2003 impala wont run right

When I stop at a stop sign/light then try to go again, my car loses power but it does not die. When I push the gas pedal, it will only go about 20 mph. Eventually, it will go at normal speed but it takes about two minutes. Going uphills is a nightmare!! The check engine light does not come on. I have had a complete tune up done but it still does not run any better.

I took it to a mechinic to be tested and he had said that when I had the battery replaced it wiped out the codes on the computer. He said that I need to take the car to a chevy dealer to have them reset the computer because he can not do that. Does this sound right? Is it possible to reset the computer myself? The chevy dealer can not look at the car for 2 weeks, and this is my only car. I need to drive it now!

2003 Chevy Impala V6 3.8 liters

How many miles do you have? Did you check(fuel filter, CAT,etc.)Do you feel tranny slipage? About PCM i really dont think, that you did something. I am disconnecting battery every week to do some works.

I have 85,000 miles on the Impala. The fuel filter was replaced 2 weeks ago when the tune up was done and the tranny does not slip. I didn't think that unhooking the battery would wipe out the computer, but with these newer cars and by taking the mechinics word, I thought maybe it could happen. my brother had mentioned tht it might be the fuel pump going bad. Could that be it, or would that have shown up when the car was analyized?

This sounds like a clogged Catalytic Converter... It's a very common problem and GM has extended the warranty on the CAT because of this... I experienced the same as you are describing and finally the dealer verified the clogged CAT condition and replaced it... The car runs like a rocket now... Go to your dealer, tell him this and make sure he checks the CAT when the engine/exhaust is fully warmed up... BTW, my car didn't throw any codes either with the clogged CAT...

don't go factory CAT. They will clog agian. I had a flowmaster hi output CAT put on and it runs faster than a stock imp. even sounds better at the exhaust. The only down fall is if you don't use a device to tell the O2 sensor that everything is fine the check engine light will come on and stay on. I've gotton used to it by now. The part is only about $30 just haven't taken the time to do it. GM paid for the whole repair and it was only $169. I've even heard people that had the stock CAT put back on and the car still threw the same code. CAT is running below proper thresh hold levels or something like that.

I took car to a muffler shop in my town, he checked it over and said that the CAT was not clogged. Any other suggestions?

I took car to a muffler shop in my town, he checked it over and said that the CAT was not clogged. Any other suggestions?

How did he check the CAT?

He had said that if the CAT was clogged it would overheat. It has never ran hot. He also put his hand over the exhust while the car was running and said their was lots of pressure coming out and if the CAT was bad there would not be much pressure.

As you can see I do not know much about cars, just that I am fustrated with this one!

How car start? With no problem? Bro we need more symptoms, then maybe we can help you. I have ALLDATA maybe i can help you.

The car usually starts without a problem, but sometimes I need to push on the gas a little. The only syptoms the car has is losing power. Once I get it going, it will run fine, until I need to stop again. It acts like it is misfiring but it is not throwing any codes to the computer anyalizer and the check engine light has not came on. The car has been running like this for about 2 weeks.

the car will not over heat, it didn't in my case. putting your hand over the exhuast is not a correct way to check. The baffling in the CAT breaks away and clogs it up. This is a common prob. Take it to the dealer and pay 50-70 to have it checked. Most won't charge if they can't find anything. It could be your BCM. Have them reprogram it

He had said that if the CAT was clogged it would overheat. It has never ran hot. He also put his hand over the exhust while the car was running and said their was lots of pressure coming out and if the CAT was bad there would not be much pressure.

As you can see I do not know much about cars, just that I am fustrated with this one!

Your mechanic is totally wrong and sounds clueless!!... The car will not overheat with a clogged CAT... And putting your hand over the exhaust output is not a correct way to check backpressure... I suggest you follow the suggestions in my previous posting to you... Unless something else is going on that you are not describing correctly, a clogged CAT is the most likely problem... It's VERY common on these cars which is why GM extended the CAT warranty to 100K miles and replaces them at no cost to you...

