What could have been removed from the engine compartment?
May 2, 2010 3:30 PM   Subscribe

What part could you remove from a car engine that would suddenly limit power to 3000RPM?

Left the car with a valet a few nights ago, and on return my engine light was on but the car was drivable. I was on local roads, so I didn't need to push the engine so hard so I didn't notice anything weird. The next day I am driving and as soon as I hit 3000RPM in any gear the engine just gives out and I need to move down a gear to get it moving again. No loss of power, it just goes limp and I need to bring it under 3000 to get acceleration again.

My suspicion is that the valets popped the hood and pulled something out while they had the car because this was no gradual change. Car was perfect before this and all of a sudden this transmission problem immediately when the car was delivered.

The question is, is this a telltale sign of the removal/failure of any part in particular or does it sound like a general transmission problem that just happens? Going to the mechanic this week, but I wanted to see if this is anything obvious to the more car knowledgeable.

Model 2007 Audi A3 1.8T w/ tiptronic.
posted by lovejones to Travel & Transportation (19 answers total)
Anything you could pull out relatively easily would either make the car undriveable or cause some other symptom besides this one.

My guess is that the ECU needs to be replaced or flashed.
posted by Cool Papa Bell at 3:35 PM on May 2, 2010

A guess, possibly stuck in valet mode which limits power.
posted by hungrysquirrels at 3:44 PM on May 2, 2010

Sounds like compression problems. I'm not familiar with that car, but I have a hard time imagining that a stolen part is the culprit.
posted by 256 at 3:45 PM on May 2, 2010

Your line of thinking is way off. There are a million things that could cause this problem. My guess is that there is a computer problem. If it is valet caused it is more likely from them redlining it while you are inside than stealing something. I say this as a former, albeit briefly, valet.
posted by nestor_makhno at 3:53 PM on May 2, 2010 [1 favorite]

I'd bet money that it's in some sort of valet mode. Did you give them the valet key? Are *you* using the valet key?

There's nothing in a car whose removal will limit the RPM to 3k consistently, while leaving the car operational. Nothing. I mean, you could reflash the ECU. But they didn't do that at the valet stand. Pulling the turbo wouldn't even do this. Nothing.

What does your manual say about it? You've read your manual, right?
posted by Netzapper at 4:01 PM on May 2, 2010

Oh, wait. Your check engine light was on? Well why the fuck didn't you take it to even a Jiffy Lube and have them scan the code?

That light is your friend. It's telling you something is wrong.

Even still, they didn't steal any engine component. The ECU is just doing you a favor and limiting your engine speed on what may be a malfunctioning engine. Did you put low-test gas in your turbo-charged car? Leave the fuel cap loose? Go get it scanned... they'll usually do it for free at Pep Boys and the like.
posted by Netzapper at 4:05 PM on May 2, 2010

Googling found no evidence of a "valet mode" in Audis, but I might be wrong here. My bet is that the valet drove your car hard, screwed something up, and triggering a safety mechanism in one of the car's computers. It could be a simple clutch problem, triggering some anti-slip software, or it could be a sensor problem -- the MAF sensor is my guess .
posted by spiderskull at 4:09 PM on May 2, 2010

Oh, yeah, follow Netzapper's advice -- take it to a mechanic ASAP (I'd avoid Jiffy Lube...)
posted by spiderskull at 4:10 PM on May 2, 2010

More than likely the motor is in "limp home mode". This Wikipedia article on electronic throttle control has more info, but the short answer is what was said above: you need a code reader to pull the code and see why the computer is in a failure state. Most AutoZone and similar retailers will do this for free.
posted by mosk at 4:27 PM on May 2, 2010

As Netzapper and mosk said, the check engine light is the car's way of notifying you that a self-diagnostic test failed. There is a code stored in the computer that will usually tell you exactly what's wrong. Some auto parts stores will read the code for you, or just take it to a mechanic. Mosk is also probably right about the car being in limp home mode. It's a self-preservation tactic to keep you from driving the car hard until the problem is resolved.
posted by knave at 5:12 PM on May 2, 2010

It's a self-preservation tactic to keep you from driving the car hard as if it were a nice car that you don't pay for maintenance on until the problem is resolved. FTFY.
posted by flabdablet at 5:19 PM on May 2, 2010

Valet Mode on Audi's is usually something you get when you re-program the chip; it's not a factory default.

Take it to the dealer. Something is wrong in engine land; perhaps the coil pack, perhaps something else. If the engine light starts (or was) flashing, stop driving and tow it to the dealer.
posted by jeffamaphone at 5:19 PM on May 2, 2010

Mosk is on to something - lots of sensor diagnostics force default actions like limp home or forced idle. The severe ones shut down the engine. The valets could have unplugged a connector underhood. If the check engine light is blinking, indicating misfire, or it just runs really rough, follow jeffamaphone's advice.
posted by rfs at 6:15 PM on May 2, 2010

I'm in Mexico City, and unfortunately it's not uncommon to get things pinched by valets. I was just wondering if it was getting more sophisticated than the ipod in the glove box level stuff. No offense to the upstanding valets out there.

You guys must be right about the computer limiting the RPM, its the only thing that makes sense (and I saw nothing about valet mode in the manual). I didn't even know that existed. I just want to be prepared when I go into the dealer, in case it was anything blatantly obvious.

Taking it to the dealer tomorrow, thanks for your help!
posted by lovejones at 7:47 PM on May 2, 2010

Wild guess, but if the engine is limping with a code, I would check that all the spark plug wires are connected, that the O2 sensors and catalytic converters are present and operational (and the mass airflow sensor, too).
posted by zippy at 9:48 PM on May 2, 2010

My Audi A6 has a valet key for this purpose. If you can get a hold of a VAGCOM, you could see if the ECU has thrown an error. I keep one in the garage so that I don't get any surprises when it goes in for a service.

My Skyline GTR also has a 'limp home' mode that activates when you come into some money unexpectedly (e.g. get a raise, tax return, etc). It's meant to be caused by running rich, boost problems or some other sensor failure, but I know better.
posted by Sutekh at 12:29 AM on May 3, 2010

There are a few possibilities, but you HAVE TO SCAN the computer. Valet mode typically won't turn the check engine light on, either.
What's MOST likely is that a key or light was left on and the battery went dead. When the battery dies or system voltage gets too low, certain problems occur, most notably the electronic throttle adaptation needs to be reset.

This is very common on VWs and Audis. You'll need to take the car to a shop that has a factory level scan tool like the Vag-COM mentioned above.
posted by Jon-o at 4:21 AM on May 3, 2010

You are definitely in "limp home" mode. The reason could be many things. Failure of the MAF is a prime candidtate. You definitely need to get it to a good mechanic...either the dealer or a Bosch-certified shop.
posted by Thorzdad at 5:19 AM on May 3, 2010

What everybody else said. VW's 1.8T can be a temperamental engine.
posted by schmod at 7:39 AM on May 3, 2010

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