Well after battling these codes (P0171,P0174 with Restricted Performance)for awhile I believe I have finally resolved the issue.

If you have these codes I would try to fix it in this order.

1) Check for air Vac. leaks. This is a common fault....if none found move to next step.
2)Check and clean MAF sensor. This also is a common fault for these codes. If you believe it is the MAF pm me I have 2 extra MAF sensors that I could send you to help you out and save you 70 dollars.
3)Check your air filter. Make sure it is clean and make sure oyur air box has a good seal.
4)Check your gas cap. This believe it or not can cause these pesky codes. Also I have a spare good working gas cap that may help someone if needed.
5) If all the above has checked out ok I am sorry to say it prob. is your Throttle Body. I would check around ebay for a good used one. I found one with 50,000 miles on it like brand new for $90.

So as you can see after I went through all the steps mine ended up being the Throttle Body. I have drove the car for several days with not a hint of P0171 or P0174 with restricted performance.

I hope this helps those with this problem

 

For whatever reason, these Jaguar throttle bodies are by far the most sensitive and tempermental I've ever owned. Even the slightest amount of moisture will shut them down. Ours had to be replaced under warranty at less than 30,000 miles due to moisture issues causing a limp mode situation that scared the hell out of my wife. She was ready to push the car over a cliff as a result and it took some serious convincing to get her back behind the wheel after the throttle body was replaced....

 

Check google and you'll see many other modern cars have TB issues. It's brought on by the ever-tightening emissions laws

 

Yeah I am not blaming Jaguar for the TB issues. I just don't think we get nearly as good a grade of gasoline as yrs gone bye. It would be nice is Jaguars sensors weren't so sensitive though.

 

I think my 1999 Dodge Ram's throttle body could handle everything from rainwater to melted lard without missing a beat. I didn't know that it's original O-ring gasket between the air filter housing and the throttle body had deteriorated to flaky dust until I removed the air filter housing to clean the throttle body for the first time about a year and a half ago. Cost me less than $2 for a new gasket at Advance Auto Parts and the truck has been running strong ever since....

 

Sorry but 1999 doesn't count as modern enough. Look for vehicles which are ETC (elec throttle control) aka drive-by-wire. Not happy reading

 

My dad's ride also threw that erratic codes , mainly 174 . After PCV valve replacement those codes were gone , happily and finally lol

 

John,

I'm not sorry, I'm glad (about my Ram, that is)! I'll take a real old-fashioned cable controlling the throttle body over drive-by-wire all day long....

 

So would I but it won't meet the newer emissions laws. (Generally they don't retrospectively apply so earlier cars don't need to be changed and can continue to emit more pollution.)

 

So you didn’t get the codes p0171 p0174 ?

 

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