Rough idling/sputter.....Im stumped
Thread Starter
Joined: Jul 2017
Posts: 25
From: Sacramento, CA
Rough idling/sputter.....Im stumped
6th Gen 2001 Monte Carlo 3.4L
Recently my car has began to idle rough and sputter. Not horribly bad but It has stalled out on me a few times. Once at a red light, once in the drive thru, and once while on the freeway offramp. It basically runs like crap when im not on the gas and the rpms go down. Feels like its out of gas. My first guess was bad spark plug/coil but No check engine light is on. Scanned for trouble code and no code. Scanner also measured rpms at 785-800 when idling. Theres no vacuum leaks. The weirdest part is if i turn the heater on a put the vents to defrost the car idles fine.
Recently my car has began to idle rough and sputter. Not horribly bad but It has stalled out on me a few times. Once at a red light, once in the drive thru, and once while on the freeway offramp. It basically runs like crap when im not on the gas and the rpms go down. Feels like its out of gas. My first guess was bad spark plug/coil but No check engine light is on. Scanned for trouble code and no code. Scanner also measured rpms at 785-800 when idling. Theres no vacuum leaks. The weirdest part is if i turn the heater on a put the vents to defrost the car idles fine.
MOTM Mod
Joined: May 2013
Posts: 5,499
From: Nebraska
There is always the fuel filter that might be plugged too.
Air filter could also be an issue.
Spark plug wires might be cracked.
I have something like this on a 2006 Pontiac Torrent with a 3400 motor.
I have put new plugs in it new wires.
It runs horrible at first and when it warms up it idles out of it. Still on the hunt with it.
Air filter could also be an issue.
Spark plug wires might be cracked.
I have something like this on a 2006 Pontiac Torrent with a 3400 motor.
I have put new plugs in it new wires.
It runs horrible at first and when it warms up it idles out of it. Still on the hunt with it.
Joined: Apr 2010
Posts: 12,605
From: Mentor, Ohio
My first question is, how many miles are on the current plugs and wires. If you have over 100K miles, I would replace them, as they are only rated to last 100K, 150K is pushing it.
You symptoms sound like it could very possibly be the plugs have reached end of life. Typically when all the plugs are worn close to equal and go past when they should have been changed, they don't mis-fire, but they also don't produce a good spark anymore, making it easy stumbles and stalling issues to occur.
You symptoms sound like it could very possibly be the plugs have reached end of life. Typically when all the plugs are worn close to equal and go past when they should have been changed, they don't mis-fire, but they also don't produce a good spark anymore, making it easy stumbles and stalling issues to occur.
Monte Of The Month -- January 2016
Joined: Feb 2013
Posts: 2,293
From: Pacific NW
How have you ruled out a vacuum leak?
You say the idle smooths out when the HVAC blower is on. The HVAC controls are vacuum activated on earlier 6th gens. A common problem is a break in the plastic vacuum line for HVAC that runs along the firewall, down the passenger side strut tower and down alongside and under the battery. I've had three gen. 6's that have had that line break where it passes hidden into a wire loom causing rough idle and slightly lower HVAC blower air pressure. If it's broken one end will be loose where it runs down the strut tower and you can pull up on the line and see the broken end.
You say the idle smooths out when the HVAC blower is on. The HVAC controls are vacuum activated on earlier 6th gens. A common problem is a break in the plastic vacuum line for HVAC that runs along the firewall, down the passenger side strut tower and down alongside and under the battery. I've had three gen. 6's that have had that line break where it passes hidden into a wire loom causing rough idle and slightly lower HVAC blower air pressure. If it's broken one end will be loose where it runs down the strut tower and you can pull up on the line and see the broken end.
