Hey Guys,

This may or may not be connected to my other thread concerning a code 1316 that my car threw.

Car currently has a lumpy idle that it hasn't had before. Car runs completely normal off idle with plenty of power and smooth response. The symptoms are a little rough idle constantly with a dip in the idle about every 30 seconds or so where the car gets really lumpy and then recovers. No stalling

What I have changed:

1) First thing was replaced all the plugs with OEM versions. No change
2) Disconnected one coil at a time. Each disconnect resulted in a drop of that cylinder but the car would still drop every 30 seconds and recover. So I ruled out the coils as being the source. Each one perfectly replicated.
3) Changed fuel pressure regulator with new one (could smell fuel from the vacuum line and thought for sure this was the issue) no change
4) Removed and cleaned an extremely dirty and gummed up throttle body and IACV. Surely this was the issue - nope the lumpiness actually got worse after that cleaning but I write it up to the ECU needing to relearn the original settings.

Fuel filter was replaced with a new one last year so I don't suspect fuel supply just yet.

Not sure if I should be suspecting a failing TPS now or the CPS?

Any input is appreciated.
It does seem to get worse as the car warms up.

Could an overheating issue have damaged the water temp sensor?
Its been resolved but maybe it hurt the sensor

Cheers
Bernie

 

OK,

Here is a really interesting clue.
I timed the lope and it happens every 32 seconds and I mean every 32 seconds. This lope must be driven by the ECU somehow? Maybe it is reaching out to a sensor and not getting a reply so it lopes and then recovers.

Anyone ever had a problem like this?
Its crazy that I can time it to the second.

Cheers
Bernie

 

Have you tried cleaning out the fuel injectors? its not hard to take them off the port,

 

No,

Haven't done that yet but it is on my list.
Getting them off is no issue but wht do you guys do to clean them? I have sent injectors out before to have them cleaned from other vehicles but have never cleaned them myself.

The car seems to run more smooth when cold and once warmed up gets into that loping every 32 seconds. What has me interested is how consistent the lope is. Seems to me that it is somehow driven by the ECU on the car. If it were an intermittent issue I wouldn't expect that kind of consistency.

Cheers
Bernie

 

I had to laugh this AM as I sat in my driveway and my idle seemed to "drop" for a second....you guessed it, ever 32 seconds! Interested in hearing what resolves this .

 

Hi Bernie,

Below are links to photos showing how I cleaned our injectors at home, based on various methods I found online. I was concerned that just soaking them in cleaner would not be effective enough due to a lack of manipulation of the internal solenoid valves. Even ultrasonic cleaning may be less effective in that regard. I think my total cost was about $50.00, including the new filters and O-rings, a couple of bottles of Techron, the PVC pipe & fittings, the rubber hose and valve, and the Bosch EV-1 connector. The photos are of our '93 XJ40, but its fuel rail, FPR and injectors are virtually identical to an X300:

Welcome to Jag-lovers - Members Photo Viewing Page
Welcome to Jag-lovers - Members Photo Viewing Page


The first thing that comes to my mind is your suspicion of the water temp sensor, or Engine Coolant Temperature Sensor (ECTS). If it has stuck and is telling the Engine Control Module (ECM) that the engine is always cold, the ECM could be continuing to apply cold-start fuel enrichment even after the engine has warmed up. I wonder if 32 seconds is a pre-set time programmed into the ECM to discontinue cold-start enrichment as long as the ECTS signal indicates that the engine has reached a sufficient operating temperature? Is there any indication that your engine is running rich?

Cheers,

Don

 

Thanks Don,

I have been traveling for weeks on business.
Just getting around to this again.

Can't say that the exhaust smells like a rose these days but it could be a little on the rich side of it. However, I just had the car smogged before I left town last and it passed without issues. Not sure how rich the car would run if the problem you are describing existed.

Having said that, I am having temp issues with the car which are driving me bonkers.

Bernie

 

So,

To further the investigation, I have had the fuel injectors cleaned and the lumpy idle is still there.

