Hi, very newbie to fixing vacuum leaks questions. I'm mostly used to working on old Jeeps without lots of lines.

Months ago, after replacing the front drive shaft & transmission, everything was fine, but about 500 miles later, I did my first off-road trip in the DiscoII and also changed the air filter at the same time. Threw the first P0174 and P0171 codes at that time. Nothing felt off on the rig at all, drove perfectly. If I reset the codes, they would come back somewhere between 150 - 300 miles of driving.

Finally starting to get some more evidence of a problem, so trying to dive in and fix it. Now there is a bit of a hesitation at times during idle @750 rpm, and it seems like MPG might have taken a small hit the last two fill ups. Also throwing more codes now. Just clicked over 89K miles, and no problems at all with my foot in it or power, etc. Everything seems to run fine still, except for the minor stumble at idle.
One other thing, it seems like it's revving up even higher at the first cold start in the morning - say, 2000 RPM or more, which seems higher than it used to. It only ever does that once, at the morning cold start.

I'm mentally ready to bite the bullet on the $ for a new MAF and all 4 new O2 sensors if necessary, because they could all easily need replaced.

However, I got to reading all the posts on here for the codes, and seems like vacuum leaks can be a lot of this as well. I followed the advice of some threads and bought some engine starting fluid, sprayed it on all places I could think of and listened to the idle change RPM. I will try to add the photos in a reply to this and circle the areas in red where the RPM changed. Do you think this could be enough to throw the codes? Or should I go ahead with the O2 and MAF sensor replacements as well?
Thank you for any help!

Fault log report generated by Torque for Android
=================================================

Vehicle VIN: SALTY16403A824805
Vehicle Manufacturer: Rover
Vehicle Calibration ID: Not present

Current Fault Log
------------------
P0171: System too Lean (Bank 1)
P0174: System too Lean (Bank 2)
P0300: Random/Multiple Cylinder Misfire Detected
P0303: Cylinder 3 Misfire Detected
P0304: Cylinder 4 Misfire Detected
P0305: Cylinder 5 Misfire Detected
P0307: Cylinder 7 Misfire Detected
P0308: Cylinder 8 Misfire Detected
P1171: [Chrysler] Fuel System Lean During Acceleration
[Hyundai] Electronic Throttle System Open
[Dodge] Fuel System Lean During Acceleration
[Jeep] Fuel System Lean During Acceleration
[Seat/Audi/Volkswagen] Throttle Actuation Potentiometer Sign.2 Range/Performance
[Volvo] Long-term fuel trim, Upper Limit

P1174: [BMW] Fuel Trim Adaptation Additve Bank 1 Malfunction
[Hyundai] Electronic Throttle System #1 Close Malfunction
[Seat/Audi/Volkswagen] Fuel Trim, Bank 1 Different injection times
[Volvo] Long-term fuel trim, Upper Limit

P1300: [Chrysler] Ignitor Circuit
[Honda] Multiple Cylinder Misfire Detected
[Toyota] Igniter Circuit Fault (Bank #1)
[Lexus] Igniter Circuit Malfunction (Bank 1 Or No. 1)
[Mitsubishi] Ignition Timing Adjustment circuit.
[Dodge] Ignitor Circuit
[Jeep] Ignitor Circuit
[Seat/Audi/Volkswagen] Misfire detected Reason: Fuel level too low

 

I thought this was an electrical piece, but it changes the RPM if starting fluid is sprayed on it.





Any idea what is under there that would change the RPM when sprayed? It's the open space behind the alternator, and under the hoses/cables.





Can anyone please tell me the name of this hose? It seems to change the RPM if I spray the fluid at either end. Would like to replace the hose, just not sure what it's called.






This one is kind of puzzling to me as well - this is a bundle of electrical wires inside the split loom, right? But, if I spray it, the RPM definitely goes up. Is there maybe something underneath or behind the wires there that is a common culprit for a leak?

Thank you all very much for any help with diagnosing this!

 

If I were you I would not start throwing parts at it. Find the vacuum leak or leaks and address that.

A friend of mine had an 04 a while back and he threw all kinds of parts at it trying to solve the P1171 and P1174 codes. He eventually sold the truck before figuring out the problem but after that based on things I read on this forum I became reasonably convinced that the problem was the fuel injector O-rings. It's too improbable that both upstream O2 sensors went bad at the same time. And yes, a vacuum leak that triggers the P1171 and P1174 codes can trigger the misfires.

 

OK, Thanks! I'll try to figure out where those leaks are coming from. By any chance do you know the name of that hose I have circled both ends in red? I'd like to order a new one. Not sure what to think about those electrical areas, but there must be a hose in or around those areas too...have to dig into it when I have some time in the daylight.

 

The first pic was your evap purge valve, the second between the alternator and a/c compressor is you coolant temp sensor, the third off the manifold going to the rocker cover is your breather tube that has an oil seperator in the valve cove and the wiring loom has no vacuum lines that I know of. Just the coil pack. The only conclusion I could think of would be the secondary air injection being loose somewhere and and it being like shooting ether into a carb. But that's just my 2 cents worth. There are more vacuum lines with secondary air

 

The breather hose that connects the Bank 2 valve cover to the intake fits on a plastic fitting at the intake end. You might check to see if the fitting is cracked or broken. If it is you can replace it for a few bucks with a brass version available in the plumbing section at your local Lowe's, Home Depot, etc.

Again, if you can't find a significant leak at any of the vacuum fittings it might be injector O-rings. Unfortunately it looks difficult to impossible to test them for leaks by spraying starting fluid since they sit under the upper intake and access is mostly blocked by the alternator and A/C compressor.