Rough idle, bogs down and shuts off

There could be a couple things that cause this. The fact that the engine runs normally when it starts shows that it is functionally okay. The fact that this starts after it starts to warm up means we are most likely dealing with a sensor or PCM issue.

I am attaching a quick description of the run modes open and closed loop. Basically we want to find out which of the two sensors could be the issue.

If you have a scan tool that can monitor the o2 sensor data, that would be great. If not I would suggest unplugging the o2 sensors and then start the engine when it is cold and see if it continues to do this.

Basically the PCM will run off a calculated program like it does in open loop if it can't read the o2 sensors.

This means it will continue to run off this program even after it is warm which means it will not do this if the o2 sensors are the issue.

If this is not it then we will have to move through some of the items in this guide:

https://www.2carpros.com/articles/symptoms-of-low-engine-power

If it does not do it then we will need to figure out which sensor is the issue. We can test them using this guide or even just replace them.

https://www.2carpros.com/articles/how-to-test-an-oxygen-sensor-02-sensor

However, let's do this first and go from there.

Thanks

Interesting info about the O2 sensors. I received an error code a few days before all of this happened. See attached.

Awesome. That is exactly what we want to see. Looks like you have an o2 sensor issue.

I am attaching the testing for these codes but they are basically the same thing.

However, take a look at the code descriptions at the top of each. Basically they are telling you the same thing as I stated above that they are ignoring the o2 sensor data until it goes to closed loop. So if the o2 sensor is giving faulty or incorrect info then the engine is going to be adjusting on incorrect info and it will run poorly or stall all together.

Run through this info and let us know what questions you have.

Thanks

Okay. I replaced both O2 Sensors. Upon completion, I took it out for a test drive. When I stand on the accelerator, after I get to about 45 mph, I lose power, the “Reduced Engine power “ light comes on and it throws a “cooling fan” error code. The cooling fan was replaced 2,000 miles ago.

I clear the codes, accelerator hard again and the same thing happens - right around the same RPMs.

If I drive it at normal acceleration, like on a highway entrance ramp, no issues at all. No power reduction, no error codes.

It was suggested to me it could be the throttle sensor in the accelerator pedal. What do you think of that?

Thanks.

That could be a sensor but it would most likely not throw a fan code.

So that means we need to find out what the actual code is. Basically if the engine is de-rating and setting this code then the PCM is seeing an issue with the fan and shutting the engine down.

If the fan is not on when it should be and you are at wide open throttle then the engine can overheat. So to prevent that it shuts down.

Also, if it doesn't do when accelerating normally then the position sensor is most likely fine.

What was the code and we can figure out what is going on.

Thanks

Here is the code it is throwing.

Okay. That is great. We are going to have to run through the testing for this code as I suspect this is possible the cause of the whole issue.

Basically the PCM is commanding the fan to spin faster and when it does not then it sets this code and puts on the reduced engine power light.

Take a look at the first page below and it shows action taken.

Please let us know what questions you have working through this and let me know what you find.

Thanks

Thanks. I don’t have much ability to do much testing.

It hasn’t been much of a problem lately, so I just left it alone.

Recently, I had an occasion to punch it and pass someone at highway speed. The check engine light and the “Reduced Engine power” light came on, but power wasn’t actually reduced. I was able to drive it at highway speed just fine. One thing I found is that the cruise control stopped working. As soon as I turned the engine off and restarted it, the check engine light stayed on but the reduced power light turned off. A scan tool revealed the attached error codes. After erasing the codes, the cruise control now works.

Okay. Yeah, that all points to the fact that we need to confirm what I was stating above and unfortunately doesn't change much.

We are going to have to run through that testing to confirm it but I suspect the PCM is the issue.

The cruise is deactivated when the check engine light comes on just as a precaution so that is normal for it to not work and then it does when the codes are cleared. It will work until the light comes on again.

I understand about the testing but unfortunately I am not able to definitively tell you a part that causes this without that completed. Thanks

I am inclined to ignore it because I think it’s a false error.

What is the danger if it’s not false and I keep ignoring?

This is hard to say for sure because clearly the cooling fan needs to perform properly to keep the engine cool.

However, if this is only happening when you accelerate hard and you can drive in a way to not make it happen and the engine never overheats, then it is fine.

I suspect there is an issue with the fan as it is unlikely to cause an issue like this if the PCM is not seeing an issue or at least thinking there is an issue. So it could be a sensor issue but again, if you can drive it in a way to not make the light to come on and go to reduced power mode then I would not worry about it either.

However, just be prepared that it may get worse and to a point where it does it all the time. If it doesn't do this then it should be fine.

5 months ago I had the fan replaced. Is there a sensor that maybe didn’t get plugged back in?

Oh. That is great info. I suspect the replacement fan has just failed.

This fan is a electro viscus fan. This means the PCM commands the fan on by opening a passage that allows fluid to change from one area to another which engages the clutch.

Take a look at the detail below. It could be an electrical issue like a relay but basically it is only happening when the fan is to come on which means the most likely cause is that fluid inside the clutch is not moving to allow the fan to get to top speed.

If something was left unplugged it would have a circuit code and you don't have that.

If it were me, I would look up the part that was used for the replacement and see if there is a warranty. Normally they have a 12 month warranty on them. So whoever replaced it will diagnose it and if it is the fan then they should replace it free of charge to you.

I attached the process below on how to replace the fan if this is something you are going to do.

Thanks for that info.