XJ8 Rough Idle - Stall - P0171 & P0174
 

Just an FYI in case this happens to you.

Car runs rough then stalls -- trouble codes P0171 and P0174 = Lean mixture both banks.

Cause was the sound attenuator on the air pipe just broke off. The "air pipe" connects the air cleaner to the throttle body. It looks like it was broken previously and glued back on. (Always dealer serviced so it is kind of surprising they would have "repaired" a $45 part rather than replace it if they broke it.)

Fortunately I had noticed the "glue" and a crack previously and had ordered a new part that I had in my trunk, but just didn't have time to replace it.

I think this is a problem for normally aspirated engines only -- I don't believe the supercharged engines have the attenuator hanging off the air pipe.

got a pic? would like to see it

I'm traveling this week for the 4th of July holiday. Will post a couple of pictures when I return.

Air Pipe Pictures:

Attachment 4258

Attachment 4259

Attachment 4260

I was looking at purchasing a '99 XJ8, and he told of an issue he had stalling and his solution.
He told me the issue was the throttle body. The throttle body would get flooded with fuel and not be able to "breathe." His solution was to spray brake cleaning fluid, i.e. "automotive chicken soup," into the throttle body every 6 months. Perhaps you could remove the plenum and take a look at the throttle body (3 screws if memory serves). If it's soaked in fuel, that might be your solution. I believe the throttle body is going to be underneath the plenum you removed, at the part closest to the firewall. I believe two screws hold that end of the plenum. Best of luck!

Fuel should never be anywhere near the throttle body - the engine is multi-point fuel injected down by the intake valves. He was doing a good job trying to sell the car.

Didn't seem to make sense to me either. But since I don't know the engine. . .
Ended up not bothering with the car. Too many little issues. Would rather stick with a solid runner with no mechanical and cosmetic issues.:icon_wink:

Fast forward eight years / 25,000 miles and the sound attenuator on the air pipe broke off again. It looks like this piece is glued on as OEM, so I decided to try and glue it back on again instead of order a new part. I noticed the symbol <PP> on the bottom side. With some on-line research I found that <PP> stands for Polypropylene which is a type of plastic that handles the high temperatures of the engine bay well, but is hard to repair. Most plastic glues actually warn you that they are not good for bonding polypropylene or polyethylene. I found one that said it would work: Loctite Plastics Bonding System (all plastics, all materials). It says it "Fuses hard-to-bond plastics". It has an Activator and a tube of Plastic Bonder glue. It worked very well and seems like a solid repair. I'll post again if it fails.

Interesting, who would have thought that part would be susceptible to breakage.

And over 8 years later that part is still only $42.00
https://www.jaguarmerriamparts.com/p...&siteid=215718


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If you look at the joint on the original part, it really doesn't look like a quality connection. It looks like a six year old put it together. I opted for the $3.77 glue this time instead of the $42.00 OEM part. The OEM bonded joint probably fails because PP is hard to glue effectively.