1989 olds 98 3.8 litre surges LIKE HORSEY

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There is 300000 km on it.Compression is good,new battery,alternator,starter,
wires,plugs,.the car surges after 2500 to 3000 rpm.It is behaving like a rev limiter.It makes the car buck really bad. I first noticed this when i drove it a couple months ago.I WAS IN A HURRY ONE DAY AND REALLY DROVE IT HARD.My wife drove it and then she noticed it too,but it is showing up at a lower RPM.I have a new fuel filter ,but the old one might as well be welded on,it is so rusted it is sickening.if i rev it up with no load on it ,it will go to 5000 rpm easy.it will sit at 3500 steady.BUT when you drive it ,under load it is like it losing vacuum.my old 454 used to do that ,but the vacuum advance on the distributor was mechanical.I am thinking to do a scan on it ,2 months ago the service engine soon light came on,I unhooked the battery for 15 min,and problem gone.I was thinking of scanning it ,but many times have been mislead by that.There are some TSB out there for this car,but not for this problem.I know that the 3.8 can have intake manifold gasket problems.this one has a little oil leaking,and I swear I can hear a hissing under the hood near the back of the engine.I have to much of a busy schedule to play with thing. any ideas would be much appreciated.

posted by  the lobster

it was the catalytic converter.the hiss is the exhaust flange donut.the MAP sensor is expecting to see much more air flow when under load.that is what triggered the service light .since it does not produce the exhaust when it is not under load,it will rev fine,in park or neutral.i pulled the o2 sensor and the back pressure is way above the acceptible limits.i guess she will drive it another 300000 km now.

posted by  the lobster

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