I’m not sure what is wrong with my car. I am putting it out to the wisdom of this crowd.
I drive a 2014 Chevy Spark with a manual transmission. It has ~102,000 miles on it. Through July I routinely get between 35 to 38 MPG. All of a sudden this changed.
Within a 2 week period, three things started to happen.
- Mileage declined to 15 to 18 MPG
- My speedometer does not register a speed when my foot is off the gas pedal.
- The car will intermittently stall when my foot is off the gas pedal in 1st gear.
Since then I have taken it to 3 mechanics 4 times.
Mechanic 1 thought it could be a mass air flow sensor problem. I replaced that on my own. It seemed to run a little better but no obvious change to mileage or stalling.
Brought it back to Mechanic 1. They then thought it might be a transmission issue so they referred me to Mechanic 2 who only does transmissions.
Mechanic 2 could not isolate a transmission problem.
Mechanic 3 is the dealership. They replace the manifold air pressure sensor.
This was weird. Coming out of the dealership, my mileage is back into the low 30s and the car runs smooth and idles fine. It does not stall for a week.
However, within a week, as classes started, my mileage is creeping back down to the low to mid-20s and it is a flip a coin possibility that the car will stall in first gear with no gas.
I really don’t want to put significant money into repairs as I’m a grad student and I don’t have significant money but if there are fixable things that mainly involve an afternoon and frequent swearing after my third run to Advance Auto Parts for a goddamn tool that I should have gotten the first time, I can do that.
Just Some Fuckhead
Had an agency minivan with similar symptoms. Turned out to be the catalytic converter.
To be Frank
I’m surprised you haven’t gotten an engine light and some internal code to help pinpoint the problem. It sounds a bit crazy, but have you changed the oil? The internal controls will cut power and take other actions to prevent the engine from self destructing if there is an issue (which usually also comes with the engine light coming on, again I am surprised). Low oil pressure or some other oil issue may be making the engine have issues. Since it’s a manual, I don’t see how the transmission can have any connection to your problem. This all sounds like a fuel delivery problem. I would also have someone check the fuel pressure, it could be an intermittently failing fuel pump.
Did symptom 2 disappear after the dealership replaced the sensor?
fuel pump maybe. Similar symptoms happened to our car.
Do you have a check engine light on? I imagine the answer is no, otherwise you would’ve mentioned that. *If* you do, go back to AAP and have them plug the code reader into the port to see what comes up. My initial thought is that the spark plugs probably need to get replaced. Plugs needing to be replaced wouldn’t necessarily bring up a CEL code, so maybe that’s it? Hopefully it’s just that. I’m sure that the mechanics thought of that already, though.
Or fuel filter?
The difference between me and a mechanic is I’m great at replacing parts, a mechanic is supposed to be good at fixing problems. You pay a mechanic to fix your vehicle, not replace parts that aren’t broken. When you find a good one, you treat them like a King.
As far as your vehicular difficulties, fuck if I know.
Any OBD2 scan codes? A reader is $20 and up. There’s a lot of information that the computer keeps track of that might offer some pointers. A good mechanic should check that first, and presumably already did so (but might not if the check engine light wasn’t on).
It sounds like several things are going on at once. Bad ground somewhere for #2?
“Fuel, Air, Spark”. EGR valve? Fuel filter? Mice nest in the air filter? Really bad tank of gas?
A clogged cat might be an issue too, but I don’t know how you can check that without replacing it.
Remote diagnosis is hard. Hope this gives you some more things to check.
Gin & Tonic
@Jerry: There are inexpensive OBD readers that you can plug into the port full-time and read via a Bluetooth connection to your smart phone, while you are driving. You can get a lot more diagnostic data that way. I think I paid ~$40 for mine.
ETA: The Spark is a shitty car.
Owner forums are often great resources: https://chevysparkforum.com/topic/6023-2013-chevy-spark-lt-speedometer-drops-to-0-when-letting-off-the-gas/?do=findComment&comment=33054
Yep, I have one in the glove compartment of my car. They’re great to have, for sure. I just mentioned the alternative in case Mr Mayhew didn’t already have one of his own.
If you own an older, car I highly suggest that you get one. As Gin & Tonic mentioned, they are not expensive. $40 is what I paid for mine as well and it’s an all in one unit, no need for any other device and bluetooth connections. Of course, you can spend a lot more for them and get more detailed information on a code, but I like my cheapie well enough.
@DemJayhawks: Great find.
And bad news. :-(
The mechanics should have found that for David before they started replacing parts. :-(
Too bad Car Talk is no longer on the air.
The bad news is we’re all guessing and haven’t really taken a look at the car the way three different mechanics have, and unless it was throwing a code they should have all checked the fuel pump / filter / spark plugs first thing.
