Hi y'all! I have a recent problem with my 2000 3.0L SE. It has developed an intermitent stumble on acceleration that has gradually gotten worse. There are no associated computer codes. It seems to run and idle OK under low load situations.
I suspect a small vacuum leak, possibly the breather elbow in the rear and under the intake manifold as this is a known potential problem and I have never replaced it. My plan is to check the vacuum lines, IMT vlaves and intake manifold. If I don't find anything I plan to remove the intake manifold, replace the sparkplugs and check/replace the rear breather elbow.
I was wondering what the S-type gurus think about my problem and if you think I'm on the right track. Also, has anyone else had similar symptoms and if so what was the cause? Thanks for the great support from our many helpful members. I'll post my results so othrs can benefit from my experience.

 

+1 on vacuum leak or one or more intermittent misfiring coils under load. (Might not necessarily flag the CEL)

 

Get an OBD tool with live data and check LTFTs (see my sig) in P at idle and 2500rpm (post here if you like). Will tell you if it's an air leak.

If coils, will probably be bad at 50mph uphill but do the OBD stuff first. Elm327 about $10 on amazon

 

Without codes it is hard to say what is going on. Plug your OBDII reader in and drive the car and make it stumble chances are you will capture a temporary code that will put you in the right direction.

 

Thanks! I knew I could count on some great advice on diagnosing precisely what is wrong with my S-type. I'll try getting the OBDII info and post what I find.

 

I hooked up my UltraGauge and checked the Long Fuel Trim readings: at idle bank 1- 11.72 , bank 2- 10.94, when when increased the rpms to 2500 the readings dropped to 3.91 on both banks. So if I interpret this correctly, it indicates a vacuum leak. Still no codes even when the stumble occurred. I plan to double check the accessible vacuum lines and if I find no leak source to proceed with the intake manifold removal and the dreaded breather elbow replacement.

 

Throws codes at about double that but best to fix it now.

 

On my car the leaking elbow threw codes until I replaced it. Take your time and see if you do have a leak and if not it could be something like a MAFS but try to narrow it down. I am no expert in reading fuel trims and when I think I got it I find I do not. See if this helps!

Link JagRepair.com - Jaguar Repair Information Resource

Link to my elbow replacement JagRepair.com - Jaguar Repair Information Resource

 

Update: I removed the intake manifold , checked the lower elbow and found it was OK. I replaced the sparkplugs and put it back to together. I found I was missing a bolt on the EGR to the manifold and replaced that.
It now runs about the same, still with the intermitent stumble, particularly with a moderate load. The LTFTs are now much higher in the 40's at idle dropping to the teens on acceleration. This has caused trouble codes to to be thrown: P0171 and P0174, both banks too lean. I checked the intake vacuum in between the throttle body and the the MAF: ~17" and steady. No vacuum leaks I could detect between the TB and the MAF. I tried cleaning the MAF with some spray. I checked and found it still running the same with high LTFTs (40+ at idle both banks). I checked some other things with my Ultragauge: fuel pressure @ 36-40 psi-OK , O2 sensors output functioning OK, MAF showing changes with throttle position but I can't tell if its good or not.

I found some info on testing the MAF while the car is running and will try that.
I also found some resistance values for the COPs and will test the 3 accessible coils to see if I find a problem. From what I read this still may not rule out a faulty COP that allows a misfire under load. I'm not seeing or hearing any sign of a vacuum leak but there are a vacuum lines and they are challenging to check for a small leak.

I want to find out exactly what the problem is rather just making assumptions, and trying to throw parts at the problem. Any other suggestions?

thanks again for all the great advice from the gurus: JagV8, GUs and Abonano
You guys are awesome!!

 

If the LTFTs head down like that I reckon you have a leak. It's bigger than almost any ever posted in the years I've been on here. Possibly the biggest.

You're down to finding it.

Bad coils or MAF wouldn't explain it as why would the trims head down?

 

Call your local garage and ask them if they can perform a smoke test on your car then make an appointment. If you have a leak you will find it then.

 

Gus and JagV8 , thanks for your prompt and helpful replies! I got way more aggressive in checking for a vacuum leak. I sprayed brake cleaner around the manifold and the lines but I didn't notice a significant change in idle. I then used a stethoscope to listen around and found some hissing from the under side of the EGR valve. Tomorrow I'll try to block off the EGR and see if this changes the LTFTs.
thank you, Vic

 

I removed the EGR valve and retested with its port sealed: After a bit of running the LTFTs dropped to 0!!!! Success!!! At first I was worried because initially the LTFTs were still elevated but after idling a bit they dropped to 0. I'm very glad that the gurus ( JagV8 and Gus ) jumped in to redirect me to the more likely source of the problem being a vacuum leak. Thank you very much, you guys are awesome!!
I ordered a new EGR valve and I'll update you all after I install it.

 

VMV

2 thing of note for the future.

The electrically powered throttle (TB). Carefully note the grime at the entry port just behind the butterfly where EGT slime enters the TB. You mentioned spraying it with a cleaner. These can be more problems if not specifically matched for this vehicle. They can effect the sensitive electronics and cause a premature failure of the TB.

False air or any air introduced behind the TB will cause a weak mixture that if not corrected can cause drivability issue up to and including engine failure. So treat that kind of problem with care.

Good Luck

Robert

Inspect transmission cooler lines above the air deflector for rubbing, as they will fail there if not inspected....

 

Thanks Robert! Good points, I did use a throttle body spray to the TB. The vacuum leak from my EGR while small and difficult to detect had a huge impact on my LTFTs ( into the 40's at times. )

 

I installed the new EGR valve and drove the car around with the Ultragauge attached monitoring the LTFTs . Initially they were still very high but gradually after driving a few miles they began to come down. The stumble on acceleration and under load is now gone. Kudos again to Gus and JagV8 for their great guidance in helping me to diagnose the problem.

 

Good to hear - thanks for the follow-up!

If you want to get it down faster - and you do not need to - disconnect battery for a few mins. It loses the learned fuelling. But it's relearning as you can see.

 

Thank you for reporting back! That's the only way we can find out what works and what does not.
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VMV - May I ask how difficult a task it was to change out the EGR valve and how expensive was it? My apologies if these topics have been discussed elsewhere.
Steve

 

Thanks! After all the great support I have gotten from this forum the least I can do is to report back on what has worked and what hasn't so that others can learn from my experiences as I try to learn from theirs.

Steve, Changing the EGR valve on my 2000 3.0 L was fairly simple just removing the 2 bolts that connect The EGR to the intake manifold, pull off the vacuum line and remove the EGR from the the steel line that connects it to the exhaust manifold. You have to wrestle it around a bit to get access to the securing nut at the base of the EGR but definitely doable. It's much easier than removing the intake manifold.