Check engine light is bugging me. 1 year ago i used to have check engine light come on but then after driving few km's it would automatically go off and it never came back on till last week I decided to take it to local mechanic and asked them to reset it for me. they've done it but the error codes were showing ( Cylinder misfire) ( System too lean) i don't have the exact codes.

a little pre-history of my xf:

During summer 2016 My cooling fan was running constantly after almost every time i cranked my engine. so I had my mechanic to diagnose it and they replaced coolant thermostat along with coolant reservoir since it was leaking badly.

I always have the tire pressure error coming back on but once i inflate tires it goes off for good while ( usually lasts 1 week). using technic suggested on this forum 25% deflate , ignite engine inflate back up 3 psi.


so as for check engine light, i had it reseted by mechanic 3 days ago and it came back again driving my car. Im not sure what i should do? my mechanic mentioned something about replacing spark plugs and ignition coil and few other things related to (cylinder misfire, system too lean...) but i dont want to be paying big bucks for something that is not necessary.

The only thing I can tell from my view is last week i had 1 issue which is basically whenever i start my engine , the engine ignites but then it turns right back off. the engine rpm drops from 1000 to 500 then to 0 after few seconds. the only way i could had engine running was by starting engine again right after putting my feet on throttle, give it some gas so engine doesn't turn off. but then this problem kind of got solved since last week friday. the only thing it still does is, engine cranks but rpm shakes, like the engine shakes on cold start for few 10 seconds or so then it goes back to normal.

Another thing i felt is wrong is my throttle response is a bit weak. for example when i'm on gear 3 its bit sluggish for engine thats 4.2 naturally aspirated. i have about 110K on my car. gear 2 is also pretty slow to fill the rpm. i feel my engine is becoming weaker and weaker everyday. im not sure how to make it run like first day. or at least have it tuned properly. ( are there any pulleys or belts that fit to 4.2 naturally aspirated to could fix this sluggish problem?)


I have always had my oil changed on-time running recommended oil (Castrol edge synthetic). had my battery replaced one year ago from dealer. maintained my vehicle always on time. changed my air filter last week to K&N, a little better but still is the same thing.


Im not sure what could be causing my check engine light. sluggish throttle response, engine stall right after starting my engine. if u guys suggest anything or had experienced my issue , suggestions would be appreciated.

I love my xf and i hope engine doesn't run wrong on me.




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What are the exact check engine light codes?

System lean/Misfire is most likely a vacuum leak. Have the shop diagnose and repair. A vacuum leak would cause hard starting and rough idle. The 09 SC is know for having vacuum leaks from a faulty plastic line back behind the supercharger.

A shop should be able to diagnose a lean condition related to a vacuum leak. I wouldn't throw random parts at it. Find the source of the leak and fix it.

 

@Blackcoog thanks for the tip , i'm gonna have my spark plugs replaced soon and ask the mechanic to check that vacuum leak and ask to have all the codes.

 

Does the 4.2 have a replaceable fuel filter?


If so, I would look replacing that. Low fuel pressure (due to clogged filter)could cause a lot of drivability/idle issues.

 

Blackcoog nailed it a shop should be able to pinpoint the issue from the codes. I wouldn't even replace the plugs if the "issue" is what you want to correct. You will replace the plugs and still be at square 1 with the check engine light and performance issues.

 

Read the codes and report back. Don't just throw parts at it. IMHO your mechanic is looking to you to fund their next family Disney trip. Time to fire the mechanic and find a competent one....

 

It does. It's located behind the plastic front fender liner, on the LH side of the car.