Engine braking into low rpm = shaky car
 

Hey all,

My 88 T2 has 100k miles. I have noticed lately that if I leave it in gear while decelerating and solely let the engine slow the car down, it'll be all fine and good until I hit about 2000-1700 rpm. Then it hits some magic frequency and the car and engine start shaking forward and backward pretty badly, almost in opposition to each other, so its not pleasant. No strange sounds though. It doesn't happen often because engine braking into that low of rpms is pointless, but I don't like it. Is it likely that my motor mounts need replacement? Is this normal?

Thanks for your help.

if it helps at all my '92 FD hates being below 2k rpms. I have also read elsewhere this is cause by drive line slop in a manual car. For it to stop, normally, just press the clutch in let it back out slowly and give it some gas. For me i try to stay in a gear that will keep me above like 1800 rpms if im just creeping down the road.

adjust you TPS, my 88 N/A would do the same thing, adjusted the TPS to 1 volt, haven't had a problem since

I've had that happen twice, one was driveline slop from old mounts, one was maladjusted TPS. I say check both.

Thank you for the help! I’ll adjust TPS and check mounts and report back :)

Ok I adjusted TPS today, I was reading 1.4k ohms on the low end and 5.4k up top. So I adjusted the low end to 1.00k and it didn’t seem to make much difference.
The two lower engine mounts look like they are in pretty good shape. no cracking or anything.

In my post wrenching test drive I noticed that the shaking begins at 1500 rpm while engine braking and it lasts till about 1400 rpm and goes away. It's very brief.

You may also want to check out the trans mounts

I will go look. If they need replaced, do you recommend OEM or RB comp mounts or something stiffer? I saw Delrin mounts as well :eek:

if it's a street car, I would go with the RB comp mounts over stock. Delrin and aluminium mounts are pretty harsh

^^^^ What he said. I tried Delrin mounts on mine (which was my daily at the time) and it was unbearable for a road car. I went with polyurethane and I like it, but it still might be a little buzzy for your liking. My vote is for OEM if you want to retain the comfort of stock mounts.

thank you for the feedback!

*EDIT* I used the resistance method for adjusting the TPS which I found at this link: http://fc3spro.com/TECH/HOWTO/TPS/tps.html
I don't recommend doing that method -- it threw my adjustment WAY out. Instead, I used a voltage reading with the ignition switch ON. Car runs much better and the cold start sequence isn't goofed.

Car still shakes a little when engine braking at 1500rpm, but I suppose it is just old mounts. I found out my BAC valve is dead/clogged, I'm not sure if that has anything to do with it. I'll see as soon as I replace it.

It would be a good idea to replace the u-joints on the driveshaft, I had the exact same issue and it ended up being the u-joints. they are staked in tho. I had the lovely experience today of having the u-joints grenade on me and take out the rear end of my tranny along with it.