Error Codes 0171, 0300, 0302, 0441 - 2000 Corolla

[Timbo66]

Please help! I know a lot of other poeple on this forum have posted similar problems, but I have yet to find a clear resolution.

Here's the deal; 2000 Corolla with AT and130,000mi
I have researched and understand the ODB codes listed in the title, and what the 'possible' solutions are, but with these combinations of errors, I'm trying to narrow down the possibilities before throwing money at the car.

Here's what's been done already; New NGK plugs, vaccuum leak test on the intake system, dealer says O2 sensors are okay (although I wonder). New MAF too. After they did this work, the errors came back within a week. I have done fairly in-depth work on cars in the past, and plan to try to fix these problems too.

The 0441 code is new, but the others have been around for a couple of months.

Symptoms;
Rough idle on start-up, once warm it is much better, but still a short (1-2 second) delay on acceleration from a stop. No complete stalls. Highway driving is usually pretty good. Every once in a while if I 'hit it' on the highway, I get a 'lurching' sensation in the engine. Also, sometimes if I am going about 45, and 'hit it', the car doesn't want to down shift to get the proper acceleration and it feels like it is bogging down (almost like timing issue). Also, I am only getting about 31 mpg-mostly highways (seems low).

I have my guesses at what to do, but I am hoping to hear your guys' thoughts.
Questions?

Thanks again!

[fishexpo101]

First - reads all the codes that are stored and reset the ECM. Have to see if the EVAP code (P0441) comes back or not - hoping not, as that complicates some matters.

Average fuel economy of 31MPG is not bad - depends on the transaxle - if it is a 3-speed, that is pretty good. If you have a 4-speed - that is about ballpark to a hair low for typical, steady state driving. Now if you have been averaging significantly more before, example you used to average 35MPG+ for the same kind of driving, then I would consider that a problem area.

The P0171, P0300, and P0302 along with poor drivability and possibly reduced fuel economy points to a fuel or fire problem.

P0300 points to a random misfire condition, P0302 points to the #2 cylinder/plug/coil being the problem. I'd start by swapping the #2 coil pack with #3 coil - basically swap the two middle coil packs. Reset the code and see if it follows the coil or stays with the cylinder.

P0171 points to a lean fuel condition - this pretty much can mean anything right now. Could be a MAF sensor, could be an exhaust leak close to the O2 sensor (the donut gasket between the exhaust manifold and downpipe, is a problem area for many cars). Could also be a bad O2 sensor, bad or clogged injectors, bad fuel pump, clogged fuel pump/regulator/fuel filter (all of them in the gas tank), could be bad tank of gas, could be a faulty or confused ECM, clogged induction system (gummed up or dirty throttle body, clogged air filter, damaged airbox and associated tubing), heavy deposits on the intake side of the head (could be on the valve), etc.

Given the age and mileage of the car - I'd say you stand a good chance that replacing the primary O2 sensor (upstream one, before the catalytic converter) is a good maintenance call at this point. I'd recommend sticking with Denso OEM sensors - you can get them online for considerably less than what the dealership would charge you. I'm at 153K miles on my OEM Denso sensor - and average better than 36MPG on my 4-speed 2002 Corolla. Some have seen their sensors give out sooner than 50K miles. Sensor can be bad and not trip a CEL - only way to test for sure is to back probe the sensor or at least data log the sensor during operation.

If you haven't done a comprehensive tune up on the car yet (you already got the plugs, and checked for leaks) - go ahead and do so. That will eliminate a good number of "potential" issues and give you fresh plate to work on. Check to make sure you have good spark. Check to make sure you have good injection. This means wiring in NOID lights or listening to the injectors "tick", injectors may have to be pulled to be flow tested, checking fuel pressure at idle and at speed (little tough to do without the right equipment), data logging to look at fuel trims and other sensor outputs seeing exactly what the engine is trying to do.

[Timbo66]

fishexpo101-
Thanks for the thorough reply!

I like the idea of switching the coils to see if it makes an impact.
Then, I was planning on changing the O2 sensor.

I've heard this generation of Corollas burn some oil. From your experience, how much is 'normal' for these cars?

[fishexpo101]

Ideally, no oil should be visibly consumed between oil changes - but in the end, all engines will consume some oil. Normal generally runs in the couple of ounces to 1/2 quart every oil change. If the engine has a lot of miles on there - I might let it slip to a quart every oil change. To give you one set of data points - my 2002 Corolla and 2003 Matrix - run synthetic motor oil exclusively, and oil change intervals between 5K and 8K miles (no more than 10K-12K max for me) on OEM or better "tall" oil filters - I don't visually see any oil consumption. I know it burns some, all engines do, just that it replaced what it burned off with fuel (fuel dilution in the oil) - which is normal.

When you should be worried about is when it starts to become excessive - depends on your source. Toyota says that consumtion exceeding a quart every 700 miles is excessive. That means in a typical, short oil change interval of 3000 miles - you'll have to add over 4 quarts of oil! In my book - anything over a quart every 3000 miles is excessive - will only get worse from there.