1200 RPM the ECU turns the fuel back on.