Death car, dumbass, or both?
January 20, 2011 3:35 PM   Subscribe

Did the guy who did my oil change break my car, or is this a fluke?

I drive a 2001 Ford Focus SE. It was a great car up to about 65-70,000 miles but the past 10k has plagued me to no end.

I took it for what I thought was a little nothing of an oil change today. I just went to Valvoline, had them do it there. In, out, no problem, not even an attempt to upsell me on things I don't need. After that, I drove about 2 miles into town, stayed there about 4 hours, then headed back toward home (about 2 miles).

When I started backing out of my parking place, my check engine light went on. Nothing felt wrong, but I headed back to Valvoline to have them check the code and figure out what on earth they broke. I mean, come on, it's 2 miles since they changed the oil, it must be related, right?

Once I got there, they read a code that I didn't get to see, but told me it was a "bad mass" and had messed up my fuel/air mixture. I take it that they were referring to the "Mass Air Flow" sensor, doing some research - so the code was probably P0170 or P0171. Guesswork, here.

The guys there both insisted it was a fluke, wouldn't have had anything to do with the oil change, and I'd just have to take it to a mechanic. I'm skeptical.

To complicate matters, the car promptly stopped running well once I tried to leave. Stalled out 4-5 times just trying to shift into drive, and again several times on the road. Even when it wasn't stalled, it jerked all over the place - acceleration was about .5 seconds on, .5 seconds of nothing, over and over.

Suffice to say this car is the farthest thing from safe to drive, and I'm pretty sure it's their fault. For those who know enough about cars to say, is it possible (likely?) that they broke something, or is this really a fluke? If they broke it, what should I do?

tl;dr Can an oil change and general fluid checks/poking and prodding break a Mass Air Flow sensor?
posted by Rallon to Travel & Transportation (15 answers total) 1 user marked this as a favorite
Check the intake tube from the air filter to the MAF. It's either broken or they didn't put it back on right when checking your air filter.

I had the same thing happen to my wife's Mazda after an oil change. They broke the intake tube IN HALF. I went odwn there screaming and yelling and they said it happens frequently and replaced it that day with no trouble.
posted by Big_B at 3:43 PM on January 20, 2011 [6 favorites]

Oh and the MAF itself is probably fine. On our car the tube broke downstream of the MAF, so the computer was unable to give the engine the fuel it needed becuase the MAF indicated very little/no airflow.
posted by Big_B at 3:45 PM on January 20, 2011

I'd take it to a certified mechanic I trust and ask them to check/inspect it, and give me something in writing to see what they find. My reasoning is simply to have someone with expertise look at it and have leverage in the far off chance you need to go after the oil change place.

It could be a fluke, it could be they didn't put your air filter back in correctly, they could have broke something. Go find out.
posted by Mister Fabulous at 3:50 PM on January 20, 2011

I would follow Big_B's advice first. Checking the intake tube should be easy enough, even for a novice. It does not really take a lot to break a MAF sensor, but that seems unlikely during a regular maintenance check.

Your next step, assuming you don't take it to a mechanic, is to see if you can get the sensor codes. It's odd that they wouldn't tell you the codes, especially if they haven't cleared them or if they're going to be repeated the next time you start the car. Many auto-part stores will loan or rent you a code reader, and many cars have a way to discover the codes without a reader, though it's kind of tedious.

By the by, if you have space to store the few pieces of equipment you need, you should seriously consider changing the oil yourself. Once you have the tools, it's not very expensive or difficult, and no hassles with the upsell or some highschool kid breaking your car trying to find more stuff to sell you.
posted by Hylas at 4:07 PM on January 20, 2011 [1 favorite]

The same thing that happened to Big_B happened to me, on a Mazda even. The shop I took it to changed my oil and then when I went about a mile down the road it stalled out and the check engine light came on. I cranked it back up and turned around and when I got back and popped the hood the intake tube was completely detached, as in, just kind of hanging there. They quickly fixed it and I went on my way.
posted by julie_of_the_jungle at 4:52 PM on January 20, 2011

I took my car in for an oil change once, and they drained the oil but "forgot" to replace it. A couple of days later the car broke down and the mechanic said it had been running with no oil and that [some mysterious part of] the engine was irretrievably dead. I still don't entirely know if I understood or believed what the mechanic was telling me, but maybe it's a datapoint.
posted by lollusc at 4:57 PM on January 20, 2011 [1 favorite]

I have been told that in California, if you change your own oil, the oil places are obligated to take it from you. I understand they are happy to, since they sell the old oil to be recycled.

As far as running bad after an oil change, yeah it's likely they knocked something loose or didn't replace/reattach it properly. Some places are great about "oh yeah, sorry about that, here, it's fixed!" and some places are "it's not our problem". Sounds like Valvoline there is in the latter category.

