Stumbling idle when stopping.

[firebird1999us]

I had a similar issue but it turned out the alternator that I had recently replaced was not tightened down enough. I had cranked down the bottom bolt pretty tight but it was still not as tight as it needed to be. My mechanic got it on there tight and the car stopped a good bit of what I felt was mechanical vibration. I felt like I was in danger of overtigtening but I guess it had a bit to go.

My car has 350k+ on it... we also discovered through the whole process that the vibration I thought was an idle issue was actually the motor/transmission mounts failing. I was only getting a vibration when the car was in gear and I had the AC on at a stoplight when the car was under load. Now that we've pinpointed the mounts failing I can feel that the vibration is coming from the direction of the transmission and lower motor mounts.

There's also an Idle Control Valve that can be problematic too... I believe it's located under the throttle body? Those are fairly delicate and expensive to replace per some of the info I've read so be careful if you try to clean it!

[Phatdonkey78]

Originally Posted by firebird1999us

I had a similar issue but it turned out the alternator that I had recently replaced was not tightened down enough. I had cranked down the bottom bolt pretty tight but it was still not as tight as it needed to be. My mechanic got it on there tight and the car stopped a good bit of what I felt was mechanical vibration. I felt like I was in danger of overtigtening but I guess it had a bit to go.

My car has 350k+ on it... we also discovered through the whole process that the vibration I thought was an idle issue was actually the motor/transmission mounts failing. I was only getting a vibration when the car was in gear and I had the AC on at a stoplight when the car was under load. Now that we've pinpointed the mounts failing I can feel that the vibration is coming from the direction of the transmission and lower motor mounts.

There's also an Idle Control Valve that can be problematic too... I believe it's located under the throttle body? Those are fairly delicate and expensive to replace per some of the info I've read so be careful if you try to clean it!

Thanks for the info Firebird,

When I got the vehicle I needed to replace the alternator tensioning bar since the original was cracked on the top and was making the alternator sit at an angle making the worst belt squeal ever. When I removed the alternator it had rubber dust all over the side from the last belt being chewed up. So I know the alternator is nice and tight and charging the system as well.

The car belonged to my mother in law then my brother in law and I was their "mechanic" for the last 6 years. I replaced the motor mounts about 3 years ago around 145k miles so they are good as well.

When I did the throttle body cleaning I didn't see an Idle control valve like on older Toyotas I have worked on. I think since the TB for the yaris is throttle by wire, it simply adjusts the butterfly to make an air change at idle. When I cleaned the TB I didn't notice an IAC vent in the plenum.

Those would all make the vehicle feel like it is shaking for sure, but the only one I would think of causing the near stalling would be the TB. I think if the weather holds up I will remove it and clean it on both sides to see if a difference is made.

Thanks again!