Engine turns over well, but will not start. Sometimes waiting until it cools down works. Other times disconnecting battery for 30 seconds seems to reset something and it will start up.

Is your Impala a 2000, 2001, or 2002? This seems to be a common problem in those model years...much like its predecessor the GM VATS (Vehicle Anti-Theft System). While the VATS had a permanent (albeit unapproved) solution, no suck workaround appears to be available for the Passlock system. Some websites offer a correction "module" that looks to be a hit-or-miss solution. I did find the following procedure on a forum, and it seems to be reliable. Here goes:
If your car has been sitting while you were at work or home or in the store, and you are coming out to leave, follow steps 1-6.

If you just had the SECURITY SYSTEM lock you out of the ignition system, you will have to wait the 10 minutes for it to reset and allow the ignition control module to interact with the system. Once the 10 minutes have passed from the ACTIVE SECURITY STATUS, follow steps 1-6. Do not try to shortcut this as it wont work.

If it is raining, you can close your door, just not all the way. Close it all the way and open the door latch without pushing the door open. This will keep you dry.

+++++STEPS+++++ 1.) OPEN YOUR DRIVERS DOOR AND SIT DOWN. 2.) PLACE KEY IN IGNITION, WAIT FOR CHIME. (3 seconds is what I usually wait) 3.) TURN IGNITION 1 CLICK RIGHT (TO THE ACC POSITION) AND STOP! Do not continue to ON and START yet. WAIT ATLEAST 5 SECONDS 4.) AFTER 5 seconds has passed, TURN KEY TO ON and STOP, DO NOT CONTINUE TO START YET! 5.) WAIT AND WATCH. With your drivers door open, here is what you will see and hear = Your notification will signal DOOR ADJAR, then the BATTERY light, then the SECURITY light, during which you will hear the chime sound as if you just started the car. 6.) AFTER YOU SEE THE SECURITY light switch back to DOOR ADJAR or Battery, and after the CHIME has stopped, you can turn the key to start and voila!

It has worked every time for me and 5 of my friends. This whole process takes about 20-30 seconds, but it sure as hell beats 30 minutes, as GM refuses to compensate my time lost to their vehicle\'s design flaws.

RECAP: 1.) Open driver door, sit down 2.) Insert key in ignition, wait for chime 3.) Once chime starts wait 3 seconds 4.) Turn key to ACC position WAIT atleast 5 seconds 5.) After 5 seconds turn key to the ON postion and wait for the security light to switch back to Battery or DOOR adjar, and the chime to stop (Do not try to START if the chime is still sounding) 6.) Once chime stops and Security light has passed, You may now complete the turn to START and it will start.

Note: This is not a permanent workaround, but it will buy you some time, I can almost guarantee it will work for most if not all people, almost all the time.

It actually supposed to work like this. It should turn off in a couple of minutes. Give it a try. Wait for like 10 min to see if it will stop.

Many cars have this feature. The fan will run for a few minutes at a time until the coolant in the radiator drops below a certain temperature. Most vehicles with this feature will have a warning label on the radiator shroud indicating that the fan may start without warning when the engine or radiator is still hot. The only time you would need to be concerned would be if the fan continues to run without turning itself off, and causing the battery to be drained.

Had same problem last year in my 04 Taurus with V6 12 valave Vulcan engine. Engine spins over OK, fuel is pumping (you can smell it at tail pipe) but intermientently would not start. Sometimes would start on the first try, sometimes and the 10th, etc RIght after trying to start all gauges would peg all the way to the right for 20 or 30 seconds. Took it to garage and they said I would have to wait until it totally failed, their diagnostics could not troubleshoot. Finally it totally died. Engine never turned over sluggish, always spun over nicely until it just died completely. Then I could not even get a click out of the starter. I called AAA, they showed up and immediately the guy said, bad battery. He had seen the same symptom in quite a few Taurus's. I told him that it suddenly stopped and never had symptoms of a weak battery. He replaced battery and all has been perfect since ... go figure? Almost sounds like something may have been intermienttly arching internally to the battery, creating non-DC "dirty electrical noise" and freaking out the computer. Who knows .... ?

Take it to a different shop. Something is wrong with it. However, when the airbag light is on, that means the airbag will not deploy in an accident. You should have that fixed first. The dealership is the best option for making the keyless entry work. If this was at all helpful, please rate. Thanks for asking.

next time it does it try turning the key on without starting it. wait for the light to go off then try to start it.

It appears to be stuck-open throttle maybe due to a bad throttle cable or a broken return spring. Check the operation of the throttle with the engine off, and don't start the engine until this problem is repaired. Hope this helps!

I have the same problem. Short term answer for me is to disconnect battery for 30 seconds and then the car will start. I have the infamous dashpod problem and the keys and eveything are coded into the dashpod so I'm hoping when I get mne replaced the immobilser problem will go to,at least the guys who work on my car reckon so.
With the regular need to disconnect he battery I leave the three screws for the battery cover finger tight and the battery contact loose enough to wriggle off. I can do it start to finish in a couple of minutes but is a mjor pain still.

I would definitely consider the fuel pump. I had long turnover times before starting for years, but even worse was in hot weather it would just stall while driving. Sometimes it would only idle, but not run if you pressed the gas very far. Park it for 20-30 minutes and it would run again without another problem for weeks. Dealers and mechanics kept replacing other things like ignition coils and distributors. After a conversation where someone said they had the same problem, but only when they had less than half a tank of fuel, I knew it was the pump. I replaced it myself and all problems went away.
The fuel leaks back down to the tank and air gets in the lines. Then the pump is slow to build pressure up again. If you turn the key on, but not start, wait 45 seconds, off, on again but not start, wait again, now start it will take a little less time to start, less battery drain, until you fix the problem.
You may not have the heat problem in Canada. But here in Georgia it gets hot enough that if the fuel tank is low and the pump has this problem, it will overheat and shut down till it cools. A full tank helps it keep the pressure up and serves to cool the pump.

Replace the cooling fan engine temp sensor switch, this may be the cause.