At idle or very low throttle the car has surges in rpm. So much so that my daughter almost ran into a wall while parking. This change in RPM does not happen all the time just once in a while. I've been searching the forum for info on the cause but welcome your input as to the cause and fix.

Withthe car new to us I have a number of projects to work on - this is near the top...

 

Could be something flexing and making an air leak. Smoke test to find it.

 

Is there an idle air control valve on these engines? I thought it was all electronic via the throttle?

I would be having a look at the values for the pedal position sensor and the throttle position sensor in Torque. Maybe one of them is dirty and giving erratic values.

 

Hi evm,

Welcome to the Jaguar Forums! It's great to have you with us.

I have moved your thread from the General Tech forum to the forum for the X100, which is the Jaguar factory project code for your 2000 XK8. Here you will find knowledgeable owners of similar cars.

Off the top of my head, some of the potential causes of surging idle include:

Vacuum leak
Intake air leak
Obstructed air filter
Failed fuel pressure regulator
Failing fuel pump
Obstructed fuel filter
Contaminated fuel
Leaking/clogged fuel injector(s)
Loose/stretched timing chain(s) and/or broken tensioners/guides
Dirty throttle body / thermostatic air bypass valve (no separate Idle Air Control Valve on these)
Dirty or failing Throttle Position Sensor (TPS)
Electrical/electronic issues

Do you know whether the engine still has the original plastic upper timing chain tensioners? If not, add to the top of your project list removal of a camshaft cover to inspect and if necessary replace both of the upper timing chain tensioners with the upgraded metal-bodied ones.

Easy things to check first are to visually inspect all vacuum hoses for looseness, cracks, breaks, etc., and to carefully pull the vacuum hose off of the fuel pressure regulator and inspect the nipple on the regulator for signs of wet fuel, which indicates failure of the FPR diaphragm, and check the air filter for obstruction and the accordion pleats in the air intake pipe between the air filter housing and throttle body for cracks or crumbling plastic.

Cheers,

Don

 

Thanks All, I've got my list to check on now.

BEst

 

After the car sits overnight, cools down, and first start the next day, do you hear any noises from engine such as ticking or rattling? And after overnight cooldown and cold start in the morning with no throttle given after start up, does the rpm surge at all (hiccup, skip a beat, increase dramatically for a second or two then level out or stumble like its about to die but then even out)? If so to any of those symptoms you may need new timing chain tensioners/chains. My 97 xk8 had original plastic tensioners (primary and secondary) and they were cracked, allowing pressure to bleed out overnight, and when starting cold I noticed hiccups and sporadic high and low rpm’s while warming up, once warmed up I could hardly notice anything.

aside from that or intake leaks, check full load breather, a common issue. Post back on your checks and findings

 

Worse but better...

When we bought the car we did start it and listen for valve chain noise. We did not hear any then but the car may have been started prior to our arrival.

This morning we started the car and all heck broke loose. When turning the key to run there was a ticking coming from the throttle body. When started the engine went to about 4000 RPM and was shut down right away. Starting again cave the same, ticking then 4000 RPM. A push on the gas peddle brought the RPM down to about a fast idle. The engine would stumble down to a lower RPM and sound like one or more cylinders were not firing then back to the 1000 RPM smoother idle.

Of note we did not hear timing chain rattle as far as I could tell. We do have an engine fault symbol lit and the engine was in Engine Protect Mode with the common faults listed also. I do need to buy a Jaguar code reader - I do have one that has Volvo codes and may try that RSN (real soon now).

In an attempt to figure our more I located the ticking from the throttle body. Touch and wiggle the connectors brought me to the right side of the throttle body and wiggling the right forward connector changed the ticking and then eliminated it. The engine then idled smoothly and the engine limp mode and other messages were gone. Pressing the gas caused the RPM to advance smoothly. In short the engine was purring. THe engine check light is still on but I would expect that to stay at least for a while or until the codes are reset.

Not wanting to assume too much it may be that this connector (and all for that matter) needs cleaning. And hopefully that was the cause of the surges that get this thread started.

