1998 S70: Throbbing transmission in stall, low gas mileage

Gazoogleheimer · Post by **Gazoogleheimer** » 04 Nov 2009, 07:17

Wondering if it's time for an ATF flush.

I have a '98 S70 with only 69k miles on it. I have replaced the upper and front engine mounts to try and alleviate a problem I have been having at stop lights. When I brake and leave it in drive, the torque converter in "stall" mode. From the engine compartment, it seems, there will start to be loud resonances/vibrations which despite being harmless are rather annoying. It is like a very low frequency throbbing that sometimes is louder and sometimes is softer. However, this throbbing (not quick throbbing, but very slow) sound goes away of the transmission is shifted into neutral (or park.) The sound goes away when the car is in motion.

My ATF is a yellowish-slightly brown color, however does not have a burnt smell at all and smells quite ATF-y.

I'm getting only 14.5-15 MPG (no trip computer, fillup averaging) city and was wondering if that was a sign of anything (something I would really like to improve.)

Any ideas?
Thanks.

(Note: when I'm referring to "stall", I do not mean the car is stalling--I'm referring to "stall" in the torque converter where the engine speed is vastly higher than the transmission speed, which might be 0.)

FCPEURO · Post by **FCPEURO** » 04 Nov 2009, 12:42

I normally flush my transmission every 50K miles so if yours has not been done, I would do it.

Gazoogleheimer · Post by **Gazoogleheimer** » 04 Nov 2009, 19:07

Could bad/old ATF really make it vibrate significantly more?

bigfinn · Post by **bigfinn** » 04 Nov 2009, 20:32

Your vibrations probably have more to do with worn engine mounts. Replace with original volvo mounts if you want to quiet the vibrations. Upper engine mount, lower engine mount, and sub-frame mounts if they are original.. Replacing the upper engine mount with the poly mount will give you vibration no matter what you do, but is quite easy to do. You decide.

As for you ATF, it should be PINK!!!!! Do a full flush, or a modified flush with multiple drain and fills. Easy to do.

As for lousy gas mileage, it can be a combination of things. Do a stage 0 tune-up. Make sure your wheels roll freely without interference from a sticky brake caliper. Clean your throttle body. Add a good fuel injector cleaner to your gas for the next few fill-ups. Make sure your wheels are in alignment.

You have much to learn...but the good news is that you will find all your answers here at this site....just start searching and you will find yourself working on a car like you never have before. Good luck.

Post by **polskamafia mjl** » 04 Nov 2009, 20:37

What do you suggest is a good fuel injecotr cleaner? I've been thinking about using some just to see if anything will change. I get 33mpg highway so I'm not really looking to improve anything, more along the lines of preventative maintenance. lol

Post by **jblackburn** » 04 Nov 2009, 21:24

I know this sounds like a dumb question, but have you changed your spark plugs recently?! Were they gapped to .028"?! That's the biggest contributor I can think of to explain rough idle & horrible gas mileage...I'm not very erm...conservative with mine, and still manage ~20 mpg around town.

Post by **jblackburn** » 04 Nov 2009, 21:26

What do you suggest is a good fuel injecotr cleaner?

Put some Seafoam in the gas tank...it helps a lot more than any of the "fuel injector cleaners" do.

9394volvo850s · Post by **9394volvo850s** » 04 Nov 2009, 22:07

I would change the tranny fluid as preventitave matience but should be non related to your vibrations. what RPMs does the car Idle at?

Gazoogleheimer · Post by **Gazoogleheimer** » 05 Nov 2009, 08:40

The car idles at around 950 with the A/C on (if I recall correctly, I should check.) I'm planning on checking the plugs this weekend--and will replace with Volvo OEM if they are worn (which, if I recall correctly, one does not gap.)

The upper poly (mine was silicone) mount did not add any extra vibration, and actually alleviated some (however, I do know the difference between OEM and silicone)...could it be the transmission mounts? (which I don't know if I can really confidently replace myself.)

On stuck brake calipers: My front wheels do not rotate completely freely and when I was working on trying to replace a CV boot I could not get the caliper to come off the rotor (as the rotor was slightly worn and the pad was stuck on the "lip" on the rotor. I now know to "pry" between the rotor and brake pad to force it back--is this correct? Or do I have stuck rotors?)

The important thing, however, is that it isn't exactly "rough idle", it's rough idle under the load of the torque converter. (And not really 'rough', it only chokes or wallows occasionally--by occasionally I mean perhaps once in ten stops) but...I'll check the plugs. Easy fix.

Gazoogleheimer · Post by **Gazoogleheimer** » 08 Nov 2009, 09:37

Any other ideas?