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I have a 98 LS400 with roughly 286k miles on it. I've posted before about several issues with the car over time, but this one has me stumped so I'm looking for help before I throw money at it.
Recently I've noticed my car starts to jerk (in a mechanical way- not the human way) whenever I'm driving on the highway and I lightly hit the gas pedal. The jerk only lasts for a few seconds and it feels as if the car is kind "jerking into the next gear". But it only happens when the speed of the car is at 40mph (or generally between 40-60mph.) It seems that above 60mph or below 40mph there is no jerk (or if I push down harder on the pedal verses lightly accelerating).
The second part is, the "jerk" mostly happens whenever the car is on an incline while its driving. (It rarely if ever jerks on flat surfaces). All of that said, one thing I am noticing is that the car feels "heavier" for some reason now. It seems to have lost a little pep and feels more like a heavier car now compared to before these jerks started. (Not sure if its related but just something to throw in there)
I just had the fuel filter changed when I first noticed the problem, but the issue hasn't gone away. My next thought was maybe the fuel pump is going bad! However, my mechanic actually thinks it is a problem in the coil pack rather than the fuel pump. Hmmm!!??
Anyway, I'm trying to get some opinions from Lexus enthusiast here. What do you think might be the likely culprit for why this car starts jerking at 40.
My car does this too. If you stay in that ranged 40-45 and lightly press the gas it'll shudder/jerk and it's somewhat freightening. Would love to know whats going on with it but it's been happening since I got the car 3 years ago.
Does it feel like a driveline vibration? If so, I would highly suggest you inspect your rubber driveshaft couplers underneath the car for any type of cracking.
Even though my car isn't doing any "jerking", I'm replacing my entire driveshaft with those two rubber couplers at 280k due to the rear one cracking fairly badly. I picked up a low mileage driveshaft that had both couplers and the center support bearing for only $55 at the yard off a wrecked almost pristine Coach ed. car. I read somewhere that if you separated the driveshaft, it'll go out of balance, so I removed the entire assembly in one piece and plan to install it the same way in my car to preserve the balance.
I am experiencing almost the same thing. I have a 1991 Toyota Soarer (Lexus) here in Australia. The vibration starts when the car warms up and at any speed when depressing the accelerator. It stops at cruising speed. I have also noticed a ticking sound coming from under the car around the transmission area. It stops when car is placed in drive but keeps going when the car is in reverse. It does not happen every day but the worst is when the car feels like a washing machine. My transmission guys think it might be a torque convertor on its way out so we are getting it inspected.
My LS 400 has been doing the same thing (minus the inclines and heaviness) since I discovered that a very small amount of transmission fluid was leaking even though I'd just had the transmission pan gasket replaced a week prior (2 bolts needed tightening). This weekend I am going to top off the transmission fluid and see if that helps.
Does it feel like a driveline vibration? If so, I would highly suggest you inspect your rubber driveshaft couplers underneath the car for any type of cracking.
The jerking in my car actually feels like something is pulling on the engine from the back in very short successions. I don't notice any odd behaviors in the RPMs or the speed needle movements when this happens. But I suppose in some sense it might feel a little bit like a mistiming.
However, it has this feeling like the engine "pauses" for a second before jumping to the next increase in speed. As a result It feels very mechanical... as in rather than being a smooth increase in speed, its a more like a jump in speed. So the car feels like its "Jumping" from 40 to 42 to 43MPH etc. Again this only occurs when I lightly accelerate in that 40-60 mph range (90% of the time right around 40mph) and generally when I'm on any grade of incline.
That said, its not a vibration (rapid shaking). I haven't had the car looked at mainly due to time constraints but I'm really curious about what I can look for that could help pin point what the issue might be.
Pull the coil packs and make sure oil isn't pooling up in them. Is the check engine light on or blinking when it hesitates? Hows the trans fluid looking -- maybe you're starting to loose 4th gear.
04-13-17, 12:14 PM
Jerking at 40! (no its not what you think!)
