Intermittent Buck/Jerk While Driving

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md1twal3

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I've been trouble free with the LS for a few weeks so should have figured another issue would surface. :)

No engine light, no codes and no pattern. I will be cruising down the road nice and smooth and all of a sudden, 1 firm buck/jerk and then the car is fine. It does it randomly and not too often.

I've covered all of the standard misfire issues and fixes and the buck is so strong and isn't like a single cylinder misfire would feel. It's almost like someone is cycling the ignition key very quickly.

Anybody have this happen and can point me in the right direction to figure it out? I was thinking a bad spot/open in the TPS sensor but figured I'd check here before throwing parts at it.
 
It's an LS, so the first question is, when was the last time you replaced all the COPs and spark plugs?

RFI from a marginal COP can actually crash the PCM and cause it to reboot. This rebooting will cause the symptom you describe.

Another thing to look at is the PCM relay in the trunk, and the relay socket. Problems there can cause glitches in the power to the PCM and cause the same symptoms as well.

I'm sure there are other possibilities as well, but those are the first that come to mind.
 
joegr said:
It's an LS, so the first question is, when was the last time you replaced all the COPs and spark plugs?

RFI from a marginal COP can actually crash the PCM and cause it to reboot. This rebooting will cause the symptom you describe.

Another thing to look at is the PCM relay in the trunk, and the relay socket. Problems there can cause glitches in the power to the PCM and cause the same symptoms as well.

I'm sure there are other possibilities as well, but those are the first that come to mind.
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I appreciate the reply. Plugs, COPS, MAF, CAM Sensor, IAC, Fuel Filter, Air Filter and Battery have all been changed within the past several months but I guess it doesn't mean one of the COPS isn't being wierd.

I've got a scanner coming later this week that is supposed to read live data, I'll see if I am able to record a cycle and capture the data at the time of buck.

In the mean time, I'll give that relay a looking over to see if anything is wonky there.
 
Mine just developed the same problem (V6 manual transmission).

I've also thought TPS (had a similar problem years ago with a XR4Ti), but did not want to just replace. Strange that I'm getting no codes. This is why I was looking into a code reader for android tablet.
 
Same engine/trans combo as me, and no codes here either. I do have a spare TPS from an engine swap a while back so may just try it to see.
 
md1twal3 said:
I've been trouble free with the LS for a few weeks so should have figured another issue would surface. :)

No engine light, no codes and no pattern. I will be cruising down the road nice and smooth and all of a sudden, 1 firm buck/jerk and then the car is fine. It does it randomly and not too often.

I've covered all of the standard misfire issues and fixes and the buck is so strong and isn't like a single cylinder misfire would feel. It's almost like someone is cycling the ignition key very quickly.

Anybody have this happen and can point me in the right direction to figure it out? I was thinking a bad spot/open in the TPS sensor but figured I'd check here before throwing parts at it.
Click to expand...

That's how mine started and got progressively worse. EGR.
 
you actually followed all of the steps in the drive cycle, paying particular attn to step 10? if so, i would try doing it again, since its free.
then if its still having a problem i would stress test all the coils, even if theyre new, bc that speed range happens to be when theyre under some of the highest load. if they all pass then youre probably looking @ a TCC or a solenoid.

and i am assuming youre using 91+ octane. if you are, you may want to run a bottle of lucas thru it. its easy and it might cure it.
 
jrand said:
littlerig, keep it up and you will be calling john in tears again.
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Really, I called John in tears ?
Interesting, I recall you belly~aching something about color, was how that started.

run along child, go re~calibrate something ... back on Ignore you go!

finger.jpg
 
you sure did. it had something to do with a picture of joegr, a piece of tape, and the back of your wife's head... how could you forget that? its like your nightly routine, right?

if blocking me is what it takes for you to stop making senseless little comments after every other one of my posts, feel free to do it.

if you dont agree with something someone posts try posting a legitimate response instead of 'bs' or rap videos or random little pictures... i dont even want to know how that barbed wire plays into your obsession with joegr... any more graphic details would probably lead to me blocking you!

and to whoever is going to throw this post out: please recognize the fact that i wasnt even talking to him, he started it with me again. so if youre giving out warnings or whatever, you need to give it to him not me
 
jrand said:
you sure did. it had something to do with a picture of joegr, a piece of tape, and the back of your wife's head... how could you forget that? its like your nightly routine, right?

if blocking me is what it takes for you to stop making senseless little comments after every other one of my posts, feel free to do it.

if you dont agree with something someone posts try posting a legitimate response instead of 'bs' or rap videos or random little pictures... i dont even want to know how that barbed wire plays into your obsession with joegr... any more graphic details would probably lead to me blocking you!

and to whoever is going to throw this post out: please recognize the fact that i wasnt even talking to him, he started it with me again. so if youre giving out warnings or whatever, you need to give it to him not me
Click to expand...

jrand, is this "drive cycle" anything legitimate? from what I read it seems more like snake oil.
 
der3wuste3fuchs said:
jrand, is this "drive cycle" anything legitimate? from what I read it seems more like snake oil.
Click to expand...

Drive cycles are real. You use them to speed up the PCM's learn process after clearing codes or replacing an emissions related sensor. It's good to do if you need to set the monitors quickly so that you can go for an emissions test after a repair.