I think I have covered all fuel related items and I am sure the car is better for it but kind of frustrated that I still haven't found the root cause yet.

There is something else going on that has always been that way which might be a clue or at least something else I need to address.

Most noticeable at highway speeds, when I pull my foot off the throttle the car takes about two seconds before I feel it starting to slow down. A delayed reaction in my pulling my foot off the accelerator. I have read about the throttle cables needing more tension but my throttle snaps completely closed mechanically with no binding whatsoever.

Have also removed and thoroughly cleaned my throttle body so it cannot be the culprit either. Can the ECM send such a delayed message to closing the butterfly? Can the IAC cause this to happen?

I have seen numerous messages from people with similar issues.

 

Hi Bernie,

Sorry to hear you're still having issues.

Off the top of my head, here are some questions that come to mind:

Is the car still triggering the P1316 code, or any other codes?

Have you considered replacing the Engine Coolant Temperature Sensor (ECT or ECTS)? As I mentioned before, if the ECTS begins to malfunction, it can cause the ECM to adjust the air-fuel ratio incorrectly. For example, it can cause the ECM to continue to apply cold-start fuel enrichment even after the engine is warm. It can also affect the adaptive fueling offset and the Idle Air Control Valve stepper motor adjustment because the ECM takes coolant temperature into account in making those adjustments.

You can test the ECT resistance when the engine is cold and hot to see if it seems to be changing properly. For example, at 68F, the resistance should be about 2.5 kohms. At 193F, the resistance should be about 0.25 kohms.

There is a "time to warmup" test mentioned in the EMS manual, in which the ECM checks that the sensor responds to a rise in coolant temperature, and another test that checks for an abnormal fall in coolant temp once the temp rise is confirmed. The manual does not state the consequences if one of these tests fails, but it is possible that it could cause the ECM to go into a default fueling map that ignores coolant temperature.

I can't remember if the TPS has been mentioned, but since its signal is used by the ECM to cut off fueling on overrun, it could be related to your symptom of the rpms not falling as quickly as you expect after lifting off the throttle. You might want to test your TPS for dead spots.

Cheers,

Don

 

So, is the 32 seconds real? How sure are you? The next step would be for set up some form of data capture to see what is triggering the lope. OR, XJR Engineer Andy could ask one of his SW buddies what happens in 32 seconds!

 

Hi Don,

Sorry the replies are far between.
Really a busy person travelling a lot and don't have a lot of time to investigate stuff. I really appreciate the help!

Ok,
So I guess maybe the last time I took it to the shop to have codes checked, they reset the system and now I have not completed a drive cycle properly or the system won't reset for some reason. I have evap and catalyst not ready. Looking for the proper drive cycle information to get that to reset as we have been driving the car for quite a while since it was at the shop and I would have expected it to have set already?

I took a look into the temp sensor today and the results might give us a clue.
I measured the resistance on the sensor cold at it was 1.8 kOhms. Now cold in Vegas is like 85 degrees. With the engine at about 190-ish, the sensor was giving off whacked out resistance readings. First it was just zero's and overloads on my meter. A little while later it was 302 ohms! So are we pretty certain that this sensor is failing under the heat?

I paid attention on startup today and the car really stumbles for 5-10 seconds when first started and it smells rich. After that it settles down but never stops loping every 30 or so seconds. As soon as you put your foot on the gas to move, the car is as smooth as silk.

Not sure if there is an issue with the TPS yet but it did that hang long before I had a lumpy idle so I suspect the two are not related.

B

 

Just confirmed this again.

Car was cold by Vegas standards.
This time I disconnected the sensor and put probes on it so I could monitor a change in behavior as the car warmed up.
So the engine was running the whole time

Started over 1 kOhm

So the Ohmage dropped as the car warmed up.

Engine got to about 190F and the Ohms were in the low .3 kOhm range.

Looked at the temp and then went out to look at the meter and the Ohms had gone to 302 Ohms.

So based on what has been said, this temp sensor is faulting at higher temps.

