My car is doing a thing (and I would like it to stop)
July 24, 2012 6:04 PM   Subscribe

My car is doing something kind of alarming, intermittently. I'd love to get some guesses as to whether I need to see a transmission specialist or not before I take it somewhere.

(I have brought it to a transmission guy before, but it of course didn't happen while he was looking.) So what's happening is periodically, while accelerating, the car will slow down sharply, in a jerky fashion. The jerking stops the instant I take my foot off the gas, and usually doesn't come back immediately. The RPMs don't seem to change much while this is happening. It's been going on for probably a year or so, but has gotten more frequent in the last couple of months. The Check Engine light does not come on, and when I brought it in last winter to the transmission guy, he said there were no codes to pull. At that time he changed the transmission fluid and the spark plugs since it was time for it anyway. This didn't change the behavior at all. The only other unusual thing about the car is that occasionally it goes into a fast idle while parked - it's done this since I got it. (The car also seems to have less acceleration these days, but it's a four-cylinder sedan and was never particularly zippy, so I can't swear it's not just me.)

The car is a '01 Saturn SL1, automatic, with about 105k miles on it. It's generally been a good car - no real problems until now - but I am not afraid to take him out back and shoot him if this ends up being a major problem. I would rather not spend a ton of money trying to diagnose it (although I will definitely at least give it one more shot.) Anyone seen this before? Any particular tests or resources I should look in to? And does it look transmission-y? (My usual mechanic, whom I like but I am not too attached to, doesn't do major transmission repair.)
posted by restless_nomad to Travel & Transportation (12 answers total)
Are you near an Auto Zone? If you ask nicely, they'll bring their little diagnostic computer out to your car, run it and give you a printout of the specific error codes (if any) your car is throwing, totally for free. You will then have access to a wealth of info (some great, some crap) on Teh Internets. We've solved a few issues with our vehicles this way.
posted by julthumbscrew at 6:11 PM on July 24, 2012

Best answer: As julthumbscrew suggests, maybe try one of the Saturn forums. (I had a particularly not zippy '96 SL1. I had to turn off the air conditioning to merge onto the highway. No trans issues though.)
posted by Rob Rockets at 6:16 PM on July 24, 2012

If it helps, I had a not all that dissimilar problem on a 2001 Neon.

It ended up that I had blown apart one of the less important thingees in the transmission, and its bits had blocked some sort of fluid-movement port. So I would completely lose power, but just letting off the gas would instantly fix it, temporarily.

I took it to a friend I trust, who came back with that diagnosis, so I tend to consider it credible rather than a random repair shop screwing me.

/ Not a car surgeon - obviously.
posted by pla at 6:21 PM on July 24, 2012

I don't see any particular reason to think it's "transmission-y."

If by jerking you mean you get pushed forward and back and forward and back in your seat (while keeping your accelerator foot steady), a friend had this symptom and we found that the air intake hose had a tear in it. What happened was the acceleration made the engine move/twist, which opened up a gaping hole in the intake, which screwed up the operation of the intake air flow sensor (MAF). This made the engine lose power, so it rotated back into place, closing the hole, and had power again, lather/rinse/repeat.

(In his case an idiot at an oil change place tore it all up when pulling his air filter out for an attempt at an upsell, and then mashed it all back together and didn't say anything.)
posted by fritley at 7:14 PM on July 24, 2012

I would have guessed fuel filter for all of the symptoms except the "RPM stays relatively the same".

What happens if you shift into neutral when this happens?
posted by NoDef at 7:28 PM on July 24, 2012

This sounds pretty typical for an aging transmission. My 2000 Passat is just starting to do this @ 174K miles. It sounds like hard, difficult and hesitant shifting to me.

Like if you're at the end of 1st or 2nd gear and when it should be shifting it feels like a major hesitation or stall. (It usually happens in the lower gears when the trans is under the most stress.)

Considering that you've already had the transmission fluid changed, I'm going to guess that the trans is slowly failing.

I don't work on transmissions but I know how they work. Inside there maybe a dozen pressure plates, like clutch plates, that are activated by hydraulic pressure. If the hydraulics aren't the problem, then it's likely that the plates are worn to the extent that they aren't functioning properly. There are other things that may trigger gear shifting in an automatic, like vacuum or electronics, but if your car has been well maintained they probably aren't the problem.

As a stubborn bastard, I'd ride this out until it gets critical. In the mean time though, I'd be looking for a good/cheap rebuilt transmission.
posted by snsranch at 8:39 PM on July 24, 2012

Response by poster: What happens if you shift into neutral when this happens?

I have never tried - I'll keep that in mind for the next time it happens on an otherwise empty street. What would you expect it to do if it's a fuel filter problem?

Part of the reason I originally guessed transmission was that it seemed to happen most consistently while shifting into third. Now it's not that limited, but it's hard for me to tell if it's mostly around shifts because when it doesn't happen, the car shifts fine, and I'm never actually expecting it when it does. (And of course there's no handy gear indicator.)

The Saturn forums are pointing towards a valve body problem - it sounds like this is not an uncommon issue. But more input is definitely welcome, because a low-mileage forest green Saturn Sky just arrived at the local Carmax, and I *definitely* need to be talked down.
posted by restless_nomad at 9:11 PM on July 24, 2012

Best answer: I had a similar issue with my 2001 SL1 auto with 102,000 miles (Sylvia). It was not as dramatic as your problem; it manifested primarily as hesitations in second, especially when under load/hills, with a shift in engine noise to what I described as "rrrb--rrb--rrrb" rather than "rrrrrbrrrrbrrrrrbrrr". A throttle body cleaning aimed at correcting a low idle seemed to have the side benefit of ameliorating the hesitation, though I do not know how long-term that would have lasted or whether it actually did any more than mask the noise.

Unrelated! At 101,000 the PCM needed replacing, and at 102,000 the starter went out and there were Ominous Rattling Noises from the back end every time I drove it that made me concerned she was going to drop the muffler or the entire transmission the next time I went over a bump.

The throttle body cleaning was just a week ago, but I traded her in for a Mazda3 about 2 hours before you posted this question, so I can't tell you the long-term outcome. Had I known, you might have been able to get mine for spare parts (the starter still had 11 months on the warranty)!
posted by subbes at 3:12 AM on July 25, 2012

The question about shifting to neutral was trying to see if when you take the transmission out of the equation do you still have the same feeling.

Fuel filter problems usually result in a loss of power. A partially clogged filter can starve the engine of gas - it might be fine at low speeds but at higher speeds you could get sputtering. But this would also decrease the RPM.

But sounds like you have a good lead with the valve body issue...
posted by NoDef at 6:24 AM on July 25, 2012

This reminds me of an issue I had with my older car, where the catalytic converter had been damaged in some way that caused a specific range of speed to throttle the car a bit. They're expensive to replace because of platinum or something so I just ignored it
posted by MangyCarface at 7:01 AM on July 25, 2012

Response by poster: You have failed me! Failed me! My bank account may never forgive you.

But thanks for the ideas - it ended up looking like sinking 500+ dollars into a car worth $1000 didn't make quite enough sense, plus my dream car was on a lot 15 minutes away.
posted by restless_nomad at 1:55 PM on July 25, 2012

Ooooo, pretty car. Here's to many happy years!

Had Saturn not been taken behind the woodshed during the Automobile Massacre, I would only buy and drive Saturns for the rest of my life.
posted by subbes at 5:00 AM on July 26, 2012

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