Noticed for about a week now, the engine sounds like it is working noticeably harder right after the starter turns over, and it stays that way until I put the car in gear. It also sounds like it is working harder when I accelerate in 1st and 2nd gear. Once I get the engine warm and over 30mph or so it is not so noticeable anymore. I've read everything on this, from exhaust leak to timing belt (the timing belt was replaced about 30K ago).

When it starts the engine seems to idle at about 1500-1700, then drop to about 1000 when I put it in gear. I'm not sure but isn't 1500 a bit high for idle?

Anyone had direct experience with this?

98 Camry V6 with 193K

Thank you!

 

Working harder as in idling at a higher RPM?

Is this every time you start the engine or just when it is cold?

 

Well it sounds like it is at a higher RPM, but according to the meter the RPM is normal. The issue is just that the engine is making this different sound, on the cold start and when I accelerate. It does not do it when the car starts warm. Went to Autozone, code PO135 pulled up, which is an 02 sensor malfunction apparently. Not sure how this might be connected.

 

Might make sense.

This code is for the heater circuit for the 02 sensor.

The sensor needs to be hot to work. On older cars without heated 02 sensors the exhaust eventually heated the sensor up to a point it would operate.

The heater gets the 02 sensor hot regardless of engine hot or cold or exhaust gas flow.

Perhaps with the heater circuit failure the sensor now needs time to heat it up. Before this the engine is operating in some kind of fail safe mode.

 

So, the engine is making this louder noise because the 02 sensor circuit is failing? I don't quite understand how the two are related...is this faulty sensor making the engine run in "open loop" all the time, hence sounding different? (No idea what "open loop" means.)

Thanks.

 

Questions:

The engine working harder may be just that the engine sounds louder?

The engine works harder (or the noise) when cold but is OK when trans put into gear?

Works harder cold when in 1st or 2nd?

The RPM versus MPH is not different hot or cold (meaning the engine needs to work harder when cold=more RPM)?

Closed loop. The engine adjusts the air/fuel ratio based on real time inputs from the various sensors, one being the O2 sensor(s).

Open loop. One or more sensors is outputting a signal that does not fall within a defined programmed range for the engine operating conditions. The computer then sets the air/fuel ratio based on a default output signal for the problem sensor. The result is typically a rich fuel ratio.

Typically a failed 02 sensor results in high fuel ratio, decreased MPG, high emissions-failed smog test but the engine otherwise runs OK. Sometimes it can cause very strange operating problems.

It may not be the cause of your problems but its always best to first fix the problems that are obvious, this being any trouble codes. If the 02 sensor heater circuit is bad, the 02 sensor is not working when the engine is cold.

 

Yes, it just sounds louder. At first I thought it was working harder, but the RPMs are normal, so now I'm thinking there is a small hole in the flex pipe making it sound louder.

I hear the louder noise when the engine starts cold AND when I accelerate, in any gear. The only time it sounds normal is when it is warm and I am not accelerating.

I don't understand what you meant by "The RPM versus MPH is not different hot or cold (meaning the engine needs to work harder when cold=more RPM)?"

Thanks for the loop explanations, that makes sense. Car is at shop right now to look for exhaust leaks.

 

my car makes a loud rattling noise, went by dealer and told me that the catalyc converter is lose inside the exhaust.