I have a 2010 LS demonstrating a rough idle 10 to 15 minutes after starting (once it's warmed up).

My neighborhood auto repair place has replaced two sensors, along with spark plugs and spark plug wires.

Now they're telling me that >they< can't replicate it, they can't spare a mechanic to replicate the issue, and they can't spare a mechanic after >I< replicate it.

Anybody have any ideas why it would be doing this?

On a related note, anyone have an authority for what the idle RPM should be for it?

 

Get another shop, there aren’t any spark plug wires for one thing! Rough idle usually sets a code! What spark plugs did they install? Should only use AC Delco 41-103 iridium plugs.
Most times a good cleaning of the MAF sensor and the throttle body will clear things up. Do not use carb cleaner! CRC sensor safe and throttle body spray works great.
If your check engine light is on get the codes read and post just those codes any parts store should do this free of charge. Do not purchase any parts until we see those codes.
theres no adjustment to the idle, it’s computer controlled

 

Why did they replace parts? Was there CheckEngineLight?
Correct idle is around 700 RPM

 

There was a check engine light, but no longer

Codes were
P0171 O2 sensor in Bank 1
P1133 Another sensor of some type
P0300 multiple misfires.

So the plugs don't have wires or boots?

 

And we found the problem. The HHR has >two< oxygen sensors. It hurts nothing to change both when one goes out.

That was the reason behind both OBD codes - both sensors went out, one a little while before the other one (month or so).

 

You don't think it is important?
What were the codes? Get the car checked for codes again. Get it checked for "I/M readiness".
O2 sensors don't just "go out" with no reason. Especially the sensor after the cat, its only purpose is to monitor the health of the cat.

 

I would think that 129,000 miles would be enough for an oxygen sensor. I'm finding guidance to change them every 30,000 miles. My bad.

The error codes were suggesting two sensor issues (P0171 and P1133, which is proprietary). The shop assumed there was only one sensor, with two issues. With one upstream and one downstream from the catalytic converter, they should have both been changed at the same time. The shop just caught the second one and changed it. I'm test driving with a road trip tomorrow.

And the one after the catalytic converter is functional upon starting the car. The one upstream takes over when it's warmed up until the ECM indicates an emission condition that calls for recalibrating the fuel air mix. The reason for the P1133 was that the upstream O2 sensor was not working properly. Both error codes went away when the downstream O2 sensor was replaced.

And "I/M monitoring" showed on my OBD reader as OK IIRC. I'll check in the morning.

 

I think you’re gonna have that P0171 code again.

https://www.obd-codes.com/p0171

It’s telling you that there is a leak between the head and the upstream O2 sensor, possibly a cracked exhaust manifold, or the flex pipe is broken. Again I suggest cleaning the MAF sensor

The P1133 code indicates there’s an exhaust leak, or the wiring to the upstream O2 sensor is damaged . So that might not return

 

The #1 sensor (before the cat) controls the A/F ratio, it starts working when the computer goes into closed loop after the heater does its job. The #2 sensor has a heater in it but it is responsible for monitoring the health of the cat.
P0171 indicates that fuel TRIM is lean. Nothing needs calibrating, it needs to be addressed.
P1133 means that the #1 sensor is bad, If there are other codes it might indicate a fuse or wiring problem. Bosh brand sensors are famous for doing this.
The O2 sensors have heaters in them because they need to be hot to work and relying on the exhaust would take too long for the EPA.
The computer starts in open feedback loop then after the O2 sensors start working it goes into closed loop. In open loop the computer uses its presets to manage the A/F; in closed loop it uses the feedback from the sensors.
Whoever you are getting advice from is just trying to get into your wallet. I don't know why they should be replaced in pairs or as maintenance items; might have been true in the last century.
For a better understanding take a look at the free shop manuals via the link in my sig, or at charm.li.

 

P0171 is not a "sensor code." It's a fuel trim problem, possibly cured when you replaced the #1 sensor.

Cleaning the MAF sensor and throttle body was good advice from OldBlue. Also consider a bottle or two of fuel injector cleaner.