Unusual and perhaps completely unreleated update.

Have been driving the 2000 Ford Taurus, with the Duratec for anyone that cares. I had it hooked up to a monitor to diagnose a thermostat issue (its stuck open and needs to be replaced), but I was monitoring the battery voltage, and that car seems to drop voltage from an average 12.7 volts to 11.2 and sometimes into the 10s with absolutely no vibration or change to the idle.

Could it be possible that the drop in voltage is normal and it's the car's inability to bridge the drop in voltage that could be the problem, ie the alternator or some capacitor? Perhaps the alternator is doing a good job of keeping the battery charged, but not a good job and adjusting the power feed to the car as needed?

How would one test that?

 

Ok, exhaust manifolds replaced, along with gaskets and donuts...

I had a problem getting the rear manifold and downpipe to the required torque. For now I can't feel any air leaving the joint so I'll address that another weekend.

My idle is now really rough. I tried to perform an oxygen sensor orientation using my ids, but it fails me about 75% through the test with no explanation!

Does that mean one of my practically brand new sensors is now bad? I have no check engine light. When using the ids, I can monitor the voltages at each of the four oxygen sensors, so they appear to work.

Does anyone know what those two metal pipes that go into each of the exhaust manifolds do? There's one small pipe for each of the two manifolds. None of the manuals address them.

Thanks

 

Swapped out ECUs and the car runs normally again.

By normally, I mean that it still has the dip every 32 seconds.

Looks like the exhaust manifolds (and oxygen sensors) were not at fault.

When the weather gets warmer, I'll begin investigationg line voltages with a multimeter to see what's doing.

 

So I took the car to an independent shop that has no specialized Jaguar equipment.

They told me that the car's idle is set about 50RPM too low, and that by increasing the idle, they were able to make the 32 second stumble go away.

That would seem to keep in line with this thread:

https://www.jaguarforums.com/forum/x...solved-126399/

They recommended that I take it to a Jag specialist to get the idle adaptations reset. Unfortunately thats where I took it to last time and they're the ones who set it too low? I figured they would know what they were doing...

Should I mess with that little 3mm screw in the throttle body...

 

Increasing idle always will make a miss like that go away. If the car is indeed idling too low, then it's because one of the ECU sensors is not reading correctly like the MAF, Air intake temperature sensor, coolant temperature sensor , etc. As far as I know the AJ16 modifies idle based on the input from the sensors.

 

http://www.justanswer.com/jaguar/4d8hx-jaguar-xj6-1997-jag-xj6-when-press-gas-pedal.html

I'm going to try this approach.

There are ways to adjust idle, for sure. The shop, with the PDU that I took for has done it for me on another car.

The IDS I have does not reset idle adaptations, but it will read stepper motor position, so this method makes complete sense to me, in theory.

As you know, I don't have an idle air bypass screw, like you do, but I do have that throttle stop screw that the link refers to.

It doesn't seem to require a PDU to make it work either, it simply uses it to find out what position the idle stepper is in at idle and then directs the change based on that info.

I'll post back and let you know!

 

No difference. I made two 1/4 turns and saw no noticeable difference.

I set it back to where I started.

Looks like I'm heading to a Jag Specialist again. I found a different one. Hopefully will get better results.

No PDU. Is it possible to have this done without one?

 

Sorry nothing seems to be working.

IMO, take it to the guy with the PDU of they are reputable and forget about it. This is typically the point when I step back.

Did you test the coil connectors to see if they where degrading with heat? That's something I would ask them to look at

 

Problem solved... For now.

Base idle was reset using WDS. I was told that the base idle level cannot be set to any specific number, so it is where it is.

Right now it seems the car is idling almost 100RPM higher than before, around 644RPM. I want to double check that though.

The shop also noted that the short term fuel trim was at 24.2. They had no explanation for that other than, perhaps a faulty ECU. It was also reset?

In any case...that's what the results are.

 

Well, AFAIK with the car fully warmed on drive you should not be any higher than 600:

 

Well, today the car is idling at about 620RPM, so I believe there's a learning process going on?

By the way, that idle is while the car is in gear. In Park, it's idling at about 750RPM.

In any case, all stumbling is gone. There is no perceptable dip in idle at any regular interval. The voltmeter seem to hold steady as well.

I will continue to monitor the situation and will report back if anything begins to deteriorate over time, which unfortunately, I suspect to be the case. I don't know why I feel this way, perhaps it was because no smoking gun was found to be the cause.

 

Well, Vee sounds as if progress was made, however my '96 4.0 idles at 600 when in drive and also park. There may be a 20 rpm difference but it is not easily determined. I suppose the ECM is picking up the difference of drive and park and adjusting the idle instantly.

Did you ever replace the EGR? A few months back my idle started going up like that and a new EGR fixed it. No problems after that. Maybe I should say so far, anyway. lol
Cheers, RagJag

 

The EGR was certainly one of the parts that were replaced.

The idle has definitely cured my issue. I think I even remember the Jag mechanic bragging to me on how he managed to eek the idle just to the minimum level, which apparently was too low.

What confuses me is that the new shop I took it to mentioned that there was no way for them to manually determine the idle level. It was just a process of resetting it using the WDS. Perhaps the other shop, which has a PDU, managed to do it.

In any case, the car seems to be happy for now. I will gladly return to this thread if things head south again. The new shop surmised that if the problem returns it would most probably be an issue with the ECU. I have a spare ECU that wouldn't read the O2 sensors properly, so I could probably send that one in for refurbishment if I ever decided to spend the money...either way it's nice to know I have a way to get a refurbished ECU without stranding my ride.

Thanks to all who have helped.

 

Final update:

The problem reappeared, slowly, but definitely. I took it to another Jag shop (how lucky that the DC area happens to have two independent shops specializing in older Jags) and it took them some time, but finally found a leaking intake manifold gasket!

I had it fixed a few months ago and I can definitively say that the case of the 32 second idle dip has been cured. I'm going to pin this one on the intake manifold gasket.

If anyone ever experiences this problem, make sure to order the hose connecting the water rail to the pump, part NBC2273AB. It's tucked right under the manifold and is a quick replacement job. It's a $10 part if ordered in advance. It would be a shame to have that manifold off and not take advantage of replacing this difficult to access hose.