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So, I have a 2007 Corolla [about 90,000 miles] that idles rough (rougher when I use the power windows or the AC) and was throwing a 0420 code. Here’s what’s happened up to this point:
1. For the first five years I owned it, it ran fine and I didn’t have a single problem. Then it started accelerating sludgily, using gas faster than normal, idling rough and the 0420 code came up.
2. I took it to my [trusted] mechanic [Mechanic 1]. They referred me to a shop that specializes in catalytic converters [Mechanic 2] and the like, for the 0420 code, and referred me to the dealership for the idle problem. Mechanic 1 said that the dealership has more experience with my specific car.
3. I have gone back and forth between the dealership and Mechanic 2 about ten times total. They cannot seem to figure the thing out.
4. In trying to address the rough idle and sludgy acceleration, the dealership replaced the air fuel sensor and a seal on the mass air flow sensor. They held on to my car for three days total. (I got sleazy vibes from these guys.)
5. Mechanic 2 replaced the catalytic convertor twice (something about a hole in the first replacement), both O2 sensors, the spark plugs, the PCV valve and put some kind of cleaners through the fuel system. They seemed to be running all kinds of tests, doing research (I sat at the shop, for part of a day, and watched as a mechanic moved back and forth between my car, some devices and a computer, in an increasingly harried manner) and working with someone outside of the shop called the “tech team.” They had it about a week total. (I got good vibes from these guys.)
6. I’ve cleaned the mass air flow sensor with electronics cleaner, replaced the engine filter and also replaced the battery (it was close to dying).
7. I’ve dropped $1,800+ on these problems (which is a lot for me).
8. The sludgy acceleration has mostly gone away (it still seems to be there a little bit at slower speeds, but that might just be me being oversensitive), but the rough idle is still present. Also, both my Mechanic 1 and 2 said that, although troubled, my car is okay to drive. Mechanic 1 suggested that until the problem gets a little worse, it’s a guessing game.
9. On a Toyota forum, it was recommended that I replace the intake gasket, clean the throttle body, test the fuel pressure, look at the spark plugs and test the cylinder compression. But aren’t these things the dealership or Mechanic 2 would have already done? (I decided to post here, because Eric the Car Guy explicitly recommended against taking out the throttle body, which was recommended to me on the Toyota forum, so I though I might get some more sage advice here.)
What do I do? Is this a difficult problem to pinpoint or are the mechanics taking shortcuts, or neither or both? Should I be driving my car? Could I burn through another catalytic converter? Is this just what cars at like as they get older? Am I overreacting? Are all these problems related?
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Wow… or Golly….
This is a nice one to step into…
I will throw some spitballs out, because not having the car in front of me and having it been through two techs (including the dealership) and not getting it fixed can be challenging…
For one. I will just go stream of thought…
You had a P0420 code at “relatively” low mileage… While earlier Corollas suffered through this when the Cats were still good (and would fail emissions, even though they could pass tailpipe standards), by your year they had re-flashed the PCM’s and they were more accurate and not going off when the cat was still working well…
A P0420 as you know is a catalyst inefficiency code… Meaning generally the cat has gone bad… So many times the downstream O2 is thrown under the bus, and is a wasted $75-$150 from where you got it….
Also Toyotas are real picky about O2 sensors they only like Denso’s…. Do not use Bosch, you can have issues like this…
Going back to the P0420 leads me to believe there was failure in the cat for some reason… Oftentimes it is due oil contamination, engine misfires, or an improper fuel/air mixture getting by that burns them up and make them go bad this early…
What leads me to think that I would check for an exhaust restriction somewhere… Perhaps not the cat, but further back (pipes or muffler)… This can be tested using a backpressure tester in an O2 bung, but is tested much easier with a vacuum guage, Eric has a great video on how to use this to diagnose an exhaust blockage…. A blockage would cause poor fuel economy and rough running… and may get glossed over… Why there would be a restriction? I cannot say…
Fuel pressure should have been tested somewhere along the way… I believe a Corolla should be around 50 PSI… While Toyotas are known for very robust fuel pumps, there can be a fuel delivery issue somewhere… There is a filter on the fuel pump, and while these are supposed to be “lifetime” they can go bad… Also fuel restriction (pinched line) delivering pressure but not volume… An inspection under the vehicle of fuel lines should be done…. A true test involves timing and measuring the volume of fuel delivered and is very rarely done… These are remote, but possibilities.
