My 87 MT NA shudders/bounces/hops/etc when letting on or off the accelerator at low speeds. (Basically, engine torques through the car.) I also get a little surging when cruising at low speeds. The car is hard to launch or shift smoothing and slipping the clutch helps. The shuddering increases proportionally to speed the accelerator or clutch change. The problem entirely disappears at higher speeds.

I've already a done full tune up; replaced the clutch, driveshaft, motor mounts, tranny mounts, shocks, and springs; rebuilt clutch hydraulics; and adjusted the tps and clutch.

The car idles perfectly so I don't expect a vac leak and the diff mounts seem to be fine. (I may start replacing these since I’m out of other ideas.)

I've been working on this for a while and I’m out of ideas. What am I missing? Any suggestions?

 

Maybe it has something to do with the throttle position sensor (TPS). It sends signals to the ECU to smooth out sudden throttle changes. Another thing that might be worth looking into is the bypass air system in the throttle body. These are just guesses based on my understanding of the throttle system. See if you can get someone else to agree with me before you start poking around.

Maybe you are letting off the throttle at too low a speed for the gear you're in, so you are getting sudden engine braking....just kidding.

 

I have the same issue, I got my 7 like that, it's real shaky in low speeds when i let go of the gas. Any more help? Thanks.

 

TPS for sure. It either has bad spots, or is out of adjustment.

 

I agree that is sounds like a TPS problem, but TPS is perfect. I've reset it 3 times and it has not blowouts. I've also cleaned the BAC and it appears to work

 

When you set it, you set it when the car was warmed up, right? Just want to make sure.

 

Also, what RPM does it do this at? If it's below 1500 RPM my NA did that, too...

 

The car was warmed up when I set the TPS. It shudders under 2K RPM. It also shudders any time I get on or let off the accelerator.

I’m going to get in on a lift for another look at the diff this afternoon.

 

my car does that too

 

I think I remember mine doing that if I went WOT at a low RPM, but it never did it above 2500+ RPM. I know that for a fact. It's probably just cause these cars generate so little torque at the lower RPM range...

 

My 7 does the same thing when you let off the gas

 

They ALL do that, even with everything set perfect.

 

mine does that too.


it feels asif something in the drivtrain is loose?

 

I wonder if people with an engine torque brace in their car notice the suddering?

Wait a minute, I just noticed that aaroncake mentioned "has bad spots". Is he suggesting it is defective? If so, how would you check?

 

Not that this contributes any, but my car also does this. Im having TPS problems so this might be the culprit but Id love to fix this.

 

Are you SURE the TPS has to dead spots? How did you test?

 

Try checking the operation of the dashpot, part of the deceleration control system. (FSM F1-71 to F1-72)

To check the TPS measure the resistance of the sensor (FSM F1-83). I assume you have already done this, since you said you had checked it.

 

To test for dead spots do a sweep test...

Check resistance while slowly going through the entire range of the TPS, from fully closed to WOT. It should go pretty steadily from 1k OHM to like 4-5k OHM. Don't quote me on that, the FSM will have the specs.

 

I tested and set the tps using the instructions on fc3pro.com. (http://fc3spro.com/TECH/HOWTO/TPS/tps.html) My car is an S4 NA, but the procedure should be the same.

 

And use an analog tester. It's easier to see the needle drop momentarily.

 

Digital meters are not ideal for this because they have a slow sampling rate. Either use an analog meter or a scope.

 

Thanks. I'll try resetting the TPS with an analog meter and setting the dashpot as soon as I can find a friend to watch the tach.

 

I'm getting this same problem. Did you ever resolve the problem?