Back in April, after a long winter, I took my car out of the garage and turned the engine on. The car sprang to life and I figured I’d let the engine idle for 10 mins or so to properly warm it up. After several minutes the check engine light came on with the dreaded RP message brightly glowing in the dash. Having watched an episode of Wheeler Dealer, where Ed China fixes an XK8 with an RP problem, I got worried that my car too, developed a case of throttle body gone bad or dead. However, after a few more mins of idling, the message went away and the check engine light turned off. Wow, I thought to myself; that was close – probably a case of those electrical gremlins that Jags are so notoriously known for.
Fast forward several months and a few thousand miles of trouble free driving, the light and the message came back, after a spirited drive from the Hamptons. Pulling off the freeway and on to a gas station, I shut the engine off, so that I could pump some gas. Upon starting of the engine, BAM!!!, CEL and RP message came back. After a few miles of highway driving, the RP message went off but the CEL stayed on. The car drove perfectly fine, the engine working smoothly as always – I didn’t know what the problem was. And thus has begun the adventure of finding the RP culprit. Pouring over this forum, I began searching through dozens of threads and articles on possible causes of my Jag’s infliction. There was so much info out there that I figured first I need to buy an OBDII scanner, which I immediately did - on the net. The generated codes were P171 and P174, which meant the engine ran lean. More reading on the forum I learned that the cause of this phenomenon may be due to:
- Bad fuel pump
- Clogged fuel filter
- MAF sensor
- K & N air filter, which I had recently installed
- Oxygen sensor
- Air leak in number of rubber hoses
- Air intake duct
- Evaporative purge valve
A peculiar observation made me notice that after erasing the codes with the OBDII scanner, I could drive indefinitely without the codes coming back, until I would turn the engine off and then start it again, while the engine was still warm. Another observation was that the codes were not coming back as quickly if I drove the car in a regular, non-sport setting. The moment I engaged the Sport setting, the codes were back. Furthermore, the RP message would go off if I switched the Sport setting off. I called up the dealer and a few mechanics, who unanimously told me that 99.9%, the culprit is MAF sensor. This forum here has many threads on MAF sensor replacement/cleaning techniques and I decided to clean the MAF sensor prior to replacing it.
Taking the MAF out is not an event worth writing about, since many have already done it here more than once – and thank you all for making it an easy DIY job. After 20 minutes I had the MAF and contacts clean and back in the car. I reset the codes and for a week or so, I was very proud of myself, because the lights, codes and messages were at bay – I was again enjoying my car – super proud of myself that I had fixed the problem on my own. The euphoria lasted only but for a few days, when after a 20 minute drive, I shut off the engine, only to be greeted by the CEL and the RP message – I was pissed off. Figuring that the car drove fine for several hundred miles, before the codes returned, I was certain that the issue was with the MAF sensor and immediately ordered a rebuilt unit from Parts Geek. A week later the refurbished unit arrived. My original MAF sensor looked brand new compared to the unit which was sent to me, but I figured that it’s not how it looks, but how it works, and promptly replaced the part and erased the codes. After a few miles of driving, the lights came back. I was ready to take the car to the dealer, but knowing that the sum of the parts for our cars is worth at least 10 times more than the car itself, I opted to go back to the forum in hopes of finding the real issue. The Refurbished MAF was sent back to Parts Geek.
The next item on list of potential problems was the fuel filter. With over 80K miles on the odometer and not quite sure when the last time fuel filter was replaced, I went to an Indy to have that service done. The original filter looked very clean and was not clogged at all. But since the car was already on the lift, I opted to go through with the replacement. It did not take long after that procedure and the erasing of the codes, for the RP message to come back – I was genuinely upset. Selling the car crossed my mind more than once – such blasphemous thoughts. I was ready to take the car to the dealer, knowing that they’d be swapping new parts by process of elimination – it would be expensive.
I have read several threads on the forum that sometimes the K & N filter let’s through too much air to cause the lean condition. I had nothing to lose, so I ordered a regular air filter on the net. Opening up the Air Intake cover, I removed the filter. Having the filter out of the housing, I took a good look in that chamber, not really knowing what I was looking for. However, I did notice something odd, something I have not seen before. Right behind the passenger side headlight, where the air intake housing sits, there is a valve of some type that opens and closes by a solenoid (I took a few pictures of it). There is also a spring fitted in such an arrangement, so as when the solenoid retracts, the spring is supposed to close the flap of the valve. Upon closer examination, I realized that the spring was set in a wrong position or rather it was loose and not returning the flap to a closed position. That’s when the light bulb went off in my head. I was certain that this was the root cause of the engine running lean. After a few minutes of fiddling with the spring, I returned it to its proper placement and placed the new filter in the housing. Codes erased again, ready to drive and see if the problem is fixed for good.
A week has passed and several hundred miles later, the codes are NOT coming back. The thought that I considered selling a beautiful automobile just a few weeks back, now seems preposterous. I wonder what would happen if I had taken the car to the dealer. Would they be honest and tell me that the problem was a part which costs a quarter, or would they fill the engine bay with thousands worth of new shiny parts. Gladly I will never know.