The good news is that replacing the manifold air pressure sensor seemed to do the trick, so either it was a bad part (and should be under warranty from the dealership) or something in the electrical system is sending too much current to it and causing it to fail (which is back in the bad news category.)
Would explain why the cat hadn’t been taking care of the mice nesting in the air filter.
(Don’t know shit about car engines. Looking forward to EVs where you don’t have to have a miniature power plant under your hood.)
The mix of symptoms make it difficult to diagnose. I was struck in particular by the speedo behavior. This might indicate insufficient voltage when the engine is not under load (acceleration). Given the Engine Control Module (ECM) controls engine performance and can also suffer under insufficient voltage, I’d check everything involved with generating and distributing electrical power, from the belt that runs the alternator to the ECM itself.
The mix of symptoms make it difficult to diagnose. I was struck in particular by the speedo behavior. This might indicate insufficient voltage when the engine is not under load (acceleration). Given the Engine Control Module (ECM) controls engine performance and can also suffer under insufficient voltage, I’d check everything involved with generating and distributing electrical power, from the belt that runs the alternator to the ECM itself. Seconding the suggestion of an OBD reader, though your mechanics if they’re worth a salt already went that route.
@lowtechcyclist: If the cat was too busy clogging to catch mice, wouldn’t the music be audible?
I like the idea of getting constant error code readings while driving. This would have helped me with multiple car problems in the past. I’m still not sure why this isn’t simply built into internal combustion cars to begin with – along with the option to have virtual gauges.
When you watch the tach, is it working OK? Are you able to take it over 3k rpm?
@Rusty: Oil changed 1st week of August.
@Math Guy: No change in the speedometer symptom.
@Dan: Yeah, tach is fine. Gear shifting is fine, it runs good in 2nd through 5th gear.
Whst Scott and G&T said about diagnostics, you probably have more time and motivation to analyze the results than your mechanics.
But also, second MFA at #17. The speedo seems like the canary in the coalmine here,
Advice from Mitt Romney and his ilk: “What, you don’t have a second car? We always keep a spare in the garage in case the Bentley needs servicing! Just cash out those stock options!”
Wiring to the manifold air pressure sensor or reasoning for the sensor to fail
If it’s the bearing/reluctor transmission issue that Demjayhawks found, KBB says that it’s around $4500 to replace the transmission. Repair should be less, if you can get the parts, but you’re still looking at a lot for labor… :-(
Now is a bad time for buying cars in general, but you can still get decent ones if you look around. (E.g. 2014-2015 VW TDI with less than 100,000 miles.)
That user forum link at #11 does seem relevant.
Fuel delivery could be a problem and as DemJayhawks sez, owner forums can be helpful.
I’m off to the salt mines.
@Matt McIrvin: [Whoops. Misread your “does” as “does not”. Not enough caffeine!]
You might have to scroll down. It seemed perfectly on-point to me.
Sensor in the transmission fails, speedometer stops working. Computer doesn’t get speed information it needs, messes up the mixture, etc., and mileage goes to pot. It’s one of the first things that should be ruled out. (Apparently the ABS sensors can be used as a backup, at least to certain speeds – see his followup about disconnecting the cable from the transmission sensor.)
Trouble is, if the transmission sensor failed for the reason he cites – a bearing failing causing a seal to fail – then additional failures may be in the future.
But, we’re all just guessing at this point. The OBD2 codes may help (e.g. show if the computer is getting the correct speed information from the transmission sensor).
Still, it doesn’t sound good.
Speaking of mice, my husband took his Audi in because the windshield washer did not work.
They found a mouse nest, in a fairly inaccessible spot, where the cords had been gnawed on. Cost over $1400 to fix it. (Insurance covered it.) Since then we have set out traps in the garage, 5 mice already caught. He doesn’t drive as often as I do, so the car sits there inviting visitors.
I’m surprised the check engine light has not come on.
If you have time, there are OBD scanner phone apps ($5-$20) now that will let you see time data from the engine as it’s running and get an idea of what is working/not working.
You will need an OBD scanner device ($10-20) to use these apps. These are Bluetooth/Wifi devices which you plug into the car’s OBD part and use with the phone app.
The mileage is definitely a problem with the air/fuel mix ratio being too fuel rich. There are so many inputs that go into computing the ratio – rpm sensor, air flow sensor, O2 sensor…hard to say which one is malfunctioning. But with 100K+ miles, the alternator is past the prime of its life so it could be a general power issue too.
It’s a good rathole if you have the time to indulge in exploring it. The investment in learning and doing this is mostly useful just for that one time in your life. Only worth it if you enjoy learning about new stuff just for the heck of it.
