07 Chev. Impala - strange problem

[ThunderLund78]

Hi everyone,

My impala starts fine, but as soon as it starts an goes to idle, my dash lights, radio display, headlights (if dark enough to be on pulsate from dim to bright over and over for about 10-15 seconds. After that period, it usually stops and the car is normal, but sometimes (maybe 1 out of 100 starts)the engine starts to run like it's out-of-time or missing on a cylinder. Almost like it's running out of gas and sputtering. The dash read-out gives me a warning "ENGINE RUNNING AT REDUCED POWER." I then shut it off, and try to start again. Usually it runs fine after the restart but sometimes it happens again. I should also point out that it only seems to happen on cold starts. If the car's been running a while, it starts and idles fine.

I took it to the "experts" at the dealership and all they could do is plug into the computer and tell me there's absolutely nothing wrong with it. They did go through the entire electrical harness/system and said it all checked out. They said they'd have to see it happen to diagnose it which would be almost impossible. I guess I could leave my car there overnight and they could see the pulsing when they start it cold, but the engine thing only happens occasionally--and I'm not even sure the two are related.

I don't have volt meter at home and they did check the battery--but only after the car had been recently running. Could it be that it's just not holding a charge that long and it has a tough time getting all the systems online on a cold start? Could the rough running have to do with the alternator supplying the current for the spark through the dead battery? Obviously I'm not an expert

Any advice, opinions, or suggested next steps on a fix would be MUCH appreciated!

thanks!

[Scott K]

I would have your battery tested first, then have your charging system tested. To me it sounds like a weak battery, or a bad ground to the engine.

You may have 2 different problems, but I would address the battery and charging system first.

[Dave S]

My mother in law has an '08 Impala that had the same problem. I don't recall the exact fix but it had something to do with the foot pedal and maybe a sensor.

She was getting the reduced power message that you are also.

[crothmeier]

Electronic throttle position sensor either in the throttle body or in the gas pedal. Ive replaced both on my '07 Imapala. Both spit out the reduced engine power message.

[Macgyver55]

You may have 2 different problems, but I would address the battery and charging system first.

I agree. I would hook up a volt meter before starting it cold and see if the voltage is fluctuating. A weak battery can cause this and sometimes result in reduced power mode because of the varying voltage at various sensors.

Do or did you have a check engine light at any time so that a code can be retrieved?

[gofishingtom]

i would say its the gas pedal that is what happened to out 07 impala and brother in law checy mech found the problem and changed out the pedal and car has been fine ever since