 

The flap opens when you put your foot down to let more air in. The intake snorkel is engineered to be quiet but is somewhat of a restriction at large throttle opening and RPM.

That said, that flap is before the MAF, so should have no effect on lean or rich conditions. There are even forum members who have removed it entirely to let more air in, and they have not reported issues.

I hope that your problem is gone, but am skeptical that flap could really be the cause.

 

Maybe the K&N was not exactly fitting right or messes with air flow a little. No-one seems to regret removing a K&N on an S-Type and there's no measurable change in HP (but still some claims that the HP gain is there even though unmeasurable.)

BTW, no need to let these cars "warm up" like that. Waste of fuel.

 

I've always been wary of the K&N air filter set-up. I believe that introducing oil into the airflow system with all of its highly-sensitive and costly electronics is simply too much of a risk to take. Good luck with your issue and I hope you indeed fixed it. Keep us posted....

 

Ditto on the K&N nix. All I had to read was that "they even filter better as they get dirty". Well, how well do they filter when CLEAN then? I keep my cars for many years (Kitty is over 150K), so I avoid anything that could reduce engine life - including the K&Ns.

However, getting back to topic at hand, I too don't understand why either the stuck flap or the filter could cause the lean CELs being as they're upstream from the MAF.

 

OK, maybe I'm missing something. I am not a mechanical engineer, but common sense dictates that air first enters through the AIR INTAKE housing, before proceeding on to the engine via the MAF sensor. I recently learned that there are two passages through which air enters the housing (before, I thought there was only one), before it passes the MAF sensor - the fixed opening above the wheel well and the dynamic opening - controlled by the solenoid and the spring (I took pics of the latter - see 1st thread). I am convinced (thank you for explaining Charlie) that in the “Sport” setting, the solenoid opens up the valve to allow more air to the engine. However, without the little spring in place, the valve stays open – thus allowing a higher volume of air to pass through MAF, than the ECU allows during the idle or low RPM driving. When this happens, the Check engine light and the Restricted Performance message is triggered by the computer.
If there are any daring souls out there (I wouldn’t do it), Place something in that valve to leave it in the open position, turn the “Sport” setting on, drive on the freeway for a few miles and see what happens.
As for me, it has been about two weeks since I’ve seen those darn dash lights.

 

Looking at the JTIS it appears this is a SC only setup, also on later models my 02 doesn't have this. Note sure what triggers it but if the spring was missing sure enough that'd be a issue..

 

The way to think about this is that the engine is sucking the air in, and the amount being sucked in is determined by the throttle body.


At low to medium engine speeds the existing opening on the air filter does not pose a restriction but at high load and high engine speed it is restrictive like a second throttle, so they added a second hatch on the air filter box to remove the restriction.


