I took my car to the mechanic because I had an erratic idle. He ran diagnostics and there were no error codes. He then took it for a ride and he experienced the same issue that I was having and suggested that it might be a throttle body/sensor issue. I couldn't leave the car with him because I need it for the weekend. Here are the symptoms:

1. I started the car this morning and it shut right off [then I started it again and it stayed on]
2. I started the car this afternoon and it was shaky...like it wants to stall out
3. It always seems to be hunting for the right idle [whether I am in park or driving]
4. Sudden surges in speed when driving
5. When I hit the gas it hesitates [whether I am in park or driving]
6. It doesn't seem as responsive as it should be..

I wonder why its not showing any error codes? What would you do next? In the past I have had to clean the throttle of other cars, is this the case with the xk?
I will be bringing it to the mechanic next week if I can't fix this myself.

 

At the very least, fair warning per the manual:
CAUTION: Do not attempt to clean the throttle body. The bore and the throttle



plate has a special coating applied during manufacture which should not be removed.





Without codes, it's a bit difficult. You could search for vacuum leaks

 

Cheap OBD tool with live data and watch fuel trims, will show if you have a leak.

 

I find it amazing that a modern car with all this technology wouldn't throw a code with all of these symptoms showing that something is clearly wrong. I will be looking for leaks for sure. Thanks for the heads up.

 

How many miles on your 2007? When was your fuel filter last replaced?

If you don't know, then the first thing I'd do is replace that filter. Rule out intermittent fuel flow caused by a clogged filter.

Old school advice from a former shade tree mechanic.

 

It is 2007 with 98K miles...no clue as to when the fuel filter was changed. I will get that done as well.

 

I filled her up with a fresh tank of Premium fuel from Exxon and it seems to be driving much better today than yesterday. Maybe I had a bad tank of gas... I am still going to take it to my mechanic next week to give it a once over.

 

I just started her up again after an hour of being parked and it died on me. Seems like its not getting enough fuel/air or maybe vacuum leak. I will let the mechanic look at it next week and report back.

 

Mine did this when i bought it, idling up and down, stopping at lights all your symptoms. Had the 2 air filters sensors even changed under warranty. Still no joy. Then at a car event i met a guy who do service work for all the top marques of car. I looked a the car and said he might try a retune. After a few days or so i left the car to his workshop as he did a complete service of the car including the gearbox transmission and rediff oil. As people have said many times you can't clean the throttle body on these cars, but he cleaned mine using a ultrasonic carb cleaner machine. He said it had a bit of gunk around it. He did do a retune and thankfully the car has never gone better and the engine idle problems and other issues stopped.,
Since then i've had the car remapped and The response after the remap is astonishing, he did a top pulley change also. Anyway i would get a tuner to give the car a good once over first. All these dealers just want the big bucks.

 

Does my 2007 xk have a throttle position sensor?

 

I'd have to say yes. I currently display it on my infotainment screen via my HKS Camp2 installation. I can watch the value change as I press the peddle.
It is a percentage value available via the OBD-II interface.

 

Again, being "old school", I'd do the cheap and easy things first. Misfires can be caused by something as simple as water in the gasoline. Adding fresh, uncontaminated gasoline to an already contaminated tank won't cure the problem because the water is still there.

Drain the tank as completely as possible, add a can of fuel conditioner that is labeled to absorb water, change the fuel filter, and add 10 gallons of fresh premium fuel. Drive on the highway for 30 minutes and see what happens. Hopefully, you'll get lucky.

 

I believe it has a throttle control system which is more sophisticated then the typical TPS. The early TPS was basically a switch which was either on or off whereas the present systems monitor the throttle position during its opening.Due to the nature of the electronics I would not try to clean any of it with a solvent cleaner .

 

Instead of messing with the throttle body, which is likely not the case and perhaps you'll do more damage than help, do as Stuart advises but take it one step further... at 100K you're due for a major service anyway so go through it and do the following:

Plugs (take a good look at each upon removal), air filter, oil and oil filter, cabin air filter, brake fluid, probably change out the tranny pan and filter, drain that gas as he said replace with fresh stuff and run a conditioner like Seafoam or other cleaner then drive it hard for a little bit. With the except of the tranny and maybe the brake fluid everything else is easily done with the need for a mechanic to confuse you and run up an unnecessary tab.

 

Agreed.

 

Update: Today I did a good ol' "Italian Tune-Up"....I took her out on the highway and drove it fast and hard for a hundred miles. I even used the paddle shifters for the first time...pretty slick indeed. It drove flawlessly on the highway and perfect around town as well. I am thinking that maybe I really did have a bad tank of gasoline. Which might explain why no codes were showing up.... I am going to get another full tank of Exxon Supreme and give it another workout during the week.