Ding! Ding! Ding! We have a winnah! Duke University has an Office of Obscure Solutions that should have various forms of exorcists. Hit them up and they’ll relieve your vehicle of any and all gremlins, spirits, demons, etc.
cough up about 22K for a new Ford Maverick mini pick up hybrid…
40mpg.. if you order now you will get it next year…..
they are selling like hotcakes…
Bard the Grim
Yes to 11, 18, and 29. You almost certainly have a bad sensor (or two or three) somewhere that’s messing up the engine operating map with bad input data. Fixing the speedometer problem is probably the place to start. But it’s really weird that none of the mechanics have found (or even looked for?) an indicator in the OBD codes.
And good for you on the stick–Save the Manuals!
My problem solving shade-tree would go something like this: Check for alternator output at reliable 12.7 to 14 volts DC, at the battery, engine running at idle. Buy an inexpensive multimeter, or AutoZone for a freebie–and they would also check battery load capability for a dud bat’ry. A lot of odd gremlins show up when the electricity gets sketchy, and at 100K on an OE battery? Why, sure, pretty good place to start looking. Also, in the same vein, check grounds between the engine and the body and that the connections to the battery are clean and tight at the battery end and at the body/starter end. Stay away from replacing any emissions control or fuel regulating electronics absent a check engine light or using a code scanner, which is another AutoZone freebie. Good luck!
My thoughts are to go out and buy a Toyota.
This has some of the symptoms (if this is a hybrid):
My guess is 1 & 3 are related.
2 is a separate problem. The fix is up thread in the link to the car forum.
With something like this remember to make a car go: Fuel, Fire & Air
It doesn’t sound like a ‘Fire’ problem (spark plugs/wires).
That leaves Fuel & Air. The problem sounds like the car is starving for one or the other or both.
Just because the dealership replaced the manifold air pressure sensor doesn’t mean the 2nd one can’t go bad. That is very unlikely but not impossible.
My gut tells me it is starving for fuel. So check fuel filter, pump & lines.
Do you smell gas when it stalls?
Does it immediately die when it stalls or does it chug a bit and then stall?
@catmandid: That was my favorite episode of Car Talk: The guy describing the noise his starter made as “Haugh-haugh-haugh! Haugh-haugh-haugh!”…and Tommy immediately shouts “Your car is possessed by Maurice Chevalier!”
@pat: I’ve twice found mice nesting under the seat of my motorcycle. They chewed 99% of the way through a very crucial wire. The final 1% gave out when I was 20 miles deep in the woods, not alone, fortunately. Only cost me a bit of solder and some time to fix it, luckily, and a trailer rental.
@Just Some Fuckhead: Yes…same here…my 1999 subaru was doing that (could hardly make it up a hill). Wasn’t diagnosed properly until my transmission guy noted by chance that the catalytic converter was heating up to cherry red and melting the sensor plug on the side of the transmission. Had to replace both CatConvs and that remedied the problem. Ran just fine after that. Old cars tend to have difficult to diagnose problems – the code reader was NO help whatsoever
Yeah, pull codes then go to the interwebs and find what the hive mind have to say.
It’s not a car I’d want to toss money at at that mileage.
@JustRuss: Once came back from a weeklong backpack to find mice had taken residence in my buddy’s trunk, using my trailhead towel for nesting material. Not nearly as traumatic as discovering marmots have eaten your radiator hoses and plug wires (which can be a thing at popular trailheads like Whitney Portal).
I had a similar problem on a much older car, so this may not be relevant. After getting some sort of switch and the fuel pump replaced and the problem still happening, I finally got a good mechanic, who replaced the fuse (engine fuse?). He told me anytime you have an intermittent problem to check your fuses first.
@lee: immediate and sudden stall…. let me figure out the smell.
I have a 6 yr old car with just over 15,000 miles, and yes that’s fifteen thousand, NOT one hundred and fifty. First for half it’s life I walked to work – one mile. Second I had a second vehicle early on that got 50mpg so drove that to work. I had to get a battery last year. Cars now draw current even when off. So a battery is going to discharge even if you don’t drive the car and even as batteries are made better these days they still lose their ability to work properly.
@catothedog: I recall hearing once from a mechanic who was doing a car inspection that there are OBD problem indications that don’t rise to the level of giving you a check engine light.
@Jerry: Ditto spark plugs, bad wiring, bad distributor cap, in that vein.
@David Anderson: Yeah I know that is a weird question but I had an old Ford Pinto (yes one of those) that had a similar problem. It was leaking gas from the fuel pump/line/something (I was 15 my Dad fixed it). So once the pressure dropped at a stop then no more gas to engine.
I’m still leaning towards a fuel problem but a couple of others have mentioned a bad catalytic converter that causes a ruckus. That might be another avenue of investigation.
