Idle roughness issue with 2005 Mazda 3i

[xBa380]

Hey guys,

I have a question regarding my girlfriends Mazda 3. Car has around 65,000 miles on it give or take. At idle, the car with "shudder" and the rpm's will raise/lower and you can feel it through the steering wheel and such. A new battery was just installed the other week and the alternator checked out perfectly fine. Air filter is new. Spark plugs replaced about 5k miles ago. No engine codes or anything out of the ordinary.

What could cause the engine to struggle like this at idle? I think it could be fuel filter or something, but don't have that much experience to know for sure. Could you guys lead me in the right direction what to look for, possibilities for this idle?

Appreciate the help, thanks!

 

[bdcardinal]

fuel filter is not serviceable on that application.

is it the 2.0 or 2.3L motor? had issues at work with the intake manifold shutter valve and throttle bod assemblies on the 2.3L

 

[xBa380]

2.0L motor.

 

[Eddie]

Intake air leak or vacume hose off or broken. Defective spark plug wires.

 

[ArcticCat]

This sounds very much like a faulty purge valve, a VERY common problem on the Mazda3's. I've had mine replaced once already because of shaking and 'bouncing RPM' at idle.

 

[bdcardinal]

Originally Posted By: Eddie
Intake air leak or vacume hose off or broken. Defective spark plug wires.


no spark plug wires on this application.

any codes present? the purge valve assembly that runs over the transaxle leaks a lot.

 

[mechtech2]

Clean your throttle body bore and plate dinner plate clean. Solvent and a rag works well.
This cures a lot of idle anomalies.
If you have to go from there, at least you did a good thing and have a solid base to start with.

 

[ViragoBry]

The last time I experienced this behavior in a car, I poured in 2 bottles of Chevron Techron Fuel Injector Cleaner, filled the tank and drove until it was on fumes. Vast improvement in throttle response and idle smoothness. 1994 Mitsubishi 3000 GT.

My mom's 1985 Honda Accord SEi started exibiting this behavior at around 50K miles and it also turned out to be dirty injectors. VERY low, rough idle while in "Drive" at stoplights. Fuel injector service cleared it right up. The Honda tech told my parents to stop using the cheapest gas they could find.

I had a 2004 Mazda 3i but didn't keep it long enough to experience what you're seeing. But it sounds like dirty injectors to me.

 

[artificialist]

Originally Posted By: mechtech2
Clean your throttle body bore and plate dinner plate clean. Solvent and a rag works well.
This cures a lot of idle anomalies.
If you have to go from there, at least you did a good thing and have a solid base to start with.

Also be sure that you get the cleaner into the IAC passage, otherwise the amount of air at idle will be too limited.

Some of the newer cars don't have this.

 

[bdcardinal]

Originally Posted By: artificialist
Also be sure that you get the cleaner into the IAC passage, otherwise the amount of air at idle will be too limited.

Some of the newer cars don't have this.

normally good advice, but does not apply to this vehicle. it is fly by wire so no IAC.