Weird Idle

[mahyarv14]

So this morning, I started my car like I always do and was driving. After about 3 minutes of the car being on, I was at a red light. Noticed the chassis was vibrating randomly a tiny bit. Like it was shaking. Looked and my RPMs and saw it sitting about 600/700 but it was going up and down rapidly about 100-200 around. I could feel the engine act weird. It was 77 degrees out at the time. My AC was on and running but not high or anything. After I started accelerating, it went away and I didn't notice it happen anymore. My car is 100% stock with 13k miles on it. Auto PP built in 2015.

Any ideas what that was? Misfire?

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[connellcr3]

Check plugs.

 

[5.0yote]

You will get an odd idle when it is hot and running the AC when the radiator fan(s) kick on, that along with the AC compressor, this is not surprising.

It is a pretty fair amount of electrical draw on the system so your idle getting a little erratic or feeling erratic is normal in this situation. Next time it happens, shut off the AC see if it goes away immediately. You will have your answer.

 

[Regs]

Funny, I have been noticing this too and it is with the A/C on. I also had the issue with my previous Mazda 6 (built by ford) and it actually stalled on the road a few times from it.

 

[ForYourOwnGood]

Every 4 cylinder I have ever driven has had a hard time with A/C and fans on warm days at idle. Its a lot of load on an engine that typically doesn't produce much power down low, many tuners add 100-200 rpm to A/C idle for other platforms to help that, not sure if thats the case for these cars but I know they did for my MS3 for example and it helped quite a bit.

 

[TurboMetal]

This happened to me as well at a red light after I turned the AC on just before hitting the on ramp for the highway. Only happened that one time thou.

 

[Buhbuhj]

Mine did this before I got my tune. Engine seemed to not like idling around 700rpm or so. Adam turns up idle with tune and it's much smoother now.

 

[zoomzoom_30]

Mine does this too, seems only with the a/c. It also seems to be getting worse, or I just noticed it more lately. No discernable tick in tach, no lights etc. Has anyone taken it in? I'm afraid i'll get a "could not replicate" if I do

 

[Tash Oh]

my 5.0 does this too, pretty much on every single cold start I will have some idle play. It goes on every time I stop the car until the engine is fully warmed up.

 

[TheLion]

With the windows already up, pull both windows switches up for a second. You'll feel the alternator load the engine, I can feel it through he clutch pedal if my foot is just resting on it. Anytime there's a sudden load you'll get a bump in idle RPM and you can see a big jump in timing. Never owned a 4-cylinder that wasn't sensitive as the above posts mentioned. Compound that with AC and that's most likely what your experiencing. Also don't forget the 30lb flywheel, any sudden changes in RPM are going to be felt quite a bit due to all that mass.

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