Beside that, there's no real point to doing it. The PCM continuously learns, so if you haven't recently disconnected the battery or replaced certain emissions parts (like O2 sensors) it won't make any positive long term difference. Even if you have done those things, you don't have to do the specific drive cycle. The PCM will figure it all out after a few trips anyway.
 
not snake oil. its a computer. garbage input = garbage output. if your shift specs are bad/old you car will shift bad/buck/jerk/get worse gas mileage/etc.

yall really didnt give any more info about when your car is bucking/jerking. did the symptom just occur? did you change anything factoring into shift timing (tons of things do on this car) recently before the symptom started?

for starters you need to check the gen 1 service manual bc there may be more/different information than the gen 2 manual. i have a gen2 and they may be slightly different. but if i were you, and i am assuming everything else on the car is in spec with no recent part changes and no overdue maintenance, i would search for the drive cycle procedure i just linked up for user 'stumpie' and perform step 10 of the drive cycle.

if you have other parts that are not in spec then it isnt going to matter. bc coils and all kinds of other things can cause the same symptom. and also if your car has acted like this for more than lets say ~100 miles it may not be corrected by performing step 10 alone. you may need to clear your shift specs and start from scratch bc it has too many clunking/jerking/bucking shifts under its belt and it thinks that is 'normal'. the car is highly adaptive the first few times you start the car after a battery disconnect and it will adapt to however you want it to drive. try following a drive cycle and driving like a madman and see how it shifts. then disconnect and drive really light and see how it shifts. there is a very wide band in which the computer will schedule your shifts. it will compensate for failing parts over time, so when you replace parts the computer still has the specs from the old part. thats a great time to clear the computer and start fresh
 
joegr said:
Drive cycles are real. You use them to speed up the PCM's learn process after clearing codes or replacing an emissions related sensor. It's good to do if you need to set the monitors quickly so that you can go for an emissions test after a repair.

Beside that, there's no real point to doing it. The PCM continuously learns, so if you haven't recently disconnected the battery or replaced certain emissions parts (like O2 sensors) it won't make any positive long term difference. Even if you have done those things, you don't have to do the specific drive cycle. The PCM will figure it all out after a few trips anyway.
Click to expand...

in theory, yes it will eventually learn something. my point is simply that by doing specific targeted steps to set the sensors how you want you can control what the car learns and can change its behavior & strategies.

the buck/jerk btwn 40-55 is due to the pcm (computer) engaging/disengaging the TCC (torque converter clutch). in toher words: it cant quite figure out if you want to shift/downshift based on how hard you are pressing the accelerator. to calibrate the sensor that controls this in a genII (i cant speak for genI) you need to follow step 10 on the drive cycle chart. i can guarantee you that no one in their right mind completes step ten more than once a year, if they even do it in ten years... therefore most people never properly calibrate the sensor in question and get the symptom in question, though the symptom can be exacerbated by a litany of other problems (ie coils, improper octane, dirty maf, dirty throttle, the list goes on)
 
Guys....you're going down the wrong path...the problem is occuring on cars with 5 speed manual transmissions...
 
md1twal3 said:
Guys....you're going down the wrong path...the problem is occuring on cars with 5 speed manual transmissions...
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I don't believe I've gone down the wrong path.
I'm sticking with the Marginal COPs or PCM relay.
The EGR suggestion is not unreasonable at all either.
There are, of course, other possibilities.

I can only imagine what jrand is saying (ignore list).
 
i was talking to the ppl above who have an auto.
i dont have a manual, couldnt tell ya. but i would guess at least one coil wouldnt pass a stress test.
bahaha i could have swore someone up there had an auto..
 
jrand said:
bucking symptom occurs btwn 40 and 55 mph, no?
Click to expand...

No,

I've had it at 70 and at 25. Never when accelerating only when cruising at semi steady speed. This is why I thought TPS . Not very frequent. With the XR4Ti I disconnected the TPS (as a test) and the car ran better not bucking at all (it would idle at 1500). Changed the TPS and the problem was solved.

I just got my rear calpiers from Rock Auto so maybe after I'm done changing them I can get some time to figure out this problem.

BTW car has 156,000 miles if that matters.
 
Mines doing it too - but only when it's snowing. Even a light snow. It almost stalled on me this morning (cold start, not up to running temp, snowing) coming to a stop.

I've had the buck at just about any speed. And it either happens when cruising or in between hard (near WOT, let off to shift, back to near WOT) shifts.

I know I have a bad TC, and I'm beginning to wonder if that is the cause of this... Just haven't found enough time to pull the trans (my other car still needs a steering rack and windshield before its driveable).
 
Thanks Joegr and Jrand, I was leaning toward thinking the computer would adapt over time and just re-learn anyway.

It seems that I actually have the problem with the TCC as you mentioned. I'm fairly certain it's the dirty MAF or coils as I recently purchased the car and I can tell the last owner was very lazy.

I'll give it a shot and read through the Alldata.

Ian.
 
pragmatic said:
No,

I've had it at 70 and at 25. Never when accelerating only when cruising at semi steady speed. This is why I thought TPS . Not very frequent. With the XR4Ti I disconnected the TPS (as a test) and the car ran better not bucking at all (it would idle at 1500). Changed the TPS and the problem was solved.

I just got my rear calpiers from Rock Auto so maybe after I'm done changing them I can get some time to figure out this problem.

BTW car has 156,000 miles if that matters.
Click to expand...

i have an 05v6 (auto), when my coils were marginal it would buck at a wide variety of speeds, but definitely when shifting between 4-5, 5-4. it would often go into limp mode and throw throttle-related codes, though the throttle was not the problem. the coils were the problem. that is supposedly unrelated RF interference. i would imagine a failing TPS would/could cause the same symptoms though
 
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