Be still, Aztek, be still!

August 9, 2011 4:46 PM

My sister's new-to-her 2003 Aztek shudders sometimes.

The Aztek shudders in the first drive of the day when accelerating from a stop. It also shudders, now, at speeds between 60 and 80 mph.

The transmission fluid and filter were changed. A faulty speed sensor was replaced. What else should she look for? What can she look at herself, before taking it to a mechanic? She's on an out-of-town trip and would like the car to be more drivable on the way home.

Thanks!

posted by galadriel to travel & transportation (12 answers total)

IANAMechanic but shuddering at speed usually points at wheel balance or alignment issues.
posted by Skorgu at 5:15 PM on August 9, 2011 [2 favorites]

My guess is a stuck brake caliper. Wouldn't be strange on an 8 year-old car.
posted by InsanePenguin at 5:30 PM on August 9, 2011

If it's an automatic, I found this Technical Service Bulletin. She would need to take it to a Pontiac dealership to have it fixed, I believe.

Also, the two different instances of shuddering could definitely be unrelated. As Skorgu pointed out, the higher speed could be an alignment issue, or uneven treadwear on the tires.
posted by InsanePenguin at 5:36 PM on August 9, 2011

Crap. THIS
posted by InsanePenguin at 5:37 PM on August 9, 2011

Thanks so far! I'm also chatting on #bunnies and they asked for a few more details, and suggested I come back here and add them too.

They wanted to know if there were any problems with the brakes; she says they squeal a little at the end of a brake, sometimes, but the guy who looked at them said they didn't need replacing.

The shuddering on the first-drive-of-the-day lasts maybe 5 or 10 minutes only.

We don't know any really good local mechanics, but we can certainly take the car to one of the iffy ones we know to get the alignment checked tomorrow.

The #bunnies also told me to try depressing the calipers and see if they spring back to check if they're sticking; we'll try that when it's light out tomorrow.

Again, thanks! If there's anything else we can check at home we'd really appreciate it. She'll definitely look into the Technical Service Bulletin when she gets home, too...unless it's urgent enough that she should postpone going home and get it looked at here?
posted by galadriel at 5:50 PM on August 9, 2011

The high speed shudder sounds like wheel balance. A $20 balance service ought to take care of it.
posted by COD at 7:51 PM on August 9, 2011

Our minivan recently started shuddering when departing on the first drive of the day. It was diagnosed with a leaky head gasket--small amounts of coolant were leaking into the oil, which caused the shuddering on startup but which eventually burned off after the car was running for a while. Fortunately, adding a stop-leak product has staved off the problem for a while, because for our vehicle model, replacing the head gasket is a very costly affair. But I'm not knowledgeable enough about cars to tell you whether this is likely to be your problem, or the advisability of adding stop leak as a corrective measure.
posted by drlith at 4:51 AM on August 10, 2011

This is a good place to look for reputable mechanics near you.
posted by davemessina at 5:06 AM on August 10, 2011

It also shudders, now, at speeds between 60 and 80 mph.

If it always shudders between the same speeds for the whole time it is at those speeds (ie doesn't go away) then it may well be wheel balancing. Chances are it is unrelated to the other shuddering.

The Aztek shudders in the first drive of the day when accelerating from a stop.

'shuddering' is not a good descriptive term, unfortunately. We'd also need more information - does 'first drive of the day' mean that when the car is warm (in the middle of the 'normal' range on the temp gauge) the problem goes away? That's useful information. My guess is it's some kind of sensor that isn't compensating for cold load conditions (with it being through acceleration primarily). You'd need someone competent with a code reader/diagnostic tool at this stage unless you can find more symptoms.

What I'd do next is to try and make it do it worse or more repeatably. Is there a driving style that highlights it? If so, tell us what that is, that should help.
posted by Brockles at 5:44 AM on August 10, 2011

Also, get the wheels balanced. That will help the trip back.

(the shudder on accel could also be suspension or transmission, too, rather than engine. We'd need more info to find out for sure, but I'm not sure this is anything that she can address before she comes home. Get a breakdown recovery package just in case.)
posted by Brockles at 5:45 AM on August 10, 2011

If it's an all wheel drive version - check the rear drive shaft u-joints. They will shudder from a start.
posted by alfanut at 10:30 AM on August 10, 2011

Okay, we got the wheels balanced and the alignment checked. The wheel balance was off.

It's front wheel drive.

We drove around trying to duplicate the shuddering, and I tried to find out what "shuddering" means a little more precisely. We never felt it during the drive today. Here's what I think she means by "shuddering."

In the first drive of the day, it feels like it's shifting roughly when going more than about 15 miles per hour through about 40. It gives this feeling maybe a couple of times a minute, much more often than it would actually be shifting. It only happens the first time she drives the car for the day (even if it sits for hours between driving), and it apparently stops once she gets to 40-ish the first time.

On the highway at speeds between 60 and 80 it felt like it was shifting every 30 seconds to a few minutes apart, or sometimes it would go "a while" without happening.

I had a car once that felt like it'd downshift then shift back on occasion, and it was a clogged fuel filter. Should I get her to have that replaced before she goes home? Is there anything else it might be?

Thanks again for all the help!
posted by galadriel at 1:48 PM on August 12, 2011