Hello.
This question is about my 2004 Vanden Plas. I have had the car around 4 years. 155k
I have had this issue ever since I have owned the car, and have never been able to figure it out.

If the outdoor temperature is over about 55 F, my car runs great and I never get a restrited performance warning. So basically, all summer long, the problem does not occur. However, once fall hits, and winter comes, and the temp is below 55F, I always get a restricted performance warning, with codes P0171 and P0174. The car runs fine, as long as you dont hit the 3k rev limit that it imposes.
If I feel like stopping, and clearing it, I can continue my trip usually without it returning until next time I start the car. But is consistent, it always goes away when warm out.

I have read a ton of threads, tried to find and fix anything I could think of. I replaced some rubber o-rings on the valve cover where there was slight leakage. I change fuel filter, air filter, checked for vac leaks, checked dipstick, changed spark plugs.......but no change in the behavior.

So, If anyone has an idea of what that is temp related could cause it, I thought I would throw the question out there. Maybe someone else has had a similar issue when cold out.
Thanks all!

 

Ace,
Check your coolant temp. You may have a leaking/lazy thermostat.
Live data will show coolant temp; should be > 190F
Engine running too cool can trigger lean fault codes, particularly when its cold out
If yours needs a new thermo, suggest use OE jag part, plus replace (plastic) thermo housing at same time

 

Not sure how to check it, inspect the connection? The temp guage always reads spot on, dead center. I replaced the overflow a while back.
Im assuming you mean the coolant temp sensor? If you mean themostat, its got to be good, engine always runs at perfect temp......
Thank you for the input.

 

From reading this forum P0171 is usually an air leak and people

have had success in finding it using a smoke generator which you

can hire from local auto spare shops.

 

Check out all the obvious sources for the leak.
Mine turned out to be the eight intake manifold gaskets.

 

Ace,
- My coolant thermostat (not sensor) was leaking internally, causing lean CEL in cold weather
- Check OBD Live Data for actual engine temp; your dash gauge will read centered even with slighty hotter/colder actual engine temp within a range - designed that way
- By all means, verify no vac leaks (but, lean code only with cold ambient temp is a strong tell)
- When verifying vac leaks, check especially brake booster/engine vac fitting, and PVC valve to valve cover o ring

 

+1 from hisport

Check everything else first

 

So you only get restricted performance in the cold. Is the check engine light (MIL) illuminated only in the cold or is that on all of the time? What I'm trying to determine is do you always have the codes and only restricted performance in the cold or do the codes and the restricted performance both show up in the cold?

 

The codes, and the restricted performance show up at the same time. Under 55F shortly after I start/drive car. Always before fully warm.
When its above 55F, both the check engine light, codes, and restricted performance go away. For the entire summer.
While I have a code reader and can clear them, they'll actually go away on their own if its warm out.
Thanks.

 

All good suggestions. I would also check your intake air temp sensor also. Since it is so consistent I would suspect a sensor of some type. If the intake sensor is off the MAF sensor is working on an incorrect calculation for the amount of air going into the system. The O2S and MAF will be fighting one another to correct your problem. LTFT will be skewed one way or the other.

 

I also have a 2004 VDP. Had the same problem. Cold I would get the P0171 & P0174. I hooked up a vacuum gage to the brake booster hose. The vacuum was low.
Engine warms up, everything expands and vacuum leaks leaks go away. Clear the codes and the car will run fine all day until the next cold start.

I smoked the engine and found some leaks. With a car that old and miles I would just replace everything.
So valve cover gaskets, intake manifold both the flat gaskets and the molded ones. As long as the manifold is off replace the valley hose etc.
I like to wipe a little Hylomar on gaskets and O rings. The tube between the air cleaner and throttle body has a sound box that connects to it with a rubber grommet. That grommet leaked. That was hard to find. Some leaks won't smoke with the pressure but will leak under vacuum. Some RTV around the grommet fixed that. This did not happen all at once. It took me some time to get to the point that the vacuum was correct on a cold engine. Got it all done just in time to store for the winter. Hopefully in April I will have summer of carefree driving.

As long as we are talking. If the trans fluid has not been replaced, plan on doing that. Get the metal pan, forget the plastic. As long as the pan is down replace the bridge seal and the 3 pipes. I use the Ford fluid. Lots of discussion on what fluid to use and how to flush it. I like my method that I have discussed in that thread.
These 350s are Fords. Source Ford parts, half the price of Jaguar. Upper A arms $150 vs $300. Front hubs Detroit axle $50 vs. $900 really. I assume the suspension has had the love it needs? I rebuilt everything. Bushings, struts etc. Maintaining and older Jag without going broke is a creative process. When everything is working is a beautiful car. Good luck.