Weird sounds - NA 20V 850 - 1997

DennisCA · Post by **DennisCA** » 04 Dec 2025, 02:24

I've heard this a lot lately when it's gotten colder outside, it's a pretty low frequency, bass-like sound. You start the engine cold and let it run for about 20 seconds and then this sound starts. It goes away after maybe a minute or so.

Recorded a video this morning, at 0:23 the sound starts, you have to listen carefully to hear when it starts. It's more noticeable in person. Part of me wonders if it's the secondary air pump I am hearing.

I also have another sound that I can hear when the car is stationary and the engine is idling, doesn't seem to make any difference if the engine is warm or cold, it also starts up after a while. It's a "chugga-chugga-chugga" sounds. It can start now and then and stops after a while. I've thought this was the secondary air pump personally but it shouldn't start if the engine is warm.

I know the pump is broken, I've disabled it in the ECU by soldering a diode so the CE light won't light up. The rubber mounts are partially broken so it's a bit loose. I tried cutting the black grounding wire coming from it, figured that would prevent it starting. But it made no difference. I guess I could have removed the relay for it. Maybe that should be my next step in diagnosing this.

454cid · Post by **454cid** » 04 Dec 2025, 07:35

I could hear my air pump from the cabin. It sounded like a vacuum cleaner, until it quit. I would also see the lights slightly dim from the extra electrical load. This was often when the car was fully warm. I no longer buy into the idea that SAS is only used with a cold engine. Both my Volvo and Mercedes will turn it on at other times.

Post by **abscate** » 05 Dec 2025, 03:42

It should only come on at cold start. I don’t know if the code for the it is public but it’s a cold start feature only.

Once the car goes closed loop (5 minutes) it would seriously mess up fuel trims

DennisCA · Post by **DennisCA** » 05 Dec 2025, 05:04

Then I wonder what the chugga chugga sound is... as far as I can hear it's coming from where the SAS pump should be.

454cid · Post by **454cid** » 05 Dec 2025, 12:04

DennisCA wrote: ↑05 Dec 2025, 05:04 Then I wonder what the chugga chugga sound is... as far as I can hear it's coming from where the SAS pump should be.

Maybe the wheel is damaged? There's also a vacuum pump down there, I think....had to do with the cruise control.

Post by **matthew1** » 05 Dec 2025, 16:55

Based on timing I'd say air pump. That's pretty much when mine would activate after key turn.

If that is it, feel good that it doesn't sound like mine did: hyenas on Xanax howling at me from the other end of a 4-mile long tunnel.

DennisCA · Post by **DennisCA** » 05 Dec 2025, 23:57

454cid wrote: ↑05 Dec 2025, 12:04 Maybe the wheel is damaged? There's also a vacuum pump down there, I think....had to do with the cruise control.

It does remind me of a vacuum pump now you mention it. Would a car without cruise control have it though?

With wheel, you mean the cars wheels, I don't think so because I only ever hear it when the car is standing still and I am idling.

454cid · Post by **454cid** » 06 Dec 2025, 10:15

DennisCA wrote: ↑05 Dec 2025, 23:57
454cid wrote: ↑05 Dec 2025, 12:04 Maybe the wheel is damaged? There's also a vacuum pump down there, I think....had to do with the cruise control.
It does remind me of a vacuum pump now you mention it. Would a car without cruise control have it though?

I don't know. I was surprised to find the cruise needed a vacuum pump, given that gas engines create vacuum. I don't know what else it might be used for.

With wheel, you mean the cars wheels, I don't think so because I only ever hear it when the car is standing still and I am idling.

No, the blower wheel/blade/impeller inside the SAS air pump.

Post by **abscate** » 06 Dec 2025, 10:31

That’s it, cruise vacuum pump. Definitely have a look to see if there are two pump things under the battery area. You will also feel the one that is running