It seems like restricted performance only comes on while idling. By rough start I mean it takes an additional second to start from cold when turning the key. Doesn't start strong like a Jag should. What I've done:

1. Air inlett pipe from throttle body to mafs/air filter had cracks in the bellows and was replaced with one without silencers.

2. Part load breather connector tab was cracked, don't think this was causing it but I replaced it anyway cause the tab was broken.

3. New air filter, replaced hadn't been done in awhile.

4. Cleaned MAFS. Should I replace it?

What should I try next?

2000 Jaguar XKR

Any codes pulled? Sometimes hard starts can be the fuel filter. I would look for codes first.

Only code is p0174. I have a replacement fuel filter I could put on but does that have any relation to the code?

Since it's only B bank it's hard to say fuel filter or fuel pump, but that is possible. If you were able to read fuel trims that would help. Even the upstream oxygen sensor could be a cause.

Replaced fuel filter and cleared code. It probably needed to be done but I still have the same issue.

Any reccomendations on fuel trim reading tools? I don't mind buying one if it will help me figure this thing out.

Should I replace the oxygen sensor....

Pre-computer controlled vehicle troubleshooting..... you may have a vacuum leak. Are there any vacuum lines that are hanging free after you played with those parts? Also, is there any weird sucking sounds anywhere that weren't there before? Another... old timers like me used to spray the engine bay with starting fluid (ether) and if the idle increases when you spray a certain area, that's where the vacuum leak is. Just an idea is all.

A $5 elm327 can usually read fuel trims.

I used to get p0174 in my supercharged range rover. A can of Gumout's Best Fuel System cleaner, always fixed it -- for a six months or so.

Lately been using Sea Foam in my X308 which keeps the injectors spraying cleanly.

Have you cleaned the throttle bore and plate?

UPDATE: Yesterday I had a couple of times where I would try to start the vehicle and unless it was given some gas it would cut out. The restricted performance message seems to only come on when the vehicle is hot and idling. If I do 3 short trips, letting it cool off inbetween I won't see a restricted performance message and the check engine light will go off by itself.

There might be a light sucking sound in the engine bay but it is hard to tell with the noise of the engine. I tried the old school starting fluid trick with not much luck. What should I spray? Don't want to miss anything... Is there any possible way to rig up a smoke test with one of those Halloween smoke machines?

There seems to be a lot of different options for the elm327 "http://www.amazon.com/s/ref=nb_sb_noss/187-0649122-6773358?url=search-alias%3Dautomotive&field-keywords=elm327". I'm leaning towards the $24 BAFX product as it gets the best reviews but it doesn't say elm327 anywhere on the product page so will it work? There is also the super cheap mini elm327 listed on that page for $6.31 but it gets pretty bad reviews. I want something that will last awhile... Do you have one? Which one did you get?

I bought a bottle of gumout but the directions say to use it when the tank is almost empty and you are about to refill. Should I listen to the directions? Unfortunately I have almost a fuel tank so it will take a few days before I can use it if I follow the directions... Yes I cleaned the throttle bore and plate.

If you can force smoke into the intake tube where it connects to the air filter and hold the throttle butterfly open that should do it. Oh, and block the full load breather tube.

I made a smoke tester using plumbers smoke test pellets, copying a design I saw here somewhere. They used a cigarette I think.
I put a bicycle valve into one the end of a piece of plastic tube, the other end of the tube I hot glued into the lid of a large airtight container. The valve you can connect to a hand or electric pump - hand is quite good because you can control the flow quite well.
I hot glued another outlet tube into the lid as well, and the other end of the tube into an old tuna can, which is just the right size for the intake.
inside the airtight container I put the smoke pellet on a piece of metal so it wouldn't burn through the bottom.
If you undo the (engine) intake tube where it meets the airbox you can get a good seal between can and intake.
Light up the smoke pellet, seal the container, and start pumping. no need to hold the throttle open, that stuff finds its way through any gaps it can find.
After I sealed up the full load breather (leaking like a sieve) it took me three or four pellets to find the next source smoke - it turned out to be the part load breather.

Thanks guys for the information on doing on a smoke test. I appreciate it! Wish there was a video but I'll figure it out when I have time.

I'm now getting codes for both banks p0174 and p0171 I believe they are. Still only seems to happen when idling and after reaching operating temperature.

I think I fixed the start then cut out problem, looks like one of the radiator fan connectors was a little lose also causing the fan to stay on for a few minutes after the car was turned off. It still has a little trouble starting when cold but not near as bad.

there is a video somewhere, not of mine but I think it was RaceDiagnostics.
Make sure you don't get a bluetooth elm37 if you have an iphone, you will need a wifi one. For android bluetooth is fine.
My (wifi) one looks like this:
that is, with the blue/orange label.

When I saw how much my full load breather was leaking (at the intake connector) I bought a new one, and it leaked just as bad. Might be worth putting a thicker o-ring on there and/or some tape, see if that helps.

Otherwise, I'd get smoke testing. Since you have it on both sides I'd guess it'll be something on or before the throttle body.

Just spraying the mafs is not enough. Clean it carefully with q-tips and pipe cleaners.

Cleaning the MAFS with the proper cleaner is! Do not scrape or scratch the sensor and. What ever you do do not touch with your hands.

Gus
www.jagrepair.com

I had a about the same problem a few years ago. I had to use a scan tool that read live data and watched the fuel trims as I sprayed around the intake. once the leak was found, the fuel trims went negative. My leak turned out to be the o ring seal where the intake elbow joined the composite intake. Remember, at idle the throttle valve is near closed, causing intake vacuum inside the intake to be greatest... so it's more likely to be a problem at idle. Looking back, I believe if not for the live data, I may still be looking for it. Keep us posted!

See pictures... I think this should be sufficient for a smoke test (all stuff I had around the garage), if I remove the breather hose smoke does come out of it but unfortunately I haven't found a leak anywhere. I've never done this before, do I have it attached correctly?

It has been a little while sense I cleaned the MAFS, I think all I did was spray it with a can of MAFS cleaner, I did not touch it with my hands. Maybe I should try spraying and cleaning it with q-tips?

Thanks for the heads up about the iphone/android compatibility. I think I'm going to purchase this one instead of the elm327: . It says it reads fuel trims, works with Android, and gets great reviews.

It still struggles to start when cold, give it a lil gas and it starts right up.

Do not touch the mafs wires.

Don't touch the actual wires themselves or the contacts at the end of the wires? Here are some pictures of the wire that connects to the MAFS. The black wire on the right looks slightly pulled out more then the other wires, is that normal? It also looks really dirty, maybe I should try cleaning it?

I ordered the Bluetooth tool so I can read the fuel trims. Should be here no later then Friday!

I believe he meant the MAF probes, not the connector to the harness, that can be cleaned as any normal electrical connection though I do notice you have a long area of harness open. Wonder if it was ever changed