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Discussion Starter · #1 ·
The car has 193,xxxmiles and no check engine light, no stored codes found. The car is a 2004 5mt forester xt. On a cold start the vehicle idles at 1.5k. It gruadually lowers to as it warms up. Once warm the vehicle is idling rough and rpms seems to be surging just a bit. Took the car to get looked at regarding the rough idle and since its so high milage and i wanted to know the general health of the car i asked for a compression test as well. The place i took it too specializes in subies and buggys with boxer motors.
Ok, so i got the results, first after searching for the source of the rough idle they were unable to locate any issues. Said they ran a smoke test and all the vaccum lines are good, no leaks, pvc system working and no oil build up anywhere or leaks. Said he was surprised for a car of its milage because all the rubber seems to be in real good shape considering the age. When taking it on a test drive said he felt the rough idle and noticed a misfire but when back at the shop couldnt find the source of the misfire as all coils and cylinders seemed to be firing normal plus no check engine light is present. Then went on give me the results of the compression test, 120-122 across the board. Said it was low but the vehicle runs well and drives well plus the numbers didnt wildy deviate from one another so it seems ok just old. He said the leak down test didnt point to any direction as there was a minimal loss of pressure and he contributed it to worn rings or possibly sticky valves. Mentioned again that its got some milage so considering its running strong and unless your looking to rebuild you can just drive it. It seems fine. It continued to tell me that they were unable to locate the misfire rough idle issue but suspected that possible fuel injectors.
I dont feel like ive actually learned anything useful about the car...

So ive done a bit of reading and from what i can gather the compression on these xts should be between 150 and 180? Im not even exactly sure pf the engine code for the motor. Im pretty new to the boxer motor.
Any body have any input on this motor and idea what could be cause a rough idle and missfire? Do these compression numbers seem too low? Should i invest into looking for the cause of the misfire or rebuild? Can i rebuild just the block? New pistons new rings new gasket same old head. I am really trying to get at least 1.5 more years of this motor in normal driving before having to rebuild the motor. Im currently strapped for big project money.

Thanks for reading it all. Sorry for any grammatical errors lol.
 

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G'day @Ish3600

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Discussion Starter · #3 ·
Access to pc is limited at thw moment. Mine is unplugged in a corner of the house.
Im from Long Beach California if this helps.
 

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compression is generally a function of either piston ring wear and sealing when warmed up, oil viscosity at the oil control and compression rings or head gaskets, with head gaskets it almost always shows which cylinder has bad HG as it will have lowered compression .......... since all 4 cylinders are showing 120 to 122 lbs.psi ,.......... then it is usually ring wear,................. you can show this by correctly testing, and then adding a spoonful of more viscous oil[ w 30 or w 40 something] to each cylinder as you test, to see if the compression goes up as the oil makes a more useful seal temporarily ,,,....,in more rare cases bad cam lobes can lower compression and worn valves/valve seals can cause lowered compression as they dont seal correctly....., any leak can lower compression ,................. there is no visual observation that can tell you if a coil or plug wire or plug is weaker, , ohm meters can help you test plugs and plug wires, and coil testers can tell you what volts are outgoing , if you are still using the priginal coils , wires or plugs , then change them, ........running .rough feeling may also be caused by bad motor mounts allowing the engine to shake a worn or broken cam lobe can cause rough firing, , but it would be weak or rough at all speeds,.............. bad sensors , can cause roughness , something as simple as clogged air filters also, or clogged catalytic converters or O2 sensors from bad turbo letting oil or debris into the cats./ O2 area ,
 

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2018 X3 M40i / 2016 X3 xDrive35i
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Fuel injectors sounds like a reasonable possibility. 120-122 is a little low, consistent with high mileage, but not likely to be the problem here. Did they clean the throttle body? MAF and MAP sensor cleaned?
 

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Discussion Starter · #6 · (Edited)
Thanks for the input guys. Ill ask the guy if he checked the throttle body,MAF and MAP and report back. Can i clean the throttle body myself? Like removing it and scrubing it down myself? MAF sensor cleaning difficult? Is this somethig i can do easily? My other vehicles have had AFM that didnt require cleaning so im not to sure how to do this.

Ill invest in spark plug wires, air filterand change the oil and look for debris like metal shards or what not. Guy did have a chance to check the plugs and said they all looked in great condition didnt show any bad signs, but would these things not cause a CEL to appear though? Like bad o2 censor or bad or going bad catalytic converter?

Topic of oil i know 5w40 or 10w40 is recommended but on a vehicle with 193k miles? Does anyone go 5w50 is this too thick? Last high milage vehicle i had was a ford bronco way back in the day and i used dino 20w50 on that thing but i cannot see this motor needing that thick of any oil.

Thanks again for the input guys.
 

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2018 X3 M40i / 2016 X3 xDrive35i
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All of this is fairly easy to do yourself. MAF and Map can just be pulled with a couple screws (be careful not to strip them!) and use MAF sensor cleaner found at auto parts store. Throttle body can be done after removing the intercooler. That's a bit more trouble just as you have to get the back on without pinching hoses.

And no worn spark plugs and inefficiencies in spark wouldn't necessarily throw a CEL.

Do not use 5w50, 5w40 would be a good match.
 
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