I would say you have a major vacuum leak someplace. When you brought it to the dealer they must have moved something that stopped the leak temporarily. Over time what ever moved again and its leaking. A good mechanic should be able to check the intake vacuum and track this down.
I drove a 2004 Nissan Quest for 12 years and about 200k miles with that same problem. The charge would last about 24-36 hours if we didn’t drive it. Batteries themselves would last maybe a year before they died.
I got a Die Hard battery with a great warranty. Just swapped out to a new one everyone time one died.
@dave319: I’m also thinking electrical. Symptom #2 and the car initially doing well after the dealer fix, but then got worse again. Wiggle all the connectors.
I like the catalytic converter and the vacuum leak suggestions.
Get a can of starter fluid. With the engine running, trace the vacuum lines to brake master cylinder and anywhere else they might go. If the engine reacts, you found your leak.
It would be a good idea to do a tailpipe emissions check to confirm before replacing the converter.
Hope this helps.
@TEL: It does sound like a failing fuse, or possibly a sensor. Definitely *ought* to be electrical. Presumably they checked the battery leads and the spark plugs. If the wires were failing you’d probably have greater problems at higher speeds/higher loads rather than in first gear. It’s conceivable too that it’s a bad ignition coil, but that typically leads to misfiring. Barely possible that your alternator is not charging the battery well enough…or that you have a poor belt on the alternator.
If the problem were in the fuel supply, like a clogged fuel filter, then (a) it should not reduce mpg like that, and (b) the temporary fix should not have improved things. Likewise, I’d be surprised if a faulty fuel pump would lead to lower mpg.
The air supply seems more likely than fuel, because it would cut into mpg. But they must have checked the air filter first, right? It is somewhat reminiscent of the problems created in days gone by with malfunctioning chokes.
The exhaust system shouldn’t be the problem because your issues are lessened or go away in higher gears. If it were the cat, then the temporary fix should not have achieved much change.
J R in WV
My last Chevy was a green 1971 CustonDelux pickup truck, which cost me $900. I wound up putting in a new starter laying on the ground/ice in February after it wouldn’t even spin over — only good thing was I was parked right beside a rebuild shop, AND they were willing to lend me the necessary wrenches to do the job.
I was a colege studunt also too, this was in the early 1980s. ;~)
Now I am retired, and try not to work on trucks any more. I want a new one, but can’t really load one up any more, so not gonna happen. Best wishes on your car, tho !!!
@SteveinPHX: Owner forums are a good bet and also sometimes a google search. Weird problems tend to repeat themselves.
@MFA: Could there be a ground problem maybe?
I had a mid ’90s Olds that would run rough from time to time. When it did, it had issues with the taillights staying on.
I finally figured out it was a problem with a stupidly placed ground. Why would you put the main body ground in the wheel well GM?
Death Panel Truck
My favorite episode was when a guy called in to say he’d had frost on his windshield and didn’t have a ice scraper, so he used a broken Mountain Dew bottle instead. Later he discovered the bottle had left scratches on his windshield. He asked if there was any way to remove the scratches, and the guys said no, you shouldn’t have used a bottle, you need a new windshield. They were very polite about it. The guy said thanks, and hung up.
A few seconds went by, and then Tom shouted, “WHAT A KNUCKLEHEAD!”
Greg took my first answer: vacuum leak.
However, having worked on cars for a few years, I learned to never make assumptions – especially a “single cause” assumption, based on a previous car’s issue. Also, both time and mileage have their respective effect on various parts.
Good luck and here’s to a reasonably priced solution. Perhaps it’s just a banana in the tailpipe.
@dave319: Late to the thread, I know. I second the low voltage premise. I had one of those 2012 Ford Fiestas that constantly tried to kill me. I began to notice that whenever things were acting up, it seemed more related to the computerized systems giving bad directions as opposed to anything actually physically wrong with the vehicle and that these episodes would be when the car had a hard time starting or the headlights seemed dimmer.
@J R in WV: When I was in college I changed the starter for a friend of my mom’s. A slant-6 Dodge. Just about the easiest job I’ve ever done. Open the hood and it’s right there! Took maybe 15 minutes.
A friend’s father’s 1970 428 Cobra Jet Mustang had a hard life working on a farm. That was a fun car to start, especially when the engine stopped at an orientation where the ground-down flywheel teeth wouldn’t engage with the starter motor. Sometimes a few dozen cycles of bumping the starter switch would finally get it to engage. Sometimes not. :-/ Fixing that required dropping the transmission and replacing the flywheel, from underneath. Not fun at all, and not a 15 minute job!
Ah, the good old days, amirite??
“Grandpa, what’s a starter motor??”