I looked over the maintenance records from the Jaguar dealer I bought it from and it shows that a full service was done recently so at least I know that much. As usual great advice and support from the folks here...very much appreciated.

 

I hate to sound like an *** here but why would you think that because a dealer says they did a "complete tune-up" would you believe they actually performed that? A piece of paper with a lovely letterhead doesn't mean it was done and done right. Taking that as gospel may be a costly mistake. FAR more than once I've made the mistake of believing dealers mechanics either did what they said or that they were competent in doing what they sad and it cost me a lot of $$$. A receipt does not mean they did it right. Cover your bases, like Ronald Reagan once said "trust by verify"... there's more to that then you'll ever imagine. My very first car I bought to a mechanic to have the clutch replaced and they botched the job badly lesson learned. I've had personal friends that were certified Acura mechanics that advised me on doing repairs that were totally wrong wold have cost me a LOT of $$$ not solving my issue.

Every time I've ever bought a vehicle I've ALWAYS gone through each one to assure myself that regardless of what receipts say that it was in perfect running order, FAR cheaper than allowing a single mistake and gives me piece of mind... this includes, motor oil, filter, air filter, cabin air filters, running injector cleaner, checking all tires air pressure including spare, retorquing all lug nuts, checking brake pads, replacing brake fluids, even if it shows it was just done.

There are usually not that many issues with these, or most, cars to take care of the known things and regular maintenance and you'll avoid 99% of the unforeseen things and it'll cost you very little

 

I followed your advice ↑ with my last car and it didn't do me any good.

I bought this car from a Jaguar dealer in Sarasota Florida. He sent me the service records and the CarFax before I bought it. Everything looked good on paper [yes, with the lovely letterhead], so I bought the car and had it shipped to me. The car drove excellent when I received it. Were they truthful about the service records? I don't know. Did they perform the work properly? Again, I do not know. Was there anyway for me to verify this before I bought it? Well, I could have paid an independent mechanic in Florida to perform a pre-purchase inspection which would take at least 8 hours to do correctly. But how can I trust him anymore than the dealer? Is he going to run full diagnostics on each component of the car? Will he send the oil out for an analysis to see if it the 'correct' oil? Will he pull each spark plug to verify that they are properly gaped? Will his findings be accurate or truthful?

The last 'expert' mechanic I paid to do a pre-purchase inspection on a Porsche that I bought didn't catch the radiator that leaked two months later. He also didn't catch the wheel bearings that started making noise after 6 months. He also didn't catch the shocks that failed. He also didn't catch the oil leak that started. He also didn't catch the clutch slave cylinder that failed...etc. He missed about $5,000 worth of work that I had to pay for. Is it his fault all of these items failed? No, it is not. Hey, crap happens.

Moving on, I then went to the Jaguar dealer of Morris county to verify that the maintenance that was done by the Jaguar dealership in Florida checked out. I also had my seat reprogrammed by them. They confirmed that all the work that the Jaguar dealer in Florida did was actually done. Am I 100% sure that they were being truthful. No, I am not. For all I know both dealerships could be lying about the maintenance. Am I going to look for a third mechanic to verify that both the dealerships are being truthful and that the quality of their work is top notch? No, I am not.

That is called 'analysis paralysis' and I don't have time for that. My 30 years with new and used cars have taught me this - all cars need repairs at some point. Period. When I bought the Porsche, all the service records were there, I did my own inspection and and I paid for a PPI and still - I had to open my wallet for some major repairs.

So when you say "Every time I've ever bought a vehicle I've ALWAYS gone through each one to assure myself that regardless of what receipts say that it was in perfect running order". Yeah, well I followed your advice with my last car and it didn't help. The Porsche I bought was in "perfect" working order as well ...until it wasn't. Welcome to reality.

 

I have cleaned the throttle body on my car, this was due to the car having similar symptoms as you describe. It had a low start up rpm, and would take a few starts when hot to get moving.

Removed and cleaned out the throttle body using carb cleaner which was safe to use on throttle bodies and the amount of gunk that came out was crazy, was around the opening and the plate itself so never giving a good seal. Since then It starts great, 2k rpm start up, which it hardly ever did before and it has never suffered from hot start problems since (8k miles ago now).

You can clean them (at your own risk) but just make sure it mentions that it's safe to use on throttle bodies that have a protective coating, just don't use a brush of any kind. I only used a microfibre cloth and sprayed the cleaner onto that and wiped the surfaces clean.

 

Fortunately, it is now working perfect again. I put in another full tank of Exxon Supreme and it is purrrring like normal.