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Q: Low engine compression on 1999 Toyota 4Runner

1999 4 cylinder 4 Runner... With 239K on the original motor.. Well I just put a new exhaust manifold on it.. and its runs better.. had a mechanic check the compression and it was bad.. #1 cyl..90 #2 cyl 90, #3 cyl 100 and #4 cyl 175.. Now.. He is telling me that they should all be at 175, and that doing a valve job will only make it worse. It has never had a valve job with 239K on it.. I am willing to take a chance. He said that the engine will "fall apart".. So my question is.. should I do that valve job or just drop in a rebuilt engine??

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I would check the valve clearances first see if any valves are pre loaded (no clearance). Cylinder leakage test is a good test off an engine. Each cylinder is tested in turn at top dead center (valves closed) air pressure is put in each cylinder is checked to see how much air escapes. Air escaping can be traced to the inlet valves, exhaust valves, head gasket or piston rings.
Does your engine presently burn oil or have you religiously changed the engine oil and maintained your present engine? It hard to give advice without being able to see your engine and hear it run. Doing a valve job and getting it to seal properly will not do anything to help worn piston rings or a worn cylinder bore. Get another opinion and way up the pros and cons then.
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I've seen these engines with a lot higher mileage. Way up the costs of swapping out the engine and be wary of rebuilds quality of rebuilds differ. Is the rest of the truck in good order?
Thanks for the response... I have kept the engine well maintained.. oil changes and spark plugs when needed.. air filter.. all that.. hoses.. the engine idles rough.. well not really rough but a little... it does not burn oil.. i keep it real clean....So with that said... What do I do??

Thanks !!!
Yes.. the rest of the truck is in excellent condition... I drive alot on the highway.. so I just put new shocks, tires and brakes..
What did you end up doing with your 4runner? I have a 2000 4cyl with 124K that is having the same problem. I was basically told it needed to be re-built.
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