I thought I might find the solution to this problem and post it, but no such luck. I'm getting P0171 and P0174 codes and restricted performance. It's happening more and more often. I have an UltraGauge in the car and I am monitoring fuel trims. The LTFTs sit at max (19.53) at idle and the STFT fluctuates, but often goes into double digits - and this triggers the codes and RP. I've checked every hose, sprayed carb cleaner around, shot propane around, listened everywhere. I can't find a vacuum leak. I broke down and replaced the intake manifold seals and the throttle body gasket. While apart, I blew through every hose and examined the intake trunking over and over. I ran some BG44K injector cleaner through it. The fuel pressure is good and the fuel filter is relatively new. I always use branded premium fuel. The car runs flawlessly, idles smooth as silk. The fuel trims only go high when at idle (tick over). I got another MAFS off eBay and tried it - no difference. I got another evap purge valve (also used), and it made no difference. I'm running out of possibilities. One thing I just thought of though, I believe I pulled the dipstick out (after reading the excellent fuel trim write-up I found on here) and I don't believe it made any difference in the STFT. I also unscrewed the oil fill cap and don't believe it made any difference in the STFT. I'll have to verify this. But, I'm getting down to cam cover crack maybe ? Any ideas appreciated. Sorry for the long post ! TIA.

 

Wow, Jim. It sure seems you have about covered it from my perspective. Other than the thing you mentioned next, I would try and read the ecu voltage with a scanner with Jag extensions (injector pulses are modified with voltage level) and I might consider the remote possibility that the used MAF had the same failure as your original one. You did clean the MAF sensor, right?

 

Did you set the "Force protocol" on the Ultragauge to (I think) 9141, or a very similar number? If not, you will get all kinds of crazy codes.

 

Have you verified that the O2 sensors are working properly? A constant lean read from a sensor could force the rich long term settings.

 

If you suspect a major vacuum leak maybe a smoke test at a shop is in order.

 

Well, I did try cleaning my MAF before trying the used one off eBay. I have forced protocol on the UltraGauge and it's working fine. The only problem is the UltraGauge won't read the wide band O2 sensors. The one thing I can correlate sort of with when this started occurring is that the wife had an overheat experience a couple of months ago - cracked rad on a curb. I replaced the rad. Now I'm thinking maybe the heat caused a cam cover to crack or warp. I'm thinking I'll pull the part load breather and plug the pipe and see if the STFTs come down as a quick test before I get into big money.

 

If the LTFT is high on both banks, then the O2 sensors on both banks would have to be similarly malfunctioning. It's of course possible, but a bit unlikely..?

 

Okay, I smoke tested it and found a leak. I searched the internet and utube and found a way to make your own smoke tester. I won't go into it, but it involves a rubber hose attached to the part load breather tube, a rubber glove and a cigar (I had them laying around anyway). Sounds a little kinky, but it worked. The leak is coming from under the front left of the intake manifold. I can see the smoke and hear the hiss, but I took the intake off and examined it and could not see anything. The only possibility is the I.M. So I found one on FleaBay and ordered it. It's got to be a result of the overheat incident the wife had a month or so ago. I should have the I.M. and new seals soon. I'll finish this thread off (if it kills me!).

 

I love the idea of a Jag smoking a cigar-you should put a monacle on the windscreen for the full English Country Gent effect

 

Okay, I'm finally going to put this one to bed. We had some nice weather yesterday, so I replaced my intake manifold and fixed the problem. After a hard reset the fuel trims are finally looking normnal again. I got the IM off eBay for about $100. I also replaced the IM seals and rubbed them down good with vasoline. The IM leak correlates (sp?) with the over heat episode when radiator got smacked. Happy cat now.