'08 S-Type 4.2, been running great. Last night I filled up (about 2/3 of a tank of 100% gas, premium, same place I always use). Last half mile home fine. Start it today and it's idling fast. It settled down, so drove a couple of miles to the store. Two more stops on the way back; after starting up from the last one it seemed rough. Ran rough, erratic, hesitant, surging throughout the mile trip back home; CEL came on. Pulled codes, got P0171 (Bank 1 too lean, pending & confirmed) & P0174, Bank 2 too lean (pending). Could this just be bad fuel? The car literally has done nothing but sit in the garage since yesterday evening. Give it a shot of Dry Gas, maybe?

 

look at your fuel trims to confirm it has a leak , and make sure all sensors are with in perimeter via OBD2 as well while your in there .

 

Unlikely the fuel. Probably just that a leak or some other fault causing those codes has happened. Use Search as they are common and fixes etc posted often.

 

Check the two VVT O-ring seals for seeping oil running down below them. These two seals sit there and bake in the engine bay heat. After a few years they tend to get brittle and begin to leak oil and air. When this happens, the P0171 and P0174 codes often show up. If these seals are leaking, replace them with decent quality new ones. Some aftermarket seals are better than others....

 

+1 on checking fuel trims.

Check also for vacuum leak(s) between MAF and throttle body.

 

Have you messed around with the intake at all lately? Those two codes are most common with those who installed elbow intakes..

 

No. The hell of it is that I've done absolutely nothing to it lately. I drove home from work, put the usual premium no-ethanol gas in it, parked it in the garage, topped it up with oil, left the oil cap off, drove it a few miles the next day without the cap installed and all hell breaks loose. I've since installed the cap, test driven it a bit, idled it for a total of half an hour without event and driven it around at city speeds tonight without event. Then punched it a bit and created a smoke screen. Pulled codes a mile or so later and they were clear. I'd say it's a head gasket, except it acts perfectly normal until you ask for some power. If oil were getting into a cylinder I would expect it to smoke full time. I'm stumped. It's going to the dealer, one way or the other.

 

If you left the cap off it may be the cause. Drive it a few more times and the faults may be gone. Don't keep clearing them - it takes at least 3 warm ups for it to see what's happening.

 

+1 I'll bet that's the cause ,

 

The overarching problem is oil smoke - tons of it when you kick it. I thought I posted about that separately, but don't see it. Just yutz around at 30 mph and it seems fine. Ask for power and it blows horrendous amounts of smoke. As far as I'm concerned it's had plenty of time to clear any oil remaining from the cap fiasco (yes, I did drive it a few miles around town with the oil fill cap off). Half an hour of idling since then plus maybe 5 miles around town at low speed. Having it towed to the dealer shortly.

 

Canceled the tow, decided to drive it around gently for a bit and see how it did. it did fine, ended up at the Jag dealer 20 miles away (was scheduled for a brake booster replacement before the missing oil cap fiasco). Apparently it just takes a good bit of light to moderate driving to sweep all the oil out of the throttle body and intake manifold. Lessons learned, foremost being don't forget to put the oil cap back on.