strange sound on my 3.2 help!!

[martiniqueln]

1989 911 3.2 186K on the clock


Under no load engine sounds strong , no hesitation or strange sounds . can run it up in the garage and sounds great .
My problem is under driving conditions there is a sound similar to bogging down on the left side . Almost like it is a exhaust leak .
But the sound does not start until warm . Alittle bit of a howling sound when I drive next to a barrier.
any ideas will be much appreciated Sounds like a engine that is starving for air intake .

[ZOA NOM]

The howling sounds like a bearing. I noticed a howl on one side while taking turn 2 at Thunderhill, and I've ordered new bearings. As for the bogging, I would suspect a vacuum leak somewhere that may not be loose enough to show up without the load. Does the car idle normally? Does the idle drop if you remove the oil cap? If not, there could be a vacuum leak somewhere. The usual suspects are the manifold to head connections, and the many hoses found around the back of the motor.

[martiniqueln]

Thanks ,
car does idle normal
How many rpms should drop without the oil cap off ?

[martiniqueln]

If I have a vacuum leak will it always result in some power loss ?

[ZOA NOM]

The idle should drop a few hundred RPM's with the cap removed. A vacuum leak could be elusive. It could only show itself under load, when you accellerate, because f the increase in vacuum that results. The engine is simply an air pump. If there is a leak anywhere, it's ability to move the air efficiently suffers. You can spray small amounts of carb cleaner around suspect leak locations to detect a leak. The RPMs will rise if you spray the carb cleaner on a leaky location since it changes the air/fuel mixture when it enters unmetered.