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1991 Legacy Wagon Idle/Surge Problem - especially in gear

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Another subie newbie here - I have a recently acquired 1991 Legacy Wagon 2WD AT, with MPFI; 161k miles. While I've had the car, the engine purs like a kitten, albeit a rather large one. After replacing the spark plugs (just routine maintenance, right?), I have an idle surge at ~700-1100k, until I put it in drive which causes the surge to go wider in range and lower ~250-1000k. Even putting it back in neutral or park does not seem to change the surging. It goes from just about stalling out to slightly revved up, then back again. Cycle is about 1.5 - 2 seconds. This surge gets so bad that it literally rocks the car! The surge does not appear to go away with increased rpm's or while driving, just less noticable. No apparent loss of power.


Pulled all the plugs again, they look fine and are gapped correctly. All the wires seem fine, and pulling any given one seems to decrease the performance of the engine more or less evenly between all 4. I can't find any problems with the vacuum line system (no obvious disconnected hoses, cracked hoses, etc.). I do note, however, that the exhaust smells strongly of gasoline vapor, as if the combustion chamber is too enriched (too much throttle?) - it is noticable even up even by the driver side door.


I have not had any check engine lights, nor has the car had any history of overheating, etc.


Any suggestions on things to look for?

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The cycling you have could be due to the IAC being dirty. It controls the air flow at idle and I think is the thing that causes the cycling. Even when my car ran good it cycled in that manner.


I have a similar issue now and do not have a CEL. I am hoping it is the ignition coil. I think your rich smelling exhaust may be because the cylinder is not firing and just dumping a cylinder of raw fuel into the exhaust.


I think the surge (does it lurch forward when stopped because of a burst of power and you need to apply the brake more?) is from the car not firing on all cylinders all the time and then firing thus giving more power and lurching.



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Well, I finally solved it. After pulling the plugs out for the third time, I noticed that one looked a little funny as I was getting ready to put it back in - turns out the insulator was loose and when the plug is held terminal up (as it would go into the engine) and shaken, the insulator would slide down and cover the gap. If you held it sparking end up (the normal way to look at it??), the insulator slid back and it looked just fine, so now I know why I missed it. Just glad I didn't start gutting too many of the electronic sensors, etc, in the search for the problem. These were brand-new platinum plugs - obviously this says something about quality control, doesn't it?

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