The recommendations from #9 on your post are not bad… but I would do them in reverse order from what you have listed… I would start with looking at the plugs (use NGK’s), checking the compression, then testing the fuel pressure… Intake gaskets problems should manifest themselves with high O2 readings in the O2 sensor and generally set a P0171 code (lean condition)… Fuel trims should be observed as well as upstream O2 sensor readings switching back and forth properly from lean to rich by a scan tool…
I hope I don’t confuse more that help… These are just some things to throw out for the gray matter…
Good luck and let me know if you need any more clarification…
Cheers
-Karl
I really appreciate your response. Thank you.
The catalytic code has not come back up (for now). But I’ll look into diagnosing the blockage.
I’ll start on the #9 recommendations the best I can. I’m new to working on my car, like just-learned-how-to-change-the-oil new, but checking the spark plugs looks manageable and I can go from there.
Here are some follow-up questions:
A) I have to move in the next couple of days as well as a small a trip planned. In your experience, is it okay to wait a little bit to try to find the source of the rough idle and continue to use my car in the mean time?
B) What do you make of Mechanic 1’s recommendation that continue to drive the car until the problem become more pronounced?
Regarding driving the car until the problem is more pronounced. It depends. What you do not want to do is continue with a problem that may require another catalytic converter replacement $$$.
Did anyone check the functional performance of your upstream O2 sensor, your long term and short term fuel trims at idle and while increasing rpms, and for any misfires(although misfires should throw a check engine light)?
The reason I ask is that these are easy checks and you do not want misfires or too rich a fuel mixture running through your engine. That will cause premature wear of the catalytic converter.
One free and fairly fast way to get these readings is to go to an Autozone and see if they can hook up a scanner to your vehicle and tell you if the upstream O2 sensor is working correctly, whether or not there are any misfires, and if there is anything wrong with your long term and short term fuel trims. (Do not buy anything based on a recommendation from an Autozone employee until you double check the reason for the purchase with an independent third party. These employees are helpful but also in the business of selling parts). Another option, you could also call Mechanic #2 on the telephone and ask him since he replaced the O2 sensors.
If the upstream o2 sensor is working correctly, there are no misfires, and the long term and short term fuel trims are normal there is less risk that you will prematurely wear out your new catalytic converters.
Also, how clean is your air filter? If it is very dirty upon visual inspection stop by Walmart, pick up, and install a new one. A really dirty $15 air filter can cause a rich fuel mix condition and rough idle. Simple, I know.
About your first question, is it OK to wait to find the rough idle issue… That is difficult to say without really seeing and hearing the car and running some checks… some things you can get away with, some things may do damage and make things worse…
Second question… I really don’t like the answer the tech gave you about drive and wait until it gets worse… It means IMHO that he has given up and has no answers… A car as relatively new as yours should not run that bad… Generation 7 and Generation 8 Corollas are still on the road purring like kittens…
-Karl
I’ll add that engine mechanical is often overlooked in these situations. If you have a mechanical issue such as low compression on a cylinder, no amount of sensors you throw at it will solve the problem. When dealing with a ‘mystery’ issue like this I find it useful to rule out mechanical issues first and take things from there. More information you might find useful here.
http://www.ericthecarguy.com/faq/solving-automotive-idle-problems
http://www.ericthecarguy.com/faq/solving-automotive-performance-issues
Keep us posted.
Thank you guys for all your responses. I’ll start trouble shooting after the holiday.
A couple more things, that may or may not be anything: Yesterday and today I’ve noticed that when I start the car after it’s been sitting for a while, it takes a few stops before the idle starts being rough. Also, I’ve noticed that the car will run rough when going in reverse at slow speeds.
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