I have a 2004 XJ8 Vanden Plas.

I have been getting a P171 and P174 error code. Its telling me the fuel mixture is lean on both banks. My mechanic suggested I clean the Mas air flow sensor. I did and still I get the message. Then I replaced it. With the new one installed I am getting the same error code now. So what else could cause the lean condition on both banks? One other thing on cold start the idol is rough like its miss firing. Once it warms up there is no miss. But the engine light stays on. I reset the code tonight and drove it to the store and back. The engine light didn't come on. Its about 10 miles round trip. I've done this before and the check engine light will eventually come on. Im thinking it wasn't the MAFS but something else. And last. Its telling me the engine performance is compromised but there is no evidence if a lean condition. No detonation at all. So what is this over engineered jewel trying to tell me?

M Ruddell

 

I've moved your question from Jaguar Forums Feedback & Suggestion Centre to X350 forum. This is the place to post technical questions about your 2004 XJ8.

Please update your forum Signature either to show this as an additional or a replacement vehicle.

Graham

 

I give up! How do I change or remove the signature that has my old car attached

 

Have those little internal intake manifold gaskets been replaced yet? There's eight of em, my 04 XJ8 was giving me fits till they were replaced in mine. Ran great, passed E-check tail pipe test with ease, but would throw the check engine light on, often after a couple hundred miles. Just when you think the last thing you did might have fixed it, the light pops on telling you no such luck, keep looking.

 

Use Search - but use the proper codes: P0171 etc. These codes are very common and all the causes have been much-covered.

 

It could be butter fly in your trottle body stuck open at idle.