If they forget to put oil back in - and I have heard of that happening, in addition to lollusc's story - you won't notice anything wrong right away, though an oil light should come on.
posted by Xoebe at 5:58 PM on January 20, 2011

Does Valvoline sell or repair the thing they broke? If not, they are probably just morons.

Take a look at the engine, look for plugs that are disconnected, in the area of the large tube that goes into the engine. Look for cracked things.
posted by gjc at 6:05 PM on January 20, 2011

Seconding Hylas and lollusc. Jiffy change shops are the fast food equivalent of the mechanical world, and the minimum wage pay doesn't bring the talent. Or dexterity to not overtorque drain plugs. Or not crash into every sensor and tube/pipe under the hood. / rant.

Big_B seconded. They probably wacked something loose. Oil changes are not rocket science.
posted by buzzman at 7:54 PM on January 20, 2011

IANAM; Lots of good advice about the MAF - google says on your car it is located basically right on top of the air cleaner cover. I would pop the hood, inspect this item on top for broken or loose wires, tubes, or anything, then I would pop off the cover and take out the air cleaner for inspection, as well as inspecting the housing it sits in, to make sure they didn't leave a rag or something laying in there that's blocking airflow somehow.

If something is mechanically wrong with the sensor, I guess it's possible that something they did damaged it, but getting them to own up to it and fix it is probably not worth the hassle.
posted by SquidLips at 8:18 PM on January 20, 2011

The Mass Air Flow sensor in the car measures how much air is going through at the sensor. It's typically located near the air filter. The sensor tells the engine how much air is flowing past it, and the computer can adjust fuel, etc. to compensate. However, if there is a break in the intake tubing after the MAF sensor, air will get sucked in through that point. (A break can mean a crack in the intake duct, or a loose or disconnected intake duct, anything where air can easily flow.) If your engine is sucking in air from somewhere past the sensor, the MAF can't read that air since it's not flowing past it. What this means is that the engine is still getting air, but the air it's getting isn't being accounted for correctly. The MAF will report far less air than is actually going into the engine, and the car's computer will adjust accordingly. Which means the car will run like crap. So, if you do get a code that indicates a fault with the MAF, check for breaks in the intake duct after the air filter, and also see if the wires going to the MAF got knocked loose somehow. Those are the obvious things to check. MAF sensors very rarely fail on their own. They may have also gotten the sensor dirty, but that's something you may want to have a mechanic (different one obviously) clean, because this can be an expensive part.
posted by azpenguin at 10:25 PM on January 20, 2011

Nthing Big_B's suggestion, as the same thing happened to me, too.
posted by telophase at 12:08 PM on January 21, 2011

If you have to clean the MAF sensor, you can do that yourself, but consult google to find out how. The last time I cleaned the MAF sensor on my old Chevy Blazer (RIP), it involved spraying a specialized and probably toxic-as-hell chemical solution until it was clean.

As a lawyer, I've had two cases in which I had to contact an oil change place for something like this. You shouldn't have too much trouble if they broke a part--just call the manager or, failing that, go above him to a regional manager or to corporate. Good luck.
posted by Hylas at 1:49 PM on January 21, 2011

P0170 and P0171 are codes referring to the air/fuel ratio being too lean. That is, for all of its efforts (like increasing fuel injector output) the engine control unit can't bring the fuel ratio back into the specified range it is programmed to prefer.
Most places check for service items, like checking the condition of the engine air filter. Sometimes, it's an up-sell and other times, it's a genuine recommended maintenance. If they disturbed the air inlet ducting and didn't reinstall it correctly, it's possible that unmetered air is entering the engine and causing it to run poorly. If the engine computer doesn't know how much air is coming in, it can't deliver the correct amount of fuel and the engine will consequently run rough (or not at all).
Other things like broken vacuum lines, a dipstick left out, or a oil cap left off can create a way for unmetered air to enter the engine. Typically, a dipstick or oil cap type leak won't cause the car to stall. It might idle a little rough or sound louder than usual and even set the check engine light. However, stalling is indicative of a very large and significant malfunction.
Further, it's worth checking to make sure that they didn't accidentally overfill the engine with oil. In some systems, it's possible for an overfilled engine to draw oil into the air intake through the system that's originally designed to draw vapors out of the engine crankcase. That excessive oil can, in some cases, contaminate the Mass Airflow Sensor and it will under-report the amount of air entering the engine.

So, some of this stuff you can check yourself. Open the hood and check for obviously loose, broken, missing, or otherwise damaged or irregular components. Check the oil level, also. If nothing turns up on your search, take it to a good mechanic. Check out the Car Talk Mechanics Files or for great mechanics in your area.
posted by Jon-o at 5:18 PM on January 21, 2011

Response by poster: Much obliged for the answers from everybody! In the end, I decided this was the last straw with this car, whether their fault or no, and yesterday went ought and bought a lovely little used Honda Fit still under warranty. My dear, once-beloved Focus is now the problem of the dealership.
posted by Rallon at 5:23 AM on January 23, 2011

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