Thanks for the advice. I will take it to someone else to have the CAT looked at again. I will let you know what I found out.

My 01 did the exact same thing yours is doing and it was the cat.

Here is the letter I got from GM about a year ago on the Catalytic Converter... As you can see the GM warranty was extended to 10 years or 120K miles... This also applies to 2002 and 2003 Impala's as far as I know...

http://i70.photobucket.com/albums/i85/gemstonian/Cat_Letter.jpg

Thank's for showing me the letter. I am going to call the chevy dealer first thing in the morning and try to get an appointment sooner than the one I have scheduled. (2 weeks from now) Hopefully, they can look at the car within the next couple of days. I am just surprised that the muffler shop I took it to said it was not the CAT and must not have checked it correctly!

If it runs ok right after you start it, then gets progressively worse as it warms up, it's the converter.

I was able to get the car into the chevy dealer today and they agreed with all of you that it was the CAT. Since it is still under warranty, there is no charge. I left it with them and they said I can pick it back up tomorrow!!

Thanks everyone for the advice! Hopefully when I pick it up tomorrow, I can drive away with no problems and back at the speed the car used to go!

Excellent!!! Glad we could help!! Now be careful and don't get any speeding tickets with your new car!!

you can buy a back pressure tester for under $70, you take out the ox sensor and sccrew it inplace.

How's your car run now, brandyh? Did the new cat. fix it?

I am having the same problem, with new cat. I think this is not the problem. Let see what happen with yours. Did you took it from dealer? What is going on?

sound sliek the cat man..my monte never overheated, it just had alot less power, still could hit 110 mph but took forever, and it got worse the warmer the car was, had more power when cold

The new CAT that the chevy dealer put on, fixed the problem. I got the car back tues around 10 am and have been driving it like crazy just to make sure it wasn't a temporary fix. The Impala runs as good as the day I bought it!
Gems--No speeding tickets yet!

Strange. I having the same problem and after cat was changed it never fixt. I am having direct fit(aftermarket). What is the different exept P0420.

The new CAT that the chevy dealer put on, fixed the problem. I got the car back tues around 10 am and have been driving it like crazy just to make sure it wasn't a temporary fix. The Impala runs as good as the day I bought it!
Gems--No speeding tickets yet!

Great!! Enjoy the new car feeling... Glad I could help point you in the right direction...

Strange. I having the same problem and after cat was changed it never fixt. I am having direct fit(aftermarket). What is the different exept P0420.


I do not know much about this topic, that is why I asked the great minds on this forum. All I can tell you is what I did. The chevy dealer said that the CAT is under warranty up to 10 yrs or 110,000 miles. Maybe, a factory CAT will fix your problem, if it is under warranty it is worth a try!

I do not know much about this topic, that is why I asked the great minds on this forum. All I can tell you is what I did. The chevy dealer said that the CAT is under warranty up to 10 yrs or 110,000 miles. Maybe, a factory CAT will fix your problem, if it is under warranty it is worth a try!

If he already installed an aftermarket CAT Chevy will not replace it with a factory CAT for free... If he had kept the OEM CAT on the car Chevy would honor the 10 year, 120,000 mile warranty on the original CAT and install a new one for free... As long as they first verified that the OEM CAT was clogged...

i didnt read what everyone else said, but on my chevy truck, this problem happened, and it was the fuel pump. oddly enough, my family's 01 impala has this problem too

Is it normal for the instrument panels lights to kinda be on when you start the car but then after a bit you hear a cllick and they are nice and bright? Only once have I started the car with no lights but after hearing the click they were on. This is a 2004 Impala.

Is it normal for the instrument panels lights to kinda be on when you start the car but then after a bit you hear a cllick and they are nice and bright? Only once have I started the car with no lights but after hearing the click they were on. This is a 2004 Impala.

Yes it is normal, I dont have the time to go into why that is happening, but it is normal, don't worry about it.

I had the same problem and it was the cat too, replaced with aftermarket and ran great afterwards.Mine lossed power and then started to buck sometimes upon acceleration before replacement.:2cents:
ronvb