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2006 PT Cruiser idles rough and shakes b/t 50 and 60 mph

Hi Car Talk Community,

I have a 2006 PT Cruiser with approximately 94K miles on it. This year I started a 2-hr round trip commute every week day, so the car went from getting ~200 mi. a week on it to ~700 mi. a week. I bought it used ~4 years ago with 28K mi. on it.

2 months ago, the car started shaking between the speeds of 50 and 60 mph. Not sure how to best describe it - kind of a shake/jerk, like someone was jerking the car forward very quickly and repeatedly. It seemed to be strongest in the front of the car on the passenger side, although you could feel it throughout the car. I took it to a repair shop. They balanced the tires, but that only very mildly helped. Then they changed the front axles (said there was a lot of play in them). They replaced the brakes, rotors, and timing belt at as well, for unrelated reasons. With new front axles, the shake disappeared, but the car has been idling incredibly rough ever since I got it back. You can see the steering wheel vibrate and feel it in the seat when I start the car or am stopped with it running. This never used to happen.

Additionally, the shake has now returned, but from the driver’s side of the front of the car now. Again, it’s between 50 and 60 mph, although it’s slowly creeping up into the 60-65 range also. It’s stronger if I’m pushing the gas down more, like when going up a steep hill. If I’m going downhill at 50-60mph, I don’t notice it or barely notice it. On flat ground it’s noticeable, uphill it’s becoming severe.

Any ideas on what could be wrong? The repair shop I go to is excellent and treats me well, but they had trouble figuring this one out. If I can go back with some suggestions I’d feel much more comfortable.

Thank you very much for any help/suggestions! Please let me know if more info would be helpful.

It sounds like the shake/jerk problem could be cause by a slipping torque converter clutch (TCC) in the transmission. The TCC is an electromechanical clutch that “locks up” the torque converter at highway speeds in order to improve gas mileage. If the TCC begins to slip, you’ll typically feel it as a “shudder” in the drivetrain beginning around 50 mph, and it will worsen with more load on the drivetrain (e.g. ging uphill).

Sometimes TCC slippage can be solved simply by changing the transmission fluid and filter. I would try that first since it’s inexpensive routine maintenance. I had similar symptoms due to severe TCC slippage in my van, and just changing the fluid and filter solved the problem.

But if that doesn’t do the trick for you, the TCC itself might need replacing, which is expensive. Cross your fingers and hope that a transmission fluid and filter change does the trick.

The rough idle may have a different cause, possibly a bad idle air control valve (IAC) or Mass airflow sensor (MAF). Sometimes the MAF just needs cleaning. A good mechanic should be able to diagnose the idle problem.

Thank you very much for the thorough explanation! It’s a huge help.

One quick follow-up question. The shaking is only present between 50 and 60 mph. I routinely drive 64/65mph and above on my commute to work, part of it is 65-70mph up a mountain, and the shaking disappears when I make it to the low 60s. It doesn’t feel like the car is shifting at all between 60 and anywhere in the low 60s. Could the TCC still be the culprit?

Thank you again!

i don’t know why the shaking would disappear above 60 mph if it was the TCC…but I would still put that on my list of suspects. You described it as a “jerking forward” feeling for which there are few other possibilities.

Other tbis might be a bad ignition coil, but usually tha’s not speed dependent. The TCC is speed dependent in the sense that the TCC usually engages around 50 mph, so if the TCC is failing you won’t feel the jerking below 50 mph or so.

The key question is whether the shaking/jerking is side-to-side or front-to-back. If it was side-to-side, I’d suspect suspension or steering components, but you said it was a forward-type of jerking, which suggests a tranmission problem (TCC) or perhaps an engine misfire. But again, I don’t know why you’d have an engine misfire only in the 50-60 mph range.

So my money is still on the TCC.