They see me rollin' / They hatin' / 'Cuz the limit's forty-five and I'm drivin' twenty
June 16, 2012 11:01 AM   Subscribe

My car, it acts... strange. What's wrong with it, and what am I looking at to fix it?

I've had three incidents in the last two months where my car has gone weird on me. Before I take it in, I was hoping to get some idea of what may be wrong with it and what I can expect to spend fixing it.

What it's doing: On acceleration from a stop (not from engine ignition, from some seemingly random point mid-trip), when I hit twenty mph, the engine revs high for about a half-second, then makes a sound of acceleration that I can best describe as "woo-woo-woo-woo." It kind of sounds like a dubstep beat. The speedometer fluctuates between 20 and 25 mph. Giving the car enough gas to maintain 20-25 doesn't change the status; giving it more gas likewise doesn't change the status. Letting up on the gas and then SLOWLY reapplying the gas will sometimes get me past 25, but if I press too hard it will repeat at 25-30, 30-35, etc.

How I've managed so far: The solution to this has been pulling off the main drag (where this always happens, natch) onto a side street, and cutting the engine. Waiting about 30 seconds and then restarting fixes the problem, and I can proceed on my way without incident.

The check engine light comes on when this initially happens and then for subsequent restarts of the car, but after two or three starts, it goes away.

What is the car: 2005 Dodge Stratus with automatic transmission.

What I know about cars: I occasionally put shampoo instead of gas in the tank if I'm not paying attention.

Why I haven't had it looked at yet: Bills, son.
posted by Golfhaus to Technology (12 answers total) 1 user marked this as a favorite
Dodges have a limp mode when the car decides that it can't be driven normally and goes into 1st or 2nd and won't shift out. As you've noticed it also disconnects the accelerator so you can't rev the engine. It's designed to let you "limp" home slowly if the engine is damaged or something is wrong and to protect it from catastrophic failure. From what I've heard it can also get "stuck" in limp mode for electrical reasons when there's nothing wrong with the engine. This happened to a friend of mine last year, some fairly minor wiring or sensor problem had his car suddenly stuck at 25mph on the highway 250 miles from home. He wasn't happy!
posted by fshgrl at 11:52 AM on June 16, 2012

You can take your car to AutoZone and they will find out what's triggering the Check Engine Light to come on -- for free!
posted by Houstonian at 11:53 AM on June 16, 2012

That sounds to me like what happens when the computer detects a serious problem that could damage the engine and puts the engine in "limp-home" mode. I'd check on the Throttle Position Sensor and the linkage between the accelerator pedal and the TPS first. Dodge transmissions of that era are also known to have relay problems that put the transmission into limp mode.
posted by ob1quixote at 12:00 PM on June 16, 2012

Have the trouble codes read as Houstonian suggests. These will give you a starting place. There are just too many things that could be wrong in this case to make a diagnosis without the codes.
posted by Thorzdad at 12:12 PM on June 16, 2012

This really does sound like limp home mode. This can be when the ECU loses a crucial sensor reading and it doesn't know what the engine is doing. It assumes the worst and just limits the rpm to something low. I think something is causing the car to 'trip' to fail safe mode and an ECU reboot is resetting it until the next time it loses the setting.

My car (Jaguar, but relevant) did this when the throttle position sensor failed. It could be expensive or minor but the only way to know is to read the engine fault codes and get it diagnosed, I'm afraid.
posted by Brockles at 12:55 PM on June 16, 2012

I had a similar issue, it was the transmission - needed full replacement/rebuild.

I don't know much about how it works, and this was a few years ago, but the gist was that there was a crack somewhere that would expand when the engine was warmed up and not allow pressure buildup, so the car couldn't switch gears easily. Allowing it to cool returned it to normal operation.
posted by Sonic_Molson at 1:27 PM on June 16, 2012

What's the tachometer at? Are you redlining it and it is hitting the gas cutoff?

If not, chances are really good that you have a problem with ignition. If you floor it from a stop, what happens? If it tries to die out, then that's probably what it is. The check engine light will also probably be flashing.
posted by gjc at 4:53 PM on June 16, 2012

Response by poster: Thanks, everyone - this deal about "limp" mode sounds like a perfect explanation for what's going on. My wife (who was the primary driver of the car until I took it over a couple months ago) points out that we've had some electrical issues with the car.

gjc, IIRC, it's around 2000-2500 rpm. Not redlining, I'm too old for that crap. I haven't tried flooring from a stop, as this usually happens in city/suburban traffic patterns and I'm not in a position for experimentation.

Question - right now, the Check Engine light isn't on. My understanding is that this isn't supposed to happen, and that the light is supposed to stay on until someone triggers it to say "a qualified person has figured out what's going on." Since the light's off, though, if I were to get in the zone at AutoZone or a similar place, would they still be able to determine what is triggering the light? Is there a "last code generated" feature?
posted by Golfhaus at 5:34 PM on June 16, 2012

Hmmm. Maybe, maybe not. It is possible that the code has been cleared if the light has gone out. I've chased faults before that never NEVER GODDAMN IT show up when I have a code reader with me. I now have one on my iphone that I can interrogate the car with and then email it to myself for the records:
posted by Brockles at 8:31 PM on June 16, 2012 [1 favorite]

For a 2005, there's a completely decent chance the code is logged and the car will report the last code to trigger limp home mode. AutoZone, et al, will do a code read for free. It takes literally 30 seconds as they plug their OBD reader into your car and tell you what the story is.
posted by disillusioned at 3:19 AM on June 17, 2012

That sounds exactly like a problem I've had with two different Dodge Neons. I don't know cars very well, but I know the Stratus has some design similarities, so I explain as much as I can remember from my mechanic's explanation.

There's a part (valve, gear, I don't remember) between the accelerator pedal and the transmission that can get "stuck." When it's stuck, accelerating too quickly ("flooring it") causes the transmission to make the "woo woo" and stay in low-speed mode. Pulling over to the side of the road and shifting into and out of Park will get you back to normal.

If that's your problem, the good news is that the transmission itself is fine. The bad news is that (on a Neon, anyway) reaching the stuck part requires dropping the transmission, so you still have a pay a couple hundred bucks for somebody to unstick something that may get stuck again in six months.

(In situations like this, I find it helps to quietly remind myself "Mopar or no car!")
posted by faster than a speeding bulette at 9:25 AM on June 17, 2012

Our 1995 Plymouth Grand Voyager did this, too. It sure sounds like limp mode, and from what I've read about it, it's a common problem with the transmissions they put in 90's Dodges and Plymouths. In fact, your car should have the same transmission our van did. Here's a page about the problems that hateful little bit of machinery had.
posted by clorox at 6:02 AM on June 20, 2012

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