2005 s type 3.0 237000 mi.
Ok, New member, not my car. Here is what I experienced. First experience. Pulling into a parking space, Just about to stop when the car seemed to lose some braking and then did stop. Thought it wierd but didn't think much of it. Second Experience, Started car, shifted into reverse. Car seemed NOT to respond to pedal input at first so I lifted off of the pedal. I then applied pedal pressure a second time with the same result. I pressed the pedal a third time and came to a more normal feel of acceleration and proceeded to exit my gate. I placed the car into park, The a/c was on still running I opened the car door and closed my gate. I entered the car, closed the door And placed my foot on the brake pedal, I heard a buzzing noise so I turned the a/c fan off to hear it better. Thats when I noticed the tach at 2500 rpm. I tapped the gas pedal and it returned to normal idle. So now I feel there is a fly by wire issue. I continued on my way aware of this issue to pick up the owner of the car. I told my friend of this issue and we proceeded to return to my house. Third experience, at the third stop sign, coming to a stop, The car again lurched forward to 1000 rpm requiring additional brake pressure to stop. This is a real problem with the car and not a foot or a shoe. This seems to be dismissed by most as a foot or a shoe problem. There are so many complaints about this but I have not been able to find any real answers. Can anyone tell me from their own experience if this is an issue with the pedal assembly or the throttle body, Or cruise control? I would like to fix this issue before someone gets hurt. Thank you

 

Many of these symptoms suggest a vacuum leak. I experienced something very similar today, with erratic braking, surging idle, and poor throttle response. I've got a long-winded heartwarming story to share, but it must wait until tomorrow. I've got to turn in for the night.

More details about the car's recent history will help, too. Specifically, is the Check Engine light illuminated? Any recent repairs or other problems? Reliable daily driver? Temperamental garage queen? Something in between?

 

Thank you for the fast response.
I see now The error of my ways. A person could look or ask for a simple answer online when It could be just the basics. Vacuum affects power brakes.The rpm changing with the foot on the brake at idle was a "one of these things is not like the other moment". The other issues were during motion, so you depend on that vacuum, and as it leaks, it fails at a certain hg. air enters the vacuum when you need it most and the car continues its forward motion. Yes there have been recent repairs and service due to the high miles. Theoreticly I should be able to simply to hold the brakes on to repeat my second issue.
Good evening.
Many thanks

 

holding the brakes and some ether should be able to find an engine leak, and a booster vac test could follow that up

 

More details of what I experienced yesterday due to a big vacuum leak:

https://www.jaguarforums.com/forum/s...-p1151-254009/

My car is an '02, so some of the details are different, but the general idea is the same. Note how I experienced the engine speeding up while slowing to a stop, the seemingly poor brake performance, and the rubbery throttle response.

I'm not sure of your experience level, but please be aware when checking for vacuum leaks, you have to adjust your technique versus working on an older vehicle. The computer will instantly adjust fueling to maintain a steady idle speed, so you won't see a change if using ether, etc. On an older car, the idle speed would change, but not so with fuel injection. You have to connect a scanner to watch for changes in short term fuel trim. Details here:

JagRepair.com - Jaguar Repair Information Resource

 

This may help with the post face lift models:

https://www.jaguarforums.com/forum/s...ics-faq-52720/

 

Thank You For the link. I will be seeing the s type again next week. Perhaps we will find the problem at that time.
Thanks again

 

A smoke machine test revealed a leak at the quick connect air line fitting under the throttle body. Also there was an intake manifold bolt cross threaded. I replaced the bad lower manifold, all of the seals and o-rings. That fixed the vac leak. I then had to replace the maf sensor. A compression test revealed a low cylinder but not by much. With 230,000 miles, it runs nice.