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Originally Posted by red01
My 92 Old Achieve lopes while its in park, and only in park when above 150 degrees. It revs to 1000 rpm then drops below 500 rpm and repeats. Once in gear (neutral included), it runs fine. The computer is not kicking out a code. I've had the idle motor replaced. It's not the mass airflow intake censor, ignition wires or plugs, or a neutral safety switch as one mechanic made me believe. Any ideas?
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I am 90% sure that I know exactly what is causing your problem, and only because ive had the same thing happen to my on my 91 honda prelude and also a while back on my dads 96 buick century, etc... so i guess if you really hate bad news... then dont finish reading this post, lmao. anyway the bad news is that most likely its your intake manifold gasket. What i believe is probably happening is that your gasket developed a slightly leaky spot in it, so when the engine warms up to 150 degrees, the metal parts attached to the motor such as the intake manifold and exhaust manifold etc all start doing what metal likes to do when it begins to get heated up -- it expands. not nearly enough for the naked human eye to probably see the difference, but it does expand nonetheless. so... when the intake manifold starts getting warm, it starts to expand a little bit, which makes it try to pull slightly away from the head, which is the purpose of the gasket, its sposed to keep that airtight seal between the manifold and the cylender head even when it starts to expand, so that there wont be these kinds of problems. only problem is that your gasket has a thin spot or something like that where its not able to completely seal as it should in some spot on it... so as it expands it lets even just a little extra air get sucked in through that gap, which in turn causes your motor to start surging, or "loping" as you called it. my prelude is doing the exact same thing right now, although we have pinpointed that problem to probably be due to an air pocket in the cooling system and such... but anytime a motor starts to surge like that its usually due to too much air getting into the motor. the best way i've found to actually test this theory for sure is to take a can of flammable spray lubricant, such as WD-40 or something like that, and with the engine running (make sure you let it warm up til it starts surging first) and start spraying WD-40 all over the intake manifold where it meets with the cylender head, all around it in the gasket area, and if you suddenly hear the engine sorta change pitch or rev a little higher at some point, then you know you've found the leak in the intake gasket. at this point you would obviously replace the gasket, and problem fixed. i wish you the best of luck, and hope it helps ya! if i end up being completely wrong please let me know so i can shut up, lol. peace!
mike
03-23-2005, 03:55 PM
