I have a 2003 Jaguar S-type 4.2 V8. I have had a diagnostic test completed by 2 different shops and neither were able figure out why the error codes were being thrown (171),(174) and (1,000). I have read in several threads to have it tested for air leaks and that my O2 sensors were bad. I pulled all 4 O2 sensors and all tested within required specs. I have rebuilt the transmission. I have replaced the electronic throttle body after noticing some smoke. The codes go away for about 5 miles the come back on. Does anyone know if these are simply phantom codes or is there a legitimate problem I should look into?

 

Stop throwing parts at it. Don't go back to the shop.

The codes are P0171, P0174, P1000. Use those with this forum's Search and you'll see what to do, starting with fuel trims.

The two lean codes are very common on modern cars (up to about 20 yrs old) so any shop should know ALL about them but clearly yours is clueless.

 

Yes you have a vacuum leak and it's common to both banks. Inspect the intake tubing carefully. With age the plastic bellows will often get holes and they are not that obvious to see.

Inspect the plastic tubing on the PCV system for the same problems.

P1000 is OK and just means you have cleared the codes and the car is NOT in the ready state. This means you can't pass smog inspection now but driving around will set the monitors.

Keep at it your are doing the right thing we just have not found your problem yet!
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Check hoses (smoketest) and easy to do check/clean VVT O Rings (AJ82856).

Gl finding the leak.

 

As you've no-doubt discovered, P0171/174 are fickle mistresses. This whole thread is chock-full of good advice, but the link in particular is to a post describing how I resolved the problem. I found the advantage of a spare S-Type with a high degree of similarity to the problem one a most helpful tool:
https://www.jaguarforums.com/forum/s...e3/#post867207

First steps should always be a close visual inspection of the engine's airway between MAF and Intake manifold, followed by graphing fuel trims at idle and elevated (2500?) rpm. Only after eliminating any signs of vacuum leakage through these steps do I recommend venturing into part substitutions. Don't forget that the oxygen sensors sense "Oxygen" (I know, right?) so any air-leak in your exhaust system upstream of the sensors will appear to be excess Oxygen and cause lean codes.