The car has 70300 miles on it and by the records I have had the throttle body replaced at 66431 miles in 5/3/2016. Part number C2A1444 ($3339 part, ouch!)

With the engine idling smooth and steady I poked around wiggling the full load breather and other parts with no change in idle noted. The FLB appeared to have good seals and a positive lock.

We are out and away from the car for most of the day so I will have to get back to it later tonight. Being new to this car and Jaguars in general I do need to read up on what and where everything is. For example - What does that connector do? THe engine is an AJ27.

As a side note Replacing the cam chain tensioners is high on my list. Likely I will get to it early this winter. First I need to build a garage so as to not be doing it in the snow. Also, need to come up to speed on sourcing parts that does not include a fee for armed guards when paying for them.

Thanks to all!

 

The connector could just be your problem. These cars tend to have any plastic connectors(especially under hood where they heat and cool every time you drive) go bad over time. The plastic parts become brittle and break if left alone for 20+ years. If fiddling with that one connector clears up most issues, try securing it firmly with zip ties, as well as cleaning both plug and socket with proper cleaner. When I changed my spark plugs 7 of 8 connectors broke the tab to lock it in place, so zip ties were used to secure them and prevent them from making weak contact or falling off

 

I would not advise driving the car until you get the cam chain tensioners upgraded.

they will fail without any warning. It will be a $5,000 fix then vs a few hundred dollars to replace them beforehand.

Z.

 

At the very least the secondary/upper tensioners which can be changed using zip ties rather than having to reset the timing:-

https://www.jaguarforums.com/forum/x...ion-how-37415/

I wouldn't drive the car (or start the engine) until they are changed.

 

I will get around to changing out the secondary tensioners soon. Parts are on order. I'm not as risk adverse as others so starting the car does not bother me. Clearly there is risk...

Currently rebuilding the front shock mounts and putting in new shocks. Then onto cleaning the throttle body connectors. I see that one does have a zip tie. I'll use some dielectric grease and start to test.

Best

 

Take care with dielectric grease to apply it only to the outside of the smaller/inner half of the electrical connector to help seal out water. Do not apply it inside the connector on the contact pins. Dielectric grease is an non-conductor or insulator, so it can cause problems with the low-level signals to and from the throttle.

Cheers,

Don

 

^^^^^^^^ THIS !!! ^^^^^^^^^^

dielectric grease is the most misunderstood and misused product in the automotive world.

When put directly on connector pins Any current that passes is in spite of the dielectric grease, not because of it.

Even manufacturers of it are (knowingly?) mislabeling it.

it works great to use a very small amount on rubber bulb boots or spark plug boots to seal out moisture.

But not directly on metal contacts..

I found that out the hard way a couple of decades ago when I used it in a headlight switch on a vintage Shelby GT-350. Way out in the country my light failed one night. The light switch had a built in circuit breaker, Which kept cycling on and off. With only the dash lights to guide me I had to take the switch off and apart and clean off all the dielectric grease from the terminals ( and I hadn’t used that much). From then on I was more judicious where I used it.

Z

 

Darn, what was I thinking bringing up dielectric grease... Almost as controversial as oil brand. But I am here and here are my thoughts.

Yes, dielectric grease is an insulator, but not only that it is a vapor barrier. And that is the point of it. It is intended to be on the contacts and be displaced by contact pressure and thus form a vapor barrier around the current/signal path. If the contacts cannot displace the dielectric grease then you have a connector problem, not a dielectric grease problem. Weak contact force will give intermittent or ohmic connection issues. Again the contacts are the issue not the grease.

In the case of my throttle body connector I need to get a look at it and find out what kind of seal it has if any. Being that wiggling it cleared the problem it may be that there is corrosion already. Or that it was coming loose. Or that the contacts are weak and old. If it has an O-ring seal then applying very little grease to the O-ring may be all that I might choose to do. If no seal then putting grease on the connector body (and thus sealing it) would be useful if there were no other openings on the connectors. Otherwise I would run the risk of trapping moisture in the connector.

Grease, no grease and where are choices made based on the connector type and what kind of place one drives and stores there care. Think salty coastal climate vs a dry and warm one.

Here is a link to a video that does a good job of encapsulating the topic.
Best!

