Hi folks, my wife and I have a 2003 Monte Carlo SS. It has the 3.8l normally aspirated engine and has just over 70k miles on it. We bought it in 2004 with just under 20k miles on it and it's been a good car for us. It does have one little annoying problem with it that we can't seem to eliminate, or even find what's causing it and I thought you'd guys might have an idea. We've taken it to the dealership, Dale Earnhardt chevrolet in Newton, N.C., several times and they tell us that it's a fairly common problem with GM products from this general time frame, but I find it rather annoying and it somewhat scares my wife.

Basically it's this, when sitting still for an extended period of time, stop light, stop sign, heavy traffic, etc. the car begins to stumble and even shuts off on occasion. The RPM's will drop, the undervolt low light comes on etc., etc. Doesn't matter what, or how many accessories we've had turned on or off, it's done it with the radio off, no A/C, fan off, windows already down, doesn't matter. Now, if we put the car in neutral and keep the RPMs up while stopped, it works just fine, but I find it annoying that I have to do this with it. It doesn't do it right away, only if we're stopped for a good bit of time, a couple of minutes for instance, but it's still annoying. Anyway, the dealership has checked the alternator and wiring, it had a new battery put in it a few months ago, and there has been no change. Is it true that this is a common problem with GM cars from this time period, or is there something I can do to fix this problem?

Thanks for any ideas you folks may have.

Chris

 

Welcome to MCF Chris!!!

I've never heard of this problem but it could be a few things. One I would get the cat converter checked on it. That sluggish stumbling prob sounds to match.

It could also be injector, PCM, throttle, and a few other problems. I would recommend trying some ethenol based gas like E-20 to help clean up the internals.

Also try Shell gas - it is a reformulated product that keeps the valves clean. I can verify this with a neighbor I helped install rockers in. My car gets Shell and BP and mine were clean. He used Kwik Trip and they were disgusting. He switched to Shell and BP and we checked 2 months later and they were pretty clean.


You could also try the volt booster kit from ZZPerformance.com. Look under electronics, but I think that is a band aid and not a solution for the problem at hand.

 

Duh... also check your air cleaner and spark plugs.

There is also a product called SeaFoam that I've heard people use to clean the engine internals as well.

 

I'll certainly check on those things, I've heard of the SeaFoam stuff, but never tried it so I'll look around for it. The thing that bothers me about all this is that it's been doing it since the day we bought it. If it was something recent, I would certainly think about the things you were mentioning, but it's been doing it since day one. When we first bought it, it had a problem going into overdrive, which turned out to be a switch in the transmission. The dealership replaced that for us after we had the car a few weeks and I remember bringing it up to them and that point. They've looked at it a couple of times and always stated it was something that was an issue with GM cars around this time period. I just find that hard to believe and was wondering if anyone else has seen that.

 

To me it's pure and simple. If it runs rough at an idle, like at a stop light, without throwing codes, like a mis-fire will do, the it's dirty injectors, and they were probably dirty when you bought the car, and are worse now. Let me make another guess, you buy the absolute cheapest gas available? When you start having problems like this, how cheap is the gas now. I NEVER have a rough idle, and I only put Seafoam in my tank MAYBE once a year. Quit buying cheap gas! Buy ONLY top tier gas, and it's not usually any more expensive, but stay away from the independents and the department store chains that buy THE cheapest gas available.
So what to do now? Start with one can of Seafoam injector cleaner in the tank, and "drive it like you stole it". If you don't, you just loosen it up and could actually make it worse if a chunk of gunk moves without going out the injector nozzle. Sounds like you could use a couple of tanks of this, and probably could use 1/3 of a can in your vacumn line running into the throttle body to clean it out, also. Forget anyother brand of cleaner, as it's just a waste of money.
So what brand of gas to buy? Shell, Amoco, Chevron, or one of several other "top tier" brands. There is a thread on top tier gas, I believe, or search Google.
Also, you're plugs should be fine for 100,000 miles or MORE! You can pull one and check, but don't buy new ones UNTIL you check, as they're expensive. Put NGK Iridium's in when you do. Ignition wise, I've found coil-packs to be more of a problem than wires or plugs. Ignitions problems WILL throw a code.

 

I'm betting on the Air Filter.
The Air Filter is too easy to forget to do scheduled maintenance on. For the price of a new filter element and 45 minutes work ... you can slap a new air filter in there and make sure you ain't getting choked-out at low vacuum.

My air filter was caked with crap. Road, mud and dust that wouldn't vacuum off or dislodge when I slapped it on the bench. I put a new air filter in that baby and after five driving cycles the car ran like a brand new car.

 

I'm not going to disagree with y'all, but it looks to me like if it was dirty injectors or air filter, it would be REALLY REALLY bad after 50,000 added miles. But i'd check those areas anyway, won't hurt.
Mine has 112,000 on it. It stumbled once a while back, then a couple days later threw an EGR code. But I guess whatever was wrongrighted itself because the CEL turned off and it runs fine. Was running fine at the time of the stumble too, except for the onestumble, LOL. I had decided it was my imagination since it only did it once.
Have you put a scanner on it to see if there are any codes there? (The dealership probably has but thought I'd ask anyway).

 

Well, we'e kept up with the maintenance, I don't think the air filter is much more than 6 months old at this point, I changed it before we went on vacation in Sept.. The gas is a posibility, my wife does most of the driving and while she always puts 89 octane in there, I can't vouch for the gas stations she's been visiting. The dealership did mention checking for codes a couple of times and say they found none. The CEL has never been on besides the problem with the switch in the tranny when we first got it. I'll get some Seafoam and give that a try. Thanks for the ideas so far.

 

Personally ... In my own opinion ... just me; I guess ... but, ... spending 40-Bucks for Iridium Spark Plugs and leaving them in for 100,000 miles is nuts.

I'm spending less, for Platinum and replacing them for Brandy Newsies every 9,000 miles.

I don't buy into the hype on Iridium Plugs. They're Spark Plugs. Expendable.

You run them for awhile and then get rid of them for new ones!

Simple as that.