Strange noise/brake puls at idle

[Tom Dunn]

I and my 91 Legacy Wagon have sucessfully completed our move to NC from the Adirondacks. Car ran great, NO cooling issues, good MPG despite being heavily loaded, ect.(Now I need a job!)

Yesterday however, while idleing on the roadside getting the mail from the rural box, the car, from the engine compartment(?) made a distinct "whirling/buzzing" kind of noise, not unlike a small motor pulsing. It would go in 2 or 3 second bursts, and induced a distint pulse/vibration in the brake pedal. Car was in drive, foot on brake. The brakes seemed fine, however, going down the dirt road to the house. No noise I could hear either. Once I pulled in the driveway, it happed a second time while sitting there in "Drive". I went out to run some errands, and the problem occured several more times, always while stopped with my foot on the brake. Brake function seems fine, but I've not tried the anti-locks.

Ideas?

[Adnan]

Hi,

 

One thought is that the pulsing you feel is related to engine vacuum and/or current demand on the alternator at idle. Applying brakes turns on the brake lights, which in turn puts a load on the engine. I had that happen on my 1984 Corolla as a normal thing. I just got used to it after a while.

 

The other issue is related to vacuum. At idle you have very high manifold vacuum and it may be that the brake booster is leaking and therefore affecting the idle. The engine would be most sensitive to a vacuum leak in that state.

 

Hope that helps,

Adnan

[Tom Dunn]

I hate to sound like a dummy but......I know the source of the noise, but not sure what the unit actually is. It's a cast box, made by Bendix I believe, and part of the brake system. There are four steel lines connected to the top, and two on the side. It's in the very right front corner of the engine compartment, with a small solenoid on the side. Brake booster maybe? I've not yet named the part/function....but......

I've got my best people on it right now........

[SevenSisters]

It sounds like the ABS system. Several postings dealing with a bad ABS relay. Check that first.

 

Are you getting an ABS light? Could also be rust/metal debris on the tone rings making the ABS think it should turn on. Could be a bad wheel sensor too if the ABS light comes on.

[Tom Dunn]

Actually, over the last two weeks or so, I had the ABS light come on a couple times. No rhyme or reason, would just come on, stay for a hour or so until the car was turned off. It would take a couple days to return maybe. There is, however, no ABS light associated with this problem.

[Tom Dunn]

ABS indeed. The noise is the ABS pump cycling, so there is a problem, I'm guessing, with one of the wheel sensors. Four wheel ABS on this car (I believe). Since they are some kind of an emitter/pick-up arrangement, I'm hoping maybe I can clean them with some brake cleaner perhaps.

[unverviking]

I and my 91 Legacy Wagon have sucessfully completed our move to NC from the Adirondacks. Car ran great, NO cooling issues, good MPG despite being heavily loaded, ect.(Now I need a job!)

 

Glad to hear that you made it NC.. Now that you've left the wonderful berg of Inlet, it's warmed up and most of the snow is gone... (Don't know for sure, but it is in Roch)

 

Good luck to you in NC...

[SevenSisters]

Pick up a stainless steel "tooth" type brush at Lowes or Home Depot in the welding section. Clean out all the crap between the tone ring and sensor. Then clean off the rust scale off the tone ring.

 

One more thought. My ABS did s similar thing when the wheel bearing was going and the hub/sensor/tone ring would heat up. Fixing the bearing solved the problem.