I have a serious problem with my beauty. I have to begin with that the odometer shows 180K Kms, so the engine had its golden years some time ago. I have been fighting the CEL problem for about 7 months now, and can't get rid of it (the code points to the front O2 sensor [bank one], yet the new sensor didn't help).

But lately I have this weird issue, where the RPMs on idle go between 400 and 1000 (most of the times), or they jump to 2000 and stay for app. 5-10 seconds. When driving and trying to accelerate, the engine hesitates and suddenly catches the RPMs in the upper 2000, giving it a sharp push. It seems to be OK when I fully open the throtle. So when the RPMs are between 1500 and 3000 it behaves like stop and go. Sometimes even when you push the gas pedal to maximum (at gear 2 and 3) it does not accelerate at all, and I have to reduce the gear.

I would appreciate any comments.

I have a serious problem with my beauty. I have to begin with that the odometer shows 180K Kms, so the engine had its golden years some time ago. I have been fighting the CEL problem for about 7 months now, and can't get rid of it (the code points to the front O2 sensor [bank one], yet the new sensor didn't help).

But lately I have this weird issue, where the RPMs on idle go between 400 and 1000 (most of the times), or they jump to 2000 and stay for app. 5-10 seconds. When driving and trying to accelerate, the engine hesitates and suddenly catches the RPMs in the upper 2000, giving it a sharp push. It seems to be OK when I fully open the throtle. So when the RPMs are between 1500 and 3000 it behaves like stop and go. Sometimes even when you push the gas pedal to maximum (at gear 2 and 3) it does not accelerate at all, and I have to reduce the gear.

I would appreciate any comments.

 

Wow! I hope someone chimes in on this. I got nothing solid - but I THINK the ECU compares the front O2 to the post cat O2 but how it decides one versus the other I'm not sure - so perhaps the cat is bad or the rear O2 is bad and the ECU is mis-reporting/fooled. I would expect the fron one to go bad first. Do you know the history of this car? Has it ever run rich for extended period? Already had any sensors replaced? Any recent work done? Any signs of rust/corrosion in the engine bay? Any weird dimming of lights? How have you been reading and clearing the O2 code? A clogged cat can rob power but I've never read of one surging like you explain. If you're not getting any cylinder misfire codes, it would seem to be a fuel/air issue or a sensor intermittent - not high voltage related.. Maybe TPS, MAF - I got nothing but guesses.

 

Carl

Have you checked the connection to the O2 sensor clear back to the ECU. There may be a wiring problem.

 

I would check the connections to the MAF and TPS for the engine RPM problem.

Wow! I hope someone chimes in on this. I got nothing solid - but I THINK the ECU compares the front O2 to the post cat O2 but how it decides one versus the other I'm not sure - so perhaps the cat is bad or the rear O2 is bad and the ECU is mis-reporting/fooled. I would expect the fron one to go bad first. Do you know the history of this car? Has it ever run rich for extended period? Already had any sensors replaced? Any recent work done? Any signs of rust/corrosion in the engine bay? Any weird dimming of lights? How have you been reading and clearing the O2 code? A clogged cat can rob power but I've never read of one surging like you explain. If you're not getting any cylinder misfire codes, it would seem to be a fuel/air issue or a sensor intermittent - not high voltage related.. Maybe TPS, MAF - I got nothing but guesses.

 

Carl

 

Thank you for your post Carl.

Here are some of my answers:

I got this car a year ago (with 145K Kms), so I have no history of previous problems (maybe now I do a little). I have been driving with the CEL light on for about 6 months now. I replaced only the front O2 sensor. I forgot to add that driver's side head gasket leaks the coolant (just a bit, but noticable).

To read and clear the codes I go to my mechanic, and he is using the Snap-on tool I believe. The code (I can't remember the exact code reading but it says something like "...one, bank one"). He says it points to the head that is not leaking, so the leak might be irrelevant in this case. I am not getting any cylinder misfire codes.

So you think replacing the rear O2 sensor might help?

I left the car with my mechanic today, and let him take care of it.

 

Cougar - thank you for your comments. I believe the wiring to the ECU has been verified.

 

Much appreciated.

R.

It would be good to know exactly what code is being set. I can't see how changing the rear sensor is going to effect the front one. I would check the voltage from the O2 sensor at the ECU to make sure it is ok.

Just to let everybody know, the problem is a faulty O2 sensor (front one), that my mechanic got from the dealership. Hard to believe, but it's been 7 months since I got this changed, so the dealer won't even exchenge it.

Oh well, at least the problem is solved.

Thank you everybody for your posts.

R.

Thanks for the feedback.

The code (I can't remember the exact code reading but it says something like "...one, bank one"). He says it points to the head that is not leaking, so the leak might be irrelevant in this case.

 

I'm glad you got it fixed. However, you mechanic is incorrect on the leak issue. First, 4-cylinder has only bank one sensors. Bank one does not point to any heads but to the engine as a whole. Silicates present in antifreeze are very toxic to O2 sensors, that explains why it died in only several months. Get oil tested for water, sodium, and glycol for confirmation.

I'm glad you got it fixed. However, you mechanic is incorrect on the leak issue. First, 4-cylinder has only bank one sensors. Bank one does not point to any heads but to the engine as a whole. Silicates present in antifreeze are very toxic to O2 sensors, that explains why it died in only several months. Get oil tested for water, sodium, and glycol for confirmation.

 

Thank you very much for your valuable comment, Jacek. I will pass that info along.