Our '05 Monte carlo is running rough after it first starts up. It clunks and bucks and makes all sorts of unwanted noises. as soon as you give it gas it runs fine and it runs fine at speed. Already did a tune up and replaced the fuel filter. Any thing else i could look at? could the oxygen sensor cause this? Thanks in advance

Did it do this before your tune-up? Is there a check engine light on?

yes it did it before the tune up.. the check engine light is on and the code says the o2 sensor. its actually getting worse..tonight it sounded as if the starter was starving for power to kick it over and it was hesitating to start.

Clean the throttle body. I'd bet the idle circuit motor is stuck with grime.
Never mind. That wouldn't throw a code. Always more details helps.

Jeff, how do i do that?

Edited my earlier post sinc you added details, but you can get crc throttle body cleaner at flaps. Spray the inside of the throttle body without the car running. There is a small hole just before the butterfly valve. Get that good with the cleaner. Cycle the key a couple times, the pintle on the idle circuit motor will move in and out. Spray till no black crap comes out. Start car. It will start and run like crap till the cleaner burns out. Btw your symptoms sure sound like the typical intake manifold leak on the v6 motors. Getting coolant in the oil?

Thanks Jeff..I will try this ...as for the coolant, i will check it..these cars suck too

What is the code? P0420? Coolant leaking from your intake into the catalytic converter will kill the cat, causing O2 sensor and Catalyst inefficiency codes to come up. Cats and O2 sensors are a symptom of a deeper problem...

not sure what code # ..the place that did the tune up just said it was for the "front O2 sensor" I did not have them replace it because they wanted too much money to do it and I figured i would replace it myself.

Most codes do not have a description saying "sensor #1234A has failed". You would most likely get an "O2 sensor bank1 sensor 1 circuit fault" description, and have to watch how the sensors are acting in relationship to eachother to diagnose what is going on. Plugged cats often come up as an O2 sensor code. Take your car to Autozone/O'Reilly or whatever is close to you and get the code checked for free. Better yet is shopping online for an OBDII code reader online- you can find one for $20 and then you can check codes yourself on any car you own that is newer than 1995. Google the code you find and you will get a lot of information to point you in the right direction.

I get people in the shop all the time who have "done it themselves because 'my mechanic' or 'the guy at jiffy lube' wanted too much for the job". They've bought a cheap POS part and put it in, often incorrectly, and the problem hasn't gone away. Lotsa times it's because that wasn't the problem to begin with, sometimes because they used cr*p parts or screwed up the installation. Or they broke something else while they were in there. A vacuum leak can cause a rough idle and an O2 sensor code, so can a dirty TB or a leaking injector. Do yourself a favor, take the car to someone who is good at driveability and knows Chevys.

BTW, the smog guy next door has a fairly cheap generic code reader that is easy to use and good for quick basic "get you in the ballpark" diagnosis, and it "can" be useful in the hands of an expert, but the guy at the FLAPS isn't one of those. He sells parts, the more the better. I get people in all the time who own a cheapie scanner, and they are all too quick to tell me what's wrong with their car. They're rarely correct. There are hundreds, if not thousands, of codes and manufacturer specific sub-codes, and it takes years of training and practice to be able to interpret them. Cheapie "code readers" won't give you anything but the most generic federally mandated information.

The Cap'n

Oh, and BTW, if it is the intake manifold leak, DON'T BUY AFTERMARKET GASKETS!. Cheby went through at least 4 design changes on those. The latest ones hold up pretty good. I think the intake gasket set is ~300 from chevy. Labor and parts will be over 2000 bucks! If you were closer, my old neighbor does them at home all the time, in fact he has bought several GM cars that were near perfect except the intake leaks for next to nothing.

Thanks for all the helpful info guys...I will let you know what happens

checked the oil and there is no coolant visible. went to the local flaps and did another scan came up with P0135 O2 sensor heater bank 1 sensor 1.....and code P0455 Evap. emissions system leak gross leak/no flow. Anyone? P/S I did order a O2 sensor should have that in a few days and i am going to replace the fuel cap(cheap insurance)..also going to check for a possible vacuum leak

Check the fuses in the engine compartment. The first code is a heater failed on one of the primary o2s. Second one could be a evap solenoid or gas cap even. With both codes, I'm wondering if you just blew a fuse. I'm not sure what side is bank one, on the rwd cars it would be drivers side I believe.