Hello, Im new to this forum. I have a 2005 ls with close 89k on it and i'm getting a random misfire code. It only misfires when its warm and idling. Also when its warm its hard to start, I usually have to give it some gas. When its cold, its starts right up and idles perfect. I'm pretty good at working on cars but not too great at diagnosis So far Ive changed spark plugs and wires, cleaned the MAF and replaced a bad vacuum line. I'm a little tight on money so I want to try to fix it for as little as i can without putting on cheap parts. Thanks in advance for your help

 

Welcome to the forum.
Sorry to hear your having trouble...
Pls post some pics of your Monte Carlo.
Feel free to join in on the conversation in the daily blog!

Cleaning the MAF... doesn't always help....

But the first thing i'd check is your fuel pressure at the fuel rail....
Have you changed the fuel filter? recently?
Most auto parts carry a tester you can use to check it with.

Maybe someone else will chime in with some more ideas.
Thanks for joining the MCF Family.

 

I had the EXACT same problem. Mine was caused by an Aftermarket MAS then by a bad MAS. But I would follow Stumpmi's advice have the fuel system checked, Also your MAP and PVC, FPR and EGR. DEFINITELY clean your mas.
The fact that the problem exist aft aft were the engine has warmed up points me to an electronic part that over time can start to be effected by heat.
Just Keep in mind that even though they are all Montes, each car is still different and can show the same Simpson for different problems. So do your checks first and go from there!

 

Thanks for the welcome! And I definitely will post some pics.

I discovered the vacuum line I replaced slipped off so I put a clamp on it and now it starts a little easier again but i'm still having to give it gas. I'm planning on doing the fuel filter tomorrow. I'll you know how it goes afterwards. Thanks for the advice. If this doesn't work I'll get the pressure checked.

 

You may wanna also clean the TPS (Throttle Position Sensor)
May help your throttle response....

Heres a diagram that may help...

 

should i use a throttle body cleaner or something lighter like MAF cleaner?

 

Okay, the filter is changed and the TPS is cleaned. It seemed better on the test drive but i'll have to let you know for sure.

 

I knew I wouldn't get off that easy. Still doing it.

 

With you engine running, dis connect your Mass Air Flow Sensor. Your check engine light will come on, if it's not already, and the car will run in Closed loop mode. This is not the best way to run your car but if the MAS is the problem. The car will start when it is warm. If it does try cleaning the MAS with MAS cleaner. If it doesn't work after you clean and re-install it, then replace the MAS with a genuine GMAIL/Chevy part. I can tell you from experience that a cheaper aftermarket one could do the exact same thing.
Also know that your PCV valve/MAP sensor combination could cause similar symptoms.

 

I tried unplugging it before, and that didn't help. And how do you remove the pcv valve? It has a riveted bracket on it