So I live in Vegas. It just went from 110 degrees to like 40 degrees. My car runs great. No rough idle issues, choking, misfires. If anything it runs better. But im a semi mechanic still learning. What do I know? Here is whats going on.

As soon as it got cold the vehicle threw codes po171 and po174. Lean on both banks. Sometimes I get something about cold start and air\flow temp codes. Also seen something for coolant thermostat. I forgot the exact Codes. But those go away when car is warmed up.

I immediately checked for leaks and I changed all hoses O rings etc that connects to throttle body. All the small lines I changed except the long one going to passenger side wheel well and one going down beneath the coolant expansion tank. So I dont know if that line going down towards the bottom has a small leak. I also got a brand new MAF installed and it has lifetime warranty I even switch it three times to make sure it wasn't that.

All the intake elbows I gave it new hoses. In the past year I had the exhaust modified after the cat and im sure there is no leaks. And a K&N drop in filter.

What can this be guys? I do believe the O2 sensors are working fine. Is this a fuel delivery problem? I have a pretty high end scanner but I dont know how to read fuel trims\pressure or other graphs. Can someone give me the specs it is supposed to be at to help me narrow this down? Maybe clogged/dirty fuel filter or injectors? Its so confusing because the thing runs perfect. I still average over 21 mpg in the city. Even with the 20% or so more fuel being delivered.

My car is a 2009 XJ8L. The dealership said something about a PCM update and cleaning entire fuel system.

I will post pictures of what I did so far as to the lines I replaced. I appreciate any help or thoughts

 

Guessing here but you mention some fleeting code to do with thermostat. Could the engine be running cooler than it should for an extended period causing the 20% more fuel to be delivered?

However that, to me , begs the question about lean codes?

I am sure someone more knowledgeable will chip in.

 

Yes that code showed once. When it was super cold first start up of the Day. Seems like in this cold weather it takes forever for her to warm up. But she eventually does get to normal temp.

 

It is possible to get false lean codes via exhaust leak. If you have an exhaust leak veggie the o2 sensors it can trick the car into thinking you have lean conditions from air vacuuming into the exhaust system to be read at the o2 sensor. These tend to harken most when is cold and can go away when the car heats up.
I beleive in in the sand boat as you. I recently bought a party fog machine from ebay and hooked it up to my intake to check for leaks. I had very very little smoke from the brake booster clip which I hace replace a few times before. I went ahead and bought a new brake booster hose and clip to be safe. My next step would be to book up the fog machine to the exhaust avd check for manifold leaks. I do hear an exhaust leak especially when it's cold.

 

My car takes about 15-20 minutes to warm up when the ambiant temp is 40-50 degreesF.

If you have some way of measuring the temp either side of the Thermostat position you should get a much higher reading on the upside than the downside after 15 minutes or so. If its not much lower than the high side on the low side after that time then the thermostat cold be jammed open.

If this is not the problem than a leak is far more likely in the intake system.

 

The exact same happened to me last year. The thermostat wasn't closing all the way because the internals of the housing was breaking apart. If you are using your heat and driving early or late at night during tomorrow's cold snap with the car bone cold you'll definitely get that code again if that's the issue. It's not a fun job to replace but it can be done with hand tools if you are willing to put in the time. I'm a fairly experienced wrencher and ended up spending 6 hours on the job since I had to repair a couple of the skinny hard breather lines that snapped. The throttle body needs to be removed along with the aluminum neck that attaches the throttle body to the plenum.

 

Thanks you guys all of you. I will continue to try and locate the issue. If I get to the point where im going crazy I will pay the $600 to dealership. They said all they will do is a fuel system clean and pcm update. And use better gas. Wtf? I put nothing but Chevron Supreme in this since i've had her

 

So now its the two po171 po174 codes along with pending po101 and po50B

Im so frustrated what should i do. Also is it normal for the throttle body to make noise when engine off ignition on? Like a whine noise

 

I have no experience of this but it seems the codes are indicating a vacuum leak.

https://www.obd-codes.com/faq/fuel-trims.php

In the next link he states that you only notice small vac leaks

when the engine is cold and only using the MAF sensor.

.

Now all you have to do is find it!

 

po -> p0 (so you can search)

Lean codes do not have to mean an air leak but you can tell by watching fuel trims. Engine hot, parked, LTFTs at idle then rev to about 2500. If they were (say) over 10 and drop a lot you've an air leak.

 

Lean codes usually are a vacuum leak. A smoke test is an excellent way to find them.

https://www.obd-codes.com/p0101

 

No point trying that till fuel trims are checked not least because smoke test can miss actual leaks. If you have them, which the trims will tell. Let's get data rather than assume.

 

Evan,

I too am in Vegas and also have the same codes, but on an '04 XJR. I'm getting the car smoke tested tomorrow to find the cause. The weather our here seems to really mess with our cars! I'll let you know what they find...

 

Evan,

The Jaguar X350 Diagnostic Trouble Codes Summaries manual can be downloaded at the link below. It provides definitions and possible causes of each fault code specifically for the X350, so it may be more reliable than some of the generic OBDII code websites:

https://www.google.com/url?sa=t&rct=...03388427,d.cWw


Cheers,

Don

 

I was doing a little bit fo reading. Something to consider:
if Freeze Frame shows that a lean code set in open loop at low coolant temperature, Live Data allows you to watch fuel trim as the engine warms and goes into closed loop. A vacuum leak setting a lean code would be expected to show approximately 20% total positive fuel trim correction at idle. If fuel trim in Live Data shows no lean condition in closed loop at operating temperature, the cause of the lean code may be a temperature related vacuum leak, such as an intake manifold leak that seals when the manifold expands as it heats. Locate that vacuum leak, again using Live Data. Introduce propane around the manifold gasket and watch the oxygen sensor values. When the oxygen sensor data holds at a high voltage reading, signifying a constant rich condition, the source of the leak has been found.

 

I just posted this to the similar thread above that concludes the MAF might be the problem.

When I bought my 06 SV8 it had codes P0171 and P0174 - (lean condition on banks 1 and 2) and I drove it 600 miles home that way. At home I discovered that someone had failed to reconnect the hose from the PCV valve to the bib on the side of the intake tube. I reconnected it and have not had the codes since.