Gonna order one anyway

B

 

Dude, I went through your exact issue, 32 second dip in idle and all. Do a search on the XJS forum, you'll see everything I went through.

It's your intake manifold gasket. Change it. Drive it for a few days and watch the symptom slowly disappear as the ECU relearns how to operate without that leak throwing things off.

While you're in there, you should replace the water rail hose that is cheap to buy and easy to replace with the intake manifold off.

 

Bernie:
I am not sure I understand exactly what you are measuring but .3KOhm IS 300 Ohms. Are you measuring the sensor without the ECU connected or are you trying to measure resistance in parallel with the ecu?
Vee:
While it could very well be that the intake manifold gasket is leaking air, I do not believe the engine will react any different to that leak versus ant other vacuum leak downstream of the MAF, will it?

 

Nope, a leak is a leak is a leak. Before I took my car to get the adaptations reset on a real Jaguar PDU (Top Line Jaguar in Springfield, VA has one), I changed all coils with "Made in Japan" coils, EGR, spark plugs, CPS, TPS, Coolant Sensor, IACV, four oxygen sensors, both exhaust manifolds (one was cracked), camshaft gasket and probably a few more parts. I also swapped out my ECU with a known good spare I have.

Nothing fixed it. Nothing affected it. The PDU masked it for a few months, but it came back.

The only thing that managed to make it go away was replacing the intake manifold gasket. It took a shop a while to find the leak, and when they were done the 32 second dip was still there, but after a few days of driving it slowly disappeared. I credit the cars requirement to relearn as the reason it didn't get resolved immediately.

I was about ready to swap out the alternator as I began to suspect that the voltage regulator perhaps had gone awry, but the problem faded just as I was getting ready to make the swap. I was experiencing a dip in idle and amps as shown on the dash.

Coincidence perhaps, but I spent a year and a lot of time and a bit of money hunting this solution down. I'm going to recommend the intake gasket.

 

Best part of the intake manifold gasket is that it is not expensive and should be something someone with some tools and a driveway could pull off in a day. (Make sure to get that water rail hose changed while you're in there)

I had a shop do it because I was frustrated at the time, the summer was super hot and I didn't have a garage to work in.

 

I am on board that the intake manifold can do it, but also the cam cover, the hoses the TB, the vacuum hoses and so in. And of those, the intake manifold is one of the hardest to "see" a leak. I broke down and bought a smoke machine a few years ago and now intake leak frustrations are a thiong of the past!

So, are we surmising that the 32 second lope is some sort of time base for the fuel adaption?

 

I was testing the sensor by itself with the car running, electrical connector removed.

Hmmm, so by that measure, maybe the sensor is good and the meter just changed decimal places and that's where the 302 Ohms came from?

I got a lot of more reading to do....lol.

Bernie

 

Yep! KOhms are kilo Ohms, which are 1000 ohms, so .3 X 1000 =300.

You have your meter on autoscale, no doubt, so it is changing scales - including the behavior you mentioned in a previous post of it showing out of range, then changing. Sometimes it is better to set the scale manually when watching a changing value.

 

Vee,

That's a very interesting possibility.

Bernie,

The torque specification for the intake manifold fasteners is very low, just 21.5 Nm (16 ft. lbs.) to 28.5 Nm (21 ft. lbs.), so it's not uncommon for them to loosen over time. Before you go to the trouble of replacing the gasket, it might be worth simply retorquing the nuts and hex-head screws to the higher end of the range to see if the situation improves.

It would be prudent to follow the torquing sequence in the Workshop Manual, or at the very least torquing the fasteners in 3 or 4 steps working from the center fasteners outward to avoid warping the manifold.

Regarding the ECT specifications, here are a couple of data points from the AJ16 EMS manual that may help in your diagnosis:

At a temp of 86F the resistance should be 1.7 kohms
At 193F the resistance should be 0.25 kohms (250 ohms)

So based on your measurements so far, your ECTS may not be too far out of range, but since they're inexpensive it's not a bad idea to install a new one preemptively just to rule it out as a contributor to your symptoms.

Cheers,

Don