92GS603
Proven Member
- 31
- 0
- Mar 9, 2014
-
Southern,
New_Hampshire
Let me just say that I've had this issue for a long time now, but it's become such an annoyance that almost 2 years after it started, I'm finally sick of it and seeking answers. Title says it all--If I quickly go onto or off of the throttle, or hold the throttle between 0-15% (guessing, but basically just enough to hold a steady speed), the car bucks. It does it in every gear, and is most pronounced when slamming the gas pedal to accelerate hard. It starts out during early warmup with a delay (let off throttle, then bucks after a 1-2 second delay). There is also an occasional instance of rough idle, but its fairly rare.
Since it started, the following parts have been replaced due to failure or out-of-range operation.
-MAF (IAT sensor was way off) --didn't help bucking at all
-IACV (flat-out died) --didn't help bucking at all
-Coolant temp sensor (was reading way off) --moderately reduced the severity of bucking
-Plugs and wires 2 times (20k miles, first set of wires rubbed on other parts til they started arcing) --little to no change
-O2 sensor (old one was dead) --little to no change
I have also replaced the PCV with a new OEM one, and have replaced the fuel filter and ran BG44k through twice. I have not had a chance to check the fuel pressure, but the fact that the bucking is delayed during the early warmup period makes me believe it's a sensor and also rules out it being drivetrain/transmission lash.
As for the other things I've tested, here is what I got:
TPS: 600-5000 ohms from 0%-100%, no weird spikes or dips but the low bottom end makes me suspicious, as it's supposed to be ~1100-5500.
With the harness attached it's putting out .48v at closed which is within the range that the Haynes says it should be, though I'm very tempted to adjust it up above .50v just to be safe.
Coil Pack: Primary resistance is around .9-1.0 ohms when cold and just slightly higher when hot. Secondary for both coil sets is around 13k cold and 15.5k hot. Seems slightly out of range.
Closed throttle switch: Operating properly
Vacuum system: No leaks that I can find, idle is VERY smooth for a DSM.
I have yet to check the CAS or power transistor, but my understanding is that either of these going bad usually causes you to lose 2 cylinders. Keep in mind that this is also a non-turbo daily driver, so I don't have any A/F gauges or access to tuning software to let me see all of my sensor values on the fly.
Since it started, the following parts have been replaced due to failure or out-of-range operation.
-MAF (IAT sensor was way off) --didn't help bucking at all
-IACV (flat-out died) --didn't help bucking at all
-Coolant temp sensor (was reading way off) --moderately reduced the severity of bucking
-Plugs and wires 2 times (20k miles, first set of wires rubbed on other parts til they started arcing) --little to no change
-O2 sensor (old one was dead) --little to no change
I have also replaced the PCV with a new OEM one, and have replaced the fuel filter and ran BG44k through twice. I have not had a chance to check the fuel pressure, but the fact that the bucking is delayed during the early warmup period makes me believe it's a sensor and also rules out it being drivetrain/transmission lash.
As for the other things I've tested, here is what I got:
TPS: 600-5000 ohms from 0%-100%, no weird spikes or dips but the low bottom end makes me suspicious, as it's supposed to be ~1100-5500.
With the harness attached it's putting out .48v at closed which is within the range that the Haynes says it should be, though I'm very tempted to adjust it up above .50v just to be safe.
Coil Pack: Primary resistance is around .9-1.0 ohms when cold and just slightly higher when hot. Secondary for both coil sets is around 13k cold and 15.5k hot. Seems slightly out of range.
Closed throttle switch: Operating properly
Vacuum system: No leaks that I can find, idle is VERY smooth for a DSM.
I have yet to check the CAS or power transistor, but my understanding is that either of these going bad usually causes you to lose 2 cylinders. Keep in mind that this is also a non-turbo daily driver, so I don't have any A/F gauges or access to tuning software to let me see all of my sensor values on the fly.
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