Now you may say why didn't they just make the existing opening larger and leave it at that, well I don't know but as was previously suggested, it was to do with noise reduction.

 

May well also be to help get smoother air flow at low speeds and that will measure better at the MAF which in turn will mean better fuelling and longer-lived cats.

Also, sucking the extra air from the engine bay will mean warmer air and you don't want that, especially at slow speeds. At high speeds you have little option short of doing as they do on e.g. XFR and have twin inlets.

 

Today the engine light and the RP message came back. Same deal as before. I made a short stop, restarted the engine after about 15 mins - the Sport setting was on... One minute later the CEL and RP come back. It was too late in the day for me to start taking stuff apart, but come Saturday morning, I am getting right to it.
Bummer... I was so happy when I thought it was fixed. Now back to the drawing board.

 

You can save a lot of time and money by using a scanner or better yet a blue tooth OBD reader and the Torque app so you can read short-term and long term fuel trims. While watching the STFT's at idle spray MAF cleaner around every part of the intake, supercharger hoses,throttle body, and EGR valve and watch for any change in the readings.


You will see instantly if you have an air leak. From you posts I really think you do

 

It seems there may be a pattern where you drive the car and it is fine, then shut it off and after a short sit you start it and get the RP again, and if you keep driving, a short time later the RP goes away. If this is indeed the pattern, you could possibly have a sensor or something that is malfunctioning when heat soaked. I can't really help beyond offering that thought, but I know that electronic components values can change with temperature, and if there is a component nearing end of life it could possibly do this. Just a thought. That probably won't help diagnose anything though. I agree with a previous post that you need monitor real time data.

 

You could also have a pinhole air leak in a hose that opens up when the engine bay gets up to operating temperature, then closes (and stays closed) when the temperature cools back down and the hose contracts....

 

Might even be a failing battery.

 

The thought that I considered selling a beautiful automobile just a few weeks back, now seems preposterous. I wonder what would happen if I had taken the car to the dealer. Would they be honest and tell me that the problem was a part which costs a quarter, or would they fill the engine bay with thousands worth of new shiny parts. Gladly I will never know.[/QUOTE]


DevSpider your tale of woe and ultimately redemption illustrates perfectly something I was told when I was a young boy by a mechanic I knew and respected. Always start your trouble shooting with the least expensive possibility and work up from there.


In my travails with both my '04 XJ8 and '99 XK8 I have been fortunate in that so far each of my fault codes that sometimes resemble the car playing game of Whack-a-mole with me have been caused by the relatively minor tweak or inexpensive part from a good MAF cleaning to the replacement of a dying coil.


As an aside I've used K&N's for years in everything from Fiats to Ferrari's without every having an engine problem related to air intake or other induction caused breakdowns.

 

My suspicion is confirmed. After opening up the air intake box, I see that the little spring got dislocated, thus not allowing the flap to close. At this point I am certain that the 2nd opening not being able to close is throwing the codes and the RF message. I wonder if there are forum members here with similar year car as mine who are willing to conduct an experiment. There is no need to open the air filter housing. The flap is accessible from behind the headlamp. If someone was to wedge something in there to prevent it from closing and drive like this for a few miles, I bet the engine light will come up.

 

Yes, that would be very interesting. Don't see why it would have to be the 2005. If it gets out of the 40's today and the wife is not looking at another car I'll try it. I guess the 2001 has the flap.
Side note, looking at a '72 Volvo P1800, no court would convict me!!!LOL
Wayne

 

A very iconic car, Wayne, but you must be a glutton for punishment if you decide to bring that puppy into your doghouse....

 

I am pretty sure the flap is something that started with the 4.2L in 2003. I'd do the experiment, but the stock air box is long gone.

 

It's not on my 02 xkr, I believe he's right which leads me to a bit of thinking.
If like some replace the air box with a KN the air volume probably changes some from stock (isn't that the point) and these folks don't see the restricted perf due to this. You might consider forcing it closed all the time and take a drive and see what happens.