1997 Honda Accord runs good cold

Check your fuel pressure

Check cam and crank sensors for resistance if to high it will do that. However we don't have specs on it so check against new.

This post is almost 10 years old so it is unlikely that they will respond.

However, we can help figure out your issue though. If the vehicle runs great when it is cold, then it most likely has an issue with the air fuel mixture once it is warmed up.

This means we need to start with the o2 sensors as this is what tells the PCM what the mixture is once it is warm. The PCM ignores the o2 data until it is warm.

Do you have a scan tool that we can monitor the o2 sensor data to find out if it is rich or lean?

I am attaching a chart below that will help with this.

Basically, we need to start with this to figure out what the issue may be. I would not suggest just replacing the o2 sensors, but most people do just replace them to try and eliminate them.

Let's start with what the o2 is saying and go from there. Thanks

So, if the o2 sensors are okay, then we need to find out what they are saying. Rich or lean?

Basically, we need to know what direction to go so let me know if you can get voltage readings or short-term fuel trims.

They are going to tell us the same thing but in different readings so whichever you have is fine. That is going to tell us if we have a possible vacuum leak developing or not.

You should be able to monitor them when the engine runs fine and then see what they change to when it runs poorly after it warms up.

Great job with the video. That really helps.

This could be a larger issue because the idle dropping like that and it is rattling which points me to a valve train issue.

If that is the case, then we may have intake valves hanging open which will cause all these issues.

So, let's go that route and prove it out or show that is not the issue.

We do this by finding a vacuum line on the manifold and hook a gauge to it and see what the vacuum is on the engine. If you can get a quick video of this vacuum gauge while it is running like this, then we can determine if this is an issue. Basically, rev it like you did and let it settle back out so we can see what the gauge does.

Thanks

Okay. That info will still help figure this out so you can pick one up from most parts stores for less than $20.00.

However, if you are unplugging the temperature sensor and it gets better then you are forcing it back into open loop which ignores o2 sensor data.

So, if this is the case then what is the o2 sensor data reading on your scan tool?

You replaced the upstream o2 and the downstream o2 reads fine? What exactly are they reading when the engine is running this way? I understand you have an air mixture meter hooked up to the upstream but what is the downstream reading? It should be lean as well. If not, then that could be throwing off the PCM and the PCM is leaning out the mixture when it should not be.

That is great.

You said the TPS is good. How were you checking that?

If you look at that data in the second video, when it is running poorly, the spark advance is negative. This means it is retarding the timing and the TPS is around 33% but your foot is not on the throttle.

Then as soon as you tip into the throttle, the TPS comes back down to normal, and the spark starts to advance like it should.

So, it sounds like it is rattling because the spark is too retarded, and I suspect that is because the TPS is not accurate.

If you can inspect this a little more and see that this is the case that when TPS is around 33% and spark is negative, the engine is rattling, then you tip into the throttle a little bit it should smooth out as soon as TPS comes down to normal and spark goes positive.

Sounds great. Keep us updated on what happens with this.

Thanks for the update.

Just an observation, your rear oxygen sensor B1S2 voltage is indicating a very lean mixture. I also saw that the Fuel Trims are both 0 and the car is staying in Open Loop. Thats a sign the car has no fuel control. The car is not staying in Closed Loop for some reason. The only time it will be reading and acting on sensor data is Closed Loop operation. Take a look and see if the car is getting up to operating temperature. And possibly a fuel pressure test.