A couple years ago I had the dreaded lean codes and chased down a lot of leaks including replacing the eight upper plenum ring gaskets, the two lower intake manifold gaskets and other gaskets, o-rings etc. to finally get it sorted and running well again. However, lately it started to run poorly when started from cold, but would run normally once warmed up. Lately, it seems to be running poorly even when warmed up with lean codes and fuel trims suggesting an intake or vacuum leak.

I set up my homemade smoke machine and smoke is coming out towards the left side of the back of the engine. Any suggestions of where/what the leak could be coming from?

Thanks for the help!

 

Have you tried to read the error codes again now? If yes, what did you get?

On the supercharged versions, the brake booster is connected to the engine on the left side of the back of the engine. If it is the same on the n/a engine, that could be a possibility. The connector of the vacuum hose to the brake booster can fail because of an internal o-ring that gets fried with time.

Best regards,

Thomas

 

Thank you, I think that might be it because it was hard to reach I didn't touch it when I was chasing leaks last time around. Does anyone have any suggestions on how to get to it to replace the O-ring?

 

Update: Trying to find my leak I used a borescope to see if the smoke was coming from the brake booster vacuum line, but it turned out that was residual smoke coming from somewhere else and not that vacuum line.

It took a few attempts of starting the smoke machine looking for leaks, stopping to let the smoke clear, repeat, etc. to pinpoint where the smoke was originating. It's coming from the Throttle Body spring. In order to see it clearly I had to actually be staring at that spot when the smoke machine first started. Does that make sense that there would be leak at the spring?

Thanks for your help!

 

Has anyone seen or experienced a leak in the Throttle Body itself?

I'd like to verify before I spring for the cost of a new Throttle Body.

 

Without looking I believe that the spring is on the butterfly shaft
and I am guessing that the hole that the shaft goes through is
worn and leaks air into the engine.
You are very lucky in the US because you have a choice of used
parts dealers and can buy without paying horrendous shipping charges.
You may be able to buy one from a fairly low mileage engine.

 

This is spooky, I just searched the forum for the same issue having found the same problem today on my 04 XJ8. I couldn't find any other mentions of it, but yes I'm having the same issue.

A few slight leaks around the intake manifold but the spring on the butterfly valve shafted seemed to be the main leak source for me too.

 

Interesting! I wonder if there is some age related failure since ours are both '04 cars. There are much higher mileage cars who haven't reported the same so perhaps it isn't a simple wear issue. Thanks for replying.

 

My 04 XJ8 has started having very similar issues reciently with cold starts.
Misfiring with 171&174 codes then smoothing out when warmed up.
Having chased & replaced the same parts as you in the past Mac, those eight seals finally did the trick.
Thought the injectors might be causing the present lean issues, but were not the answer.
Guess i'll try looking for a vacuum leak, by using map gas next.

 

To give everyone an update and to close out the thread, the leak at the throttle body spring was indeed the problem. I don't like throwing parts at problem so I wanted some assurance that a throttle body itself might be the cause of a vacuum leak, I called a local shop that specializes in Land Rovers and Jaguars and asked if they'd ever seen this issue, and they said, "yes, but it is rare. Usually there are other problems with the throttle body before we see leaks."

BTW, the cheapest supplier for a new throttle body I could find was Jaguar Classic Spares. It was quite reasonable because they were having a 20% off Spring sale, and cheaper than some used ones listed on eBay. I contacted them with my VIN to make sure I was ordering the correct part. Shipping was reasonable and fast, it arrived in only 3 days!

 

If anyone wants my old throttle body to refurb or pull the TPS etc. I'm happy to give it away if you cover shipping costs.

PM if interested.