Unsolvable Explorer Rough Idle. Any OBD II experts?

[Cashcrazy]

And I just passed on a real clean used SUV hoping to get this resolved. Hope I didn't make a mistake lol

StreetRod- Do you know how to read the O2 data? And wow!! Cats are expensive!

 

[2000StreetRod]

. . . StreetRod- Do you know how to read the O2 data? And wow!! Cats are expensive!

I know about the pre-cat sensors but very little about the post-cat sensors. If the engine is running rich the cats will overheat and rapidly fail. However, I suspect that your LTFTs are keeping the mixture within normal range. The PCM typically has fairly extensive self testing of the cats utilizing the O2 sensors. The shop manual drawings indicate that the cat assembly utilizes two different types of cats instead of a three way cat. The downstream O2 sensors are on each bank between the first type cat and the 2nd type common cat that follows a "Y" after the bank specific cats. In your case, there is no way to test the 2nd type common cat. Do you have annual emissions inspections in Texas?

 

[Cashcrazy]

Luckily no strict emissions in my county.

 

[Cashcrazy]

Anything else come to anyone's mind to test?

 

[gmanpaint]

Have you replaced the ECM temp sensor?

 

[Cashcrazy]

Gmanpaint- By ECM temp sensor donyou mean the coolant temp sensor? If so I monitored that and it looks to be functioning properly.

Is anyone here an expert with reading catalytic converter data?

 

[gmanpaint]

Yes. There are two of them. One for the cluster, one for the ECM. I have had the same issue as you in the past, and turned out to be a $20 ECM temp sensor was giving wrong data, causing the A/F mix to be wrong.
If it runs alright from a cold start, but if you shut it off after warm up, restart, and it runs rough, this sensor is the culprit. If you don't have this issue, nevermind. Just thought to throw something else for you to try, as it seems you have done a lot already, but I didn't see if you replaced this or not.

 

[2000StreetRod]

On my Sport when the Spark Source = 9 (Idle Feedback) the PCM alters the spark advance to partially control the idle speed. The IAC valve is an electro-mechanical device while spark advance is electronic and can change much faster. I suggest that you monitor Spark Source, engine speed and spark advance while the engine is idling. It's possible that Ford decided not to implement spark advance idle speed control on your model since it may result in higher emissions.

 

[Cashcrazy]

I didn't replace this. Where is it located? Are you running a 4.0 SOHC? I just looked at Rockauto and I see the air intake temp sensor and the coolant temp sensor. Is the air intake sensor what you replaced?

 

[Cashcrazy]

StreetRod- any idea what PID monitors spark source?

 

[2000StreetRod]

The engine coolant temperature (ECT) sensor provides temperature data to the PCM. According to the wiring diagrams the engine temperature sender for the instrument cluster was deleted in the 2003 models. The PCM sends the engine temperature to the instrument cluster microprocessor via the SCP data bus. You've already tested the ECT sensor.

 

[2000StreetRod]

For my SCT PowerFlash I use the PID spark source.

 

[Cashcrazy]

You mentioned another guy that had a rough idle that was not solved. Did he replace intake gaskets? My valve covers are getting leaky and it looks like the intake will have to be removed. I'm thinking about hitting that project next weekend to eliminate one more know problem area.

Does anyone have a service manual for a 2003 with this procedure? The torque specs would be helpful.

 

[gmanpaint]

I found a coolant temp switch sensor, AND a coolant temp sensor offered for your engine, on O'reilly's website. Whats the difference between these?

 

[2000StreetRod]

I found a coolant temp switch sensor, AND a coolant temp sensor offered for your engine, on O'reilly's website. Whats the difference between these?

The photo below shows the lower thermostat housing that Rock Auto sells for the 2003 with the SOHC V6.

As you can see there is a plug in the port that used to house the engine temperature sender. You can still buy a sensor and install it in the port but I doubt there is an electrical connector for it in the wiring harness. I actually prefer redundant sensors like the earlier models had. When I installed my aftermarket oil pressure gauge on my Sport I retained the functionality of the oil pressure switch that drives the simulated oil pressure gauge in the instrument cluster which has no more functionality than an idiot light.

 

[Cashcrazy]

Maybe one is the IAT and one for coolant??

I am working on a gasket order and don't want to miss anything. Does the EGR have to be removed on mine with the intake?

Intake orings
Valve cover gaskets
EGR gasket(possibly)
EGR tube oring(possibly)

Am I missing anything? I know the pid data doesn't point to vacuum leak but I'll replace them to eliminate the orings since it's a known problem

 

[2000StreetRod]

When the PCM is in closed loop it continuously cycles the fuel mixture between slightly rich and slightly lean to reduce emissions. The change in fuel mixture will affect the engine speed unless the spark advance and the IAC valve compensate to minimize the variation. As I recall, there is about 1.5 seconds between successive slightly rich peaks. I don't know if the PCM anticipates the engine speed change or if it just reacts to the detected change. I suspect the latter which means the IAC valve and the spark advance will always be "chasing" the desired engine speed. The 2004 and later models have electronic throttle control with no IAC valve. I think a stepper motor is utilized to control the throttle plate opening and the idle (or any other engine) speed. It may be more responsive than the IAC valve but I prefer the simplicity and reliability of a cable with return spring controlled throttle plate. A failed open IAC valve cannot allow the flow of nearly as much air as a failed open throttle plate.

 

[2000StreetRod]

According to the shop manual drawing the EGR valve is attached to the throttle body. The intake manifold is removed with the throttle body attached so it is only necessary to disconnect the EGR tube from the EGR valve. In that case no EGR valve gasket is required. I see no EGR tube O ring. It should just be a pressure fit since it is high temperature.

I think since 2000 the IAT sensor is integrated into the MAF sensor for the 2nd and 3rd generation models.

 

[Cashcrazy]

I read in my chiltons manual that the MAF and IAT can not be replaced separately. I guess they are also saying it's one part. I'll go ahead and get the EGR gasket so I can seperate and clean it out. Just about have my order ready.

Also, I will start spraying that EGR tube daily with WD40 since I can't replace the gaskets until next weekend. Hopefully that will loosen it up.

 

[2000StreetRod]

Below is a photo of my old, stock 55 mm MAF sensor.

As I recall the vertical wire with the little blob outside and parallel to the cylinder is the IAT sensor. I suspect the little blob is a thermistor. The MAF sensor element is suspended within the cutout section of the cylinder.