 

I got to the throttle body today and pulled both the throttle position sensor connector and throttle motor connector off. Both looked clean and corrosion free. The throttle motor connector mounting bracket appears to have been broken. Just the mounting tab with no damage to the connector or shell. It is held in place with some RTV and a tie wrap. The throttle position connector was fine. After cleaning them and giving them a squirt of deoxit5 I reconnected them. Both connectors snapped back nicely with their locking tabs giving a satisfying snap. Pulling on them gave no play.

I tried to remove the throttle position connector a second time but the locking tab was doing its job. No wait! When removing the TPS connector the first time it came off easily with minimal force on the locking tab. When trying to remove it again it was much harder to deactivate the locking tab. I should have taken a photo before touching it. At this point I would say that the TPS connector was not fully seated and had an intermittent connection. I'm not saying that this was a smoking gun but it could be.

When started before this work I had an engine check light. After cleaning and reseating the connector the engine check light was out. I still have a red bar but I will assume that indicates there are codes. I've got to look that up.

I found out that an old ODBCII reader I have does not give and codes. It indicates a connection error to the car. I've got an Autel AP200 on order. I'll read the codes and reset to see what is current.

Still waiting on secondary cam tensioners and shock parts...

 

Got an Autel AP200 in today and read the codes.

P0121
P1111
P1799
SCP(J1850)
B1948

I went ahead and cleared them and ran the car for a few minutes. The codes remained gone and the engine check light dark. I'm in the process of rebuilding the front shock mounts so the car cannot be test run. SO I will have to wait on that.

I am speculating (Hoping, Wishing, praying) that the loose TPS connector disrupted the CAN bus and thus those other codes are spurious. Time will tell.

All of the parts to do a secondary cam chain tensioner replacement are in. There are 2 roadblocks - First I did request a quote from a local shop (Kings Cross) and it will be raining shortly and I have no garage.

As always comments welcome.

Best

 

For the codes see which ones, if any, come back when you have the car on the road again and take it from there. P1111 is the code to indicate that the car has passed all its internal checks and normally is the only code you have - it should come back after you have been driving the car for a while.

 

Hey man, good for you for thoroughly testing things and checking back with progress, hopefully what you did so far will clear your codes and troublesome issues. Sometimes “bush” or “backyard” fixes is all it takes, although frowned upon by expert mechanics who have all the tools and knowledge at hand to properly diagnose and fix things, but sometimes us regular folks can achieve the same results by doing something else not stated in the manuals and be just fine. Do check back in with your progress and cars running status when possible… and as far as the shock mounts your into changing go… what are you using for replacements? URO brand upper mounts? Or did you source some polyurethane mounts from users here like phobmans or baxtors? If using URO ones, PLEASE take a moment to search the threads for all the horror stories documented by others who’ve went that route. I originally purchased URO brand upper mounts and luckily was able to obtain a set of phobmans mounts which I used instead. Not saying they won’t work but general consensus seems to be that they will fail, sometimes within weeks or months. I read so many bad things I took a 90 dollar loss after purchasing and couldn’t return to go with polyurethane ones. Just saying, not all replacement parts are created equal

 

Stevis05, thank you for your kind and encouraging words. I spend more time searching than posting so I was able to figure out that URO brand upper mounts were trash. I did source some polyurethane from phobmans. They look great! Just waiting on the delivery of a set of bump stops to get the shocks reassembled and back into the car. New shocks too as that I did not want to rebuild the shot lower mount and with new Bilstein's I hope to never pull them out again.

Too often the experts disdain for us non-professional is the protection of an income stream. I'm here for the love of cars. Besides the tools and training the other thing that they have going for them is experience. A forum like this one is chocked full of experience and goes a long way If one simply asks questions.

Speaking of the forum - The forum and everybody's posts have helped me along so I write about what I am doing and learned so that others can avoid my mistakes and hopefully learn from me. I would be very happy if one person read something I posted and went Aha,

Best!

 

Just got a quote for a shop to do the replacement - $3000. Looks like I'll be doing it myself. Parts are in hand, threads read, now just waiting on good weather.