I have a 93-940 that has a rythmic noise from the engine. I can hear very clearly through the Air Box and with a piece of vacuum hose placed on the throttle body vacuum ports for the evaporator. Does anyone have any ideas? It is coming from somewhere in the engine. It is not from the alternator, a/c compressor, power steering pump, etc... It does not increase with rpm's.

Also, my exhaust manifold gaskets are leaking. Would that cause a poor idle?

Thanks...

Not sure of your noise, maybe more detail on describing it. Is it apparent only when the vehicle is stopped? Moving? Both? Pitch (high whine/low thrumb)?

Exh manifold gasket leaks can definitely affect performance, believe it or not, ambient air will be sucked in through the leak and the resulting increase in O2 content will throw off the O2 sensor reading making the computer think there is a lean mixture. It isn't a hard repair, just time-consuming, parts are cheap, just soak the manifold nuts & turbo/exhaust downpipe bolts in PB Blaster or some such penetrant so they come off easily w/o breaking the studs.

There is a section on Exh. man. gskt replacement in the FAQ's

http://www.brickboard.com/FAQ/700-900/EngineTurbo.htm#ExhaustManifoldGasketandStuds


'94 945T (daughter co-opted it for college, used to be mine)
'99 S80 (mom-in-law's)
'88 240DL (son's)
'84 242Ti (future commuter)
'89 560SL (wifemobile)
'88 300TE (my commuter, for sale)
'68 GT500KR (under restoration)
--
Bob K

Bob,

I do not know if the noise is present when moving, but I think so. It is a low pitch "whump-whump" sound. It is not extremely loud, but you can hear it. With the vacuum hose to the ports I mentioned it is very pronounced. ****When I increase the rpm's as I am listening to the throttle body, the noise ceases with rpm's and returns as the idle resumes...

Thanks for exhaust manifold info. I have checked out the FAQ area on it.

Don

I have the same car with the same noise. I can't figure out its origin. The noise I hear in my car is somewhere high pitch. It starts after the engine has wormed up. It does not increase with rpm. Sometimes it disappears for a moment when coming to a stop and resumes after the car is idling normally. I would also like to solve this mystery, but I don't think that is anything that is going to brake down the engine at this time.