Hi Guys i am not exactly new to the forum but am new to this car.. I finally admitted defeat and sold the xk as soon as i had got it running correctly just too much work for me but now have another s type this time a v8 4.2 which i bought with a gearbox fault I have now fixed by replacing it but now the engine light keeps coming on and fault codes po171 and po174 keep coming up. I think it must be some kind of vacuum leak but dont know where to start looking. does anyone have any pics to guide me to the most likely places for this leak to show up? thanks in advance Ian

 

id start with the easy stuff , clean your MAF sensor , and both cam covers have breathers on them one is a pcv valve held down with two 8mm bolts check the o-rings under that . and each connection on the pipes have at least one o-ring at each end , also the dipstick o-ring is important , check the brake booster pipe connections as well .
it would be easiest to use an obd2 scanner tool to watch fuel trims as you spray starting fluid (ether) around the connections and watch for spiking trims .
speeds the process hugely . failing this you will need to check the throttle body gasket and intake manifold gaskets .

 

>id start with the easy stuff

Indeed, and don't forget to tighten the two bolts on the side of the shifter underneath (take the belly pan off, look up on the left side of the tranny and you will see two bolts on the side of the shifter).

They tend to loosen with time and if they fall out the car will be immobilized.
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Jaguar - it's not an automobile, it's a Motorcar
2015 JCNA National Slalom Champion Class M
Current: '08 S-Type 4.2 "Satin Edition" (250.06 whp / 259.67 torque)
Past: '05 X-Type 3.0/auto Jaguar Racing Green

 

What exactly did you replace?

 

Hi Mikey , I replaced the full gearbox as I have a donor car which I know the gearbox is good in as I have tested it fully but the engine in that is shot. The issue with this one came up as a gearbox fault and it kept coming up restricted performance when accelerating replacing the gearbox has fixed that issue but as I say it now has the engine management light on which will not stay off. When I clear it it is fine until the car judders then comes back on fault codes read po171 and po174 everytime. No more gearbox fault , rear wheel bearings and diff changed to at the same time and when I look at possible reasons it all seems to be pointing to an air leak somewhere but I dont know where to look

 

Don't clear the codes. Fix their cause.

Start by watching fuel trims - see the many many threads.

 

I have also noticed tonight that when the juddering happens the brake pedal seems to go very hard for a few seconds when i try to slow down to get the juddering to stop

 

Check the vacuum supply line to the brake booster for a leak.

 

Order a cheap ($50) MAF on line and replace yours. It's a simple job and I think will fix the problem. It could save lots and lots of hours hunting for a vacuum leak that may not exist.

 

thanks dougcthr but i have already tried that as i bought a couple for the donor car before i decided to buy this one instead and thought the maf may be the fault with that one so when these codes showed up i tried both a replacement and a genuine jag one but no change

 

thanks all for the advice.. all fixed now believe it or not it was simple with no signs of any blowing the exhaust to manifolds had come a bit loose retightened them and after a couple of trips all fault lights went out I attached the obd reader and read the same codes as before erased them and they have not reappeared. Now to try the supercharger on the donor car engine first