SafetyDave

Hey yall,

I have a 2009 with roughly 141000 miles and when in park and sitting at red lights I have a rough idle. Also, when going 40-45 mph my RPMs rev up and down like crazy. Any information would be greatly appreciated.

Oldblue

Any codes? You reported last October that you had a problem with the woolly worm hose disconnected, but that was resolved. You were going to clean the throttle body and the MAF .
is the MAF connection firm?
many timing chain noise?
any CEL light?
many possibility the fuel injectors are dirty?

PulpFriction

Scan for codes, even if no CEL. Check to see if the Woollyworm is still connected to the firewall. The grommet gets dry and shrinks a little and comes out easily with age. Double check that the MAF sensor is still connected. Have a look at the MAF sensor and the throttle body to see if they’re dirty again. Has this been going on for a while, or is it with a new tank of gas perhaps from a new source? You could try a bottle of fuel injector cleaner in your next tank.

RJ_RS_SS_350

We've heard many times about the 40 mph wander, which is normal, where the transmission is upshifting and downshifting, unsure which gear it should be in. Perhaps whatever is causing the rough idle(dirty TB, etc.) is exaggerating this normal wandering condition.

donbrew

Rough idle and stalling is what happens when you forget to plug the MAF in after a filter change. Could be a dirty throttle body.

KArthur

I have noticed mine doing the 40MPH bounce too. It also does this when its going into Overdrive. It does not do it all the time, but I have noticed that it is more likely to do it when it not quite to operating temperature. I have a scanner that I am going to connect and see what live data I can get.

donbrew

It is going to do that when going into overdrive. Every car I have driven with OD has.
The computer is in Open Loop until it gets to operating temp. That means it is working with standard tables instead of feedback from sensors.
Live data isn't going to tell you anything.

KArthur

When you say "Every car I have driven with OD has".... you mean every HHR with a 4T45e trans, right? Not EVERY car does this. I have driven a bunch of cars in my life with OD and this is the first one that does this.

It doesn't seem right to me.

PulpFriction

I thought it went into closed loop as soon as the O2 sensor got hot enough to work, way before “operating temperature.”

My long-gone 2008 LS automatic did this too. But only very intermittently. It would do it for a few week months and then not do it. I had done a few maintenance items that I can’t correlate to the behavior because I wasn’t paying attention to it; fuel injector cleaner in the gas, MAF sensor cleaner, throttle body cleaner. Maybe the behavior was due to wonky sensor data from dirty components.

donbrew

"Operating temperature" is when the O2 sensors are ready, not when the coolant reaches a certain temperature. Usually very near the same, especially when you know that the important temp in HHR is 158F not 180F.
What part of "that I have driven with OD" is not clear? That is pretty narrow definition. I did not say "All cars with a transmission". My Mazda does it, several Toyotas I have driven do it. a Nissan did it and both HHRs I have owned did it. It is because there is a clutch in the torque converter involved.