This time I need help. My daughter is away at college with her 94 Camry with the 2.2 5S-FE engine. She said for several weeks the car was starting hard then in the past week the car was idling rough and wanted to die at stop lights. When at speed the car ran great. So... I was thinking EGR or IAC valve. Today the check engine light finally came on so I had her read the codes. She's getting code 25, air fuel ratio lean and code 26, air fuel ratio rich. Not what I expected.

The good book points at an O2 sensor, injectors, coolant temp sensor, air intake system, etc. Just like everybody else, I'm looking to save a buck and in my case, time. Has anyone had experience with either of these codes and/or symptoms? I'm trying to come up with a good plan of attack. I appreciate any input.

I would start with looking at O2 sensor: the car is 13 years old.

She may be able to unplug the O2 connector (of course if she can find it), start the car and then read the codes again with the sensor unpluged. See if she will get different codes now.

Good luck,

Sam

Agreed. Found a post on another forum that says if you have both a code 25 & 26, the O2 sensor is bad. Plus after reading a little closer in a Haynes manual it says if you get code 21, 25,or 26 disconnect the PCV valve and measure the sensor voltage at the test plug. If you see 0 volts, replace the O2 sensor.

Some say you should change O2 sensors every 50 - 100K miles as scheduled maintenance. Even if this doesn't fix her problem, it's "that time" anyway. I'm going for the main O2 sensor to start with. Thanks for the help.

It's tough to say which one it maybe. Could be both. They seem to usually go at just about the same time. Although pricey I'd do both to be safe.

I'll try the main first and see what happens. Just want it fixed for now. My duaghter will be doing the work. If that fixes the rough idle and codes, I'll go ahead and change the other sensor next time she gets the car home from college. If the main sensor doesn't fix it, I'll have her take it somewhere to change the sub sensor (downstream). I don't want her crawling under the car. Thanks for the suggestion.

RIP,

"If the main sensor doesn't fix it, I'll have her take it somewhere to change the sub sensor (downstream). I don't want her crawling under the car".

Just an FYI. On the 94 4 cylinder 5SFE engine both O2 sensors are easily accessible from the top. She can just unbolt the top one by removing 2 nuts (old Toyota style), but will need an O2 sensor socket for the bottom one. It's the generation 4 5SFE engine where the O2 sensor past the converter is only accessible from underneath the car.

Mike

Yup, and if I had looked at the factory manual "sticky" like I preach, I would have known that. Sometimes the brain grinds it's gears. Thanks for the info. I may need it.

Daughter changed the main O2 sensor. Check Engine Light stayed off for two days then returned. Now getting just code 25 - air/fuel mixture lean. Original rough idle problem never wet away. Taking a trip to look at the car. Will let you know.

Fixed! Found the "smokin gun" too.

Took a trip and got my hands on the car. Found it not only had a very rough idle but also an intermittent miss/surge at speed. Checked the codes again and found code 25 (air/fuel mixture lean) still there and code 26 (air/fuel mixture rich) had returned. Started with the basics and lucked out...

Stuck a timing light on all plug wires and got constant strobe on all. Wires/cap/rotor/coil/ignitor good. Decided to pull the plugs for a look see. Went to pull the wire off plug #2 and it came right out without the extender. Fished the extender out and found a hole blasted through about midway. Apparently, the wire wasn't correctly crimped to the plug contact inside the extender, arced it's way through it, and intermittently arced to the wall of the plug wire well in the valve cover.

Changed the plugs and plug wires and all was well. Did I change the O2 sensor in vain? Well...like many do, I'm sensing the car is running better than it has in years and to some folks trains of thought, O2 sensors should be changed periodically anyway. In a way I was disappointed. I was loaded for bear with test equipment, tools, chemicals, and a stack of written material. Only used a tad bit of it. I'm just glad this headache is over. Cheers.

Thanks for posting the final fix. Sometimes on today's modern engines when we trace down a problem, we forget the basics; these are still internal combustion engines. Sometimes I long for the days of points and a condensor. I think I still have my tack/dwell meter, just in case they ever come back.

Anyway, glad your daughter's problem is finally fixed. Did you get new OEM Toyota plug wires or go with the aftermarket ones?

Take care.

Mike

Used Bosch wires. Don't recall the brand that was in it but, remember I paid about $30 for them a bit over a year ago. Payed $50 for the new Bosch wires at an Autozone. Hoping the higher price means higher quality. Unfortunately, that's not always the case.

Ya. Getting to the point where you need a PHD in Astrophysics anymore to work on these things. Sure wish I had my old Cougar back. Thing was a piece a cake to fix. Cheers!