Hello,

Just found this forum and glad to be aboard and part of it.

I have a 2004 MC LS with the 3.4 with around 87k on it. It's been a great car so far but I've been having a problem with it recently.

When I start it in the mornings it will shake like it's running on 4 1/2-5 cylinders for a minute or so, then smooth out and run fine. So far I have removed the mass airflow sensor and cleaned it with MAF sensor cleaner, seemed to help briefly (maybe), but back at it again after a day or so.

Where to next, any surefire troubleshooting available? I am not too savvy on these newer cars and all the sensors and have no equipment other than a voltmeter.

Any help would be appreciated before I head to the stealer and get bent over.

Thanks

 

Welcome to the forum John!!

It starts rough and then after minute or two runs fine. Are you loosing any fluids? When it's running rough any unusual clouds of smoke from the exhaust?

If you are loosing coolant and you have clouds of white smoke, it's pointing to a head gaskets.

If not, my next thoughts would be to remove the throttle body, clean the carbon off it. Remove the IAC and clean the gunk off it. While it is off, remove the EGR. Clean the passage way between the EGR and the intake (the exit is behind the throttle body). Carb clean is good for all this (and some small scrub brushes and a piece of wire to push through the EGR passage).

At your mileage, you should also consider changing fuel and air filters. You're also coming close to time to change plugs. For good maintenance, I would recommend replacing the plugs and wires (do not use BOSCH plugs, stick with NGK or AC Delco).

Around your mileage, be prepared for the nylon lower intake gasket (LIM) to fail. If it does, replace with the Felpro aluminum ones. On the 3400, loosing oil or coolant from a LIM failure is common.

Hopefully these ideas lead you towards a fix.

 

Thanks for the reply, I'll start looking into all of this. Definitely will do a fuel filter today.

 

No issues with fluid losses coolant is fine and has stayed at present level for a long time. No clouds of blue, black or white smoke at idle or startup.

Didn't go to this extent, maybe should have. I have run Lucas Fuel treatment through it before and never seen an improvement. Also should probably start running top tier gasoline for the constant cleaning they provide.

I did clean the MAF Sensor with proper cleaner, replaced the air filter, fuel filter and plugs with the AC Delco 41-402. Still starts the same way first thing in the morning.

Certainly hope not, maybe time to sell it and get a new one.

Car is at the stealer for some troubleshooting, hope they can come up with something. I'll post when I hear something.

 

I never see fuel treatment resolve a rough idle and don't throw money in higher octane fuel. Those two items more then likely are just tossing money away (if you want to throw money away, feel free to PayPal it my way lol).

I would really suggest cleaning the IAC and EGR passages (even if they don't need it, they only take a little time to do and are good maintenance).

You may also want to consider checking for vacuum leaks.

I assume it's not actively throwing a CEL?

And if you think the dealer repair shop is a "stealer", I wouldn't take my car there. I've seen some many people make those references, I just find it funny. If you feel they are going to rip you off, if you have no warranty reason to take it to them, find a trusty mechanic.

Let us know what their results show.

 

We had a somewhat similar issue with our '04 LS where, on a cold start, if I had to drive up a steep ramp at my parking lot, the car would 'stumble' while climbing the ramp, as if the transmission was 'hiccuping'.... took out the EGR valve, cleaned it out some (even though it didn't appear to have any carbon), and no more issues with the stumbling on the ramp. Car runs real smooth now.

 

I'm thinking dirty/sticking injectors or a defective fuel pressure regulator that's allowing pressure to bleed off when the car is sitting.

 

The dealer did not find anything wrong with the car except a battery that was about to go so I replaced that. No help.

I ended up trading the car on a 2013 Buick LaCrosse last weekend. Got $4,500 trade-in which I thought was really fair so I did it. Didn't think I would get a lot more selling it outright. Biggest reason for selling was I am headed into retirement in a couple years and didn't want car payments so if I got a new car now, I would only have about a year of payments after I retire.

The Monte was a great car, I owned it for 9 years and had only a few problems that the dealer took care of very satisfactorily for me. If Chevy were still making the Monte I would have probably bought another. The Lacrosse is a very nice vehicle and I certainly hope I get the service out of it that I did the Monte.

Thanks for the warm welcome and all the attempts to help, I appreciate that.