Last Summer my 01 Jaguar XJ8 was causing me all kinds of problems. Everything from sluggish acceleration or erratic acceleration, engine lights, not starting..I did a number of things to the car. I changed the spark plugs, MAF sensor, fuel filter, fuel regulator, both knock sensors as well as the water pump (was majorly leaking). After all that, the car ran like a hot damn! The cause of the car not starting was the fuel regulator, the engine lights were caused by BOTH knock sensors/MAF and the poor acceleration was the MAF sensor (I knew this since as soon as I changed it, it was like night and day). Winter came and went and now the car is not performing great again. Really has no guts when it comes to accelerating. Is it possible the MAF sensor is bad again? I put my old one back on and it is noticeably BAD! Any other suggestions? I've cleaned the MAF as well as the throttle body.

Currently, I do have a coolant leak (cannot locate it at this point), I do have an oil leak (also cannot locate) and there is a noise which I believe to be the transmission. I'll post a link to my video.
As always, any help would be appreciated. I've put so much time and money into this car and it's always frustrating when something else happens .

Thank you!

 

Sorry to hear about your frustration, especially when you seemed to be on the up. For the video I hope someone else can chime in on this, but that sounds like either a bad engine mount or transmission mount?

Was the car in storage? If so, did you put a fuel stabilizer in it? I would try a hard reset (undoing the battery cables) and see what she does. I suspect a bit of bad fuel initially.

 

I'm going to get a better video to reveal the sound it is making, I know that one is not great . Car was not in storage, drove it nearly every day over the winter months. I work from home, so the car really is only out an hour or two a day. I've tried the hard reset with the battery cables, to be honest the car SEEMED to run a little better after that, but has resorted back to bad behaviour. One thing I forgot to note in the OP, is that when coming to a stop the car will shutter a little. The RPM will slightly drop and then go back to normal. This isn't every stop, but it is frequent.

It was very rewarding last summer to figure out all the issues and get them fixed. I had a few good months of driving .

 

This sounds like an air/fuel mixture issue and it could be as simple as a vacuum leak. Be sure to check around for one. This says vacuum issue because when you apply brake, your engine is choking.

 

You need to start monitoring the fuel trims mafs and temperature while you're driving. A elm 327 and phone app like torque or an inexpensive code reader with monitor capability. I don't have a smart phone so I use an Ultragauge.

Then you can relay the information here so that others will have a better understanding of the problems. The fuel trims especially will reveal air leaks and mafs problems.

 

Totally agree, check the spark advance as well (Leaking coolant and knock sensors don't like each other - no idea where ur leak is though).
Advance should run all the way from ~4 degree at idle to ~30 degree at acceleration / higher revs.

 

Just to add to the excellent replies you've already received, I couldn't hear the video very clearly on my laptop, but since low transmission fluid is sometimes associated with stalling when slowing to stop or to make a turn, and you have what you think is a transmission noise, it would be worth checking for transmission fluid leaks around the pan gasket, electrical connector, cooler and cooler pipes.

Often poor engine performance is due to multiple components misbehaving, so it would be worth starting with basics like the air filter, and replacing the fuel filter just in case you have some bad fuel as Highhorse mentioned. Add a couple of bottles of Heet or other brand of gasoline dryer to the tank. A bottle of good fuel injector cleaner in the tank might be worth a try also.

You really do need to scan for diagnostic trouble codes and watch your live data as RJ and Eric suggest. Report any codes here exactly as they appear, along with your Short-Term and Long-Term Fuel Trims, and you'll get lots of help.

Cheers,

Don

 

Thank you for all the replies so far! I've gone ahead and ordered the elm 327 and it should arrive tomorrow . We shall start there.

 

The elm 327 arrived today and I'm a pretty tech savvy person but man oh man these apps are confusing. I'm using an iPhone, can anybody recommend a good app to use with this device? Not entirely sure how to even monitor the fuel trims. I've tried a few different apps. Thank you x3000.

 

I managed to get this information from Car Scanner Pro for iPhone. Is this what I'm looking for in regards to fuel trims and MAF sensor? Thank you everybody.

 

And here is the short term.

 

It would pay to read other posts. There are plenty about such as trims. They explain what they are, how they wor, how to test.

You want easy to grasp data.

Get engine hot then park. See what LTFTs are. If they're further from zero than about 5 try revving to about 2500 and see what they do.

Read MAF at idle and see if it's sane.