Shuddering when letting on or off the accelerator
10-06-06, 11:02 PM
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Shuddering when letting on or off the accelerator
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?
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?
10-06-06, 11:57 PM
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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.
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.
10-07-06, 12:39 PM
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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
10-07-06, 02:03 PM
#6
The Cause of Death
Originally Posted by svs
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
10-07-06, 02:08 PM
#7
The Cause of Death
Originally Posted by spot_skater
When you set it, you set it when the car was warmed up, right? Just want to make sure.
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10-07-06, 02:41 PM
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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.
I’m going to get in on a lift for another look at the diff this afternoon.
10-07-06, 03:12 PM
#10
The Cause of Death
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...
10-07-06, 06:52 PM
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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?
Wait a minute, I just noticed that aaroncake mentioned "has bad spots". Is he suggesting it is defective? If so, how would you check?
Last edited by sniperstevedave; 10-07-06 at 06:54 PM.
10-08-06, 11:25 AM
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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 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.
10-08-06, 11:29 AM
#18
The Cause of Death
Originally Posted by sniperstevedave
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 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.
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.
10-08-06, 04:21 PM
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Originally Posted by Aaron Cake
Are you SURE the TPS has to dead spots? How did you test?
10-09-06, 07:53 AM
#20
Originally Posted by spot_skater
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.
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.
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