Car lurching at steady speed

[batmobilefrs]

So when I'm driving at a constant speed the car will begin to lurch as if it wants to stall but doesn't. I just had the fuel pump replaced by the dealer to fix the chirping issues and the only mod I have in the engine is an AEM intake. They told me it was bad ECU software and they rehashed it with brand new updated software and that still didn't fix the problem. Wondering if anyone else has seen our heard of this. Car is back at the dealer right now and I'm just wondering what kind of b.s. they might try to throw at me and if any of you all have suggestions.

[Bg8780]

I've heard some hear-say about some dealers not doing a very good job on fuel pump installs. Maybe a botched install and it's starving the car. Just a thought, I have no idea what I am talking about.

[strat61caster]

Is this before the engine warms up, you're in first gear and under 10 miles an hour?

[Zach3794]

I had the same issue at normal driving speeds and this was my own in tank fuel pump install error. Seeming as yours appears to be stock, not sure what it is. Slight lurching under 10mph in first gear is normal.

[qqzj]

Originally Posted by Zach3794

Slight lurching under 10mph in first gear is normal.

Why is that? Thanks in advance for the explanation.

[Zach3794]

My best educated guess is not enough engine load combined with not being up to operating temperature. Happens to me every day of the week, rain or shine since I've owned the car.


Sent from my iPhone using Tapatalk

[strat61caster]

Originally Posted by qqzj

Why is that? Thanks in advance for the explanation.

There's a mismatch between the load on the car and the power the engine outputs, the engine goes 'oh shit' and compensates by adding gas to prevent a stall lurching forward and starting a vicious cycle of speeding up and slowing down because it's trying to maintain a set idle speed. An AT will smooth this out with the torque converter but a MT has a direct mechanical connection between the wheels and engine so you either got to give it some gas or pop in the clutch.

Of the few MT cars I've driven this has always been true, reducing the lurch would involve raising the idle speed to the car can apply more consistent power, sacrificing fuel economy and comfort levels (lower idle speed is quieter). When the car warms up it can provide a stronger more consistent idle so the problem is reduced.

I may be missing something but that's my explanation.

[Poodles]

Lurching at low speeds is also going to be drivetrain lash (mounts, sprung clutch disk, etc)


It's typical for a MT car unless you modulate the clutch a lot.

[jhh3000]

OP - can you give some more detail? i agree with everyone on this post; if you're in 1st, under 10mph, and not being careful with throttle, you'll end up with wave-like lurching where the car speeds up and slows down rhythmically. usually can be easily corrected by hitting the clutch or giving it more gas.

that being said, i have noticed that the clunking from gas-on to gas-off in 5th and 6th gears is getting worse. used to be not noticeable at all, but now i can feel it in the chassis.

[batmobilefrs]

Originally Posted by jhh3000

OP - can you give some more detail? i agree with everyone on this post; if you're in 1st, under 10mph, and not being careful with throttle, you'll end up with wave-like lurching where the car speeds up and slows down rhythmically. usually can be easily corrected by hitting the clutch or giving it more gas.

that being said, i have noticed that the clunking from gas-on to gas-off in 5th and 6th gears is getting worse. used to be not noticeable at all, but now i can feel it in the chassis.

So after much headache i found out that my AEM intake has a piggyback on the MAF to control the fuel/air mixture to give better HP gains. Well, said chip malfunctioned and was simply telling the computer to FUEL!!!! So essentially it was flooding my engine out for a week straight. As this is not stock and I took it to Toyota to fix, it was not covered under warranty. I contacted AEM and told them the problem and they readily agreed to refund the money for the intake and the cost of the repair bill. Problem is solved but unknown ammount if any long term damage is done to the engine.

[DarkSunrise]

Originally Posted by jhh3000

that being said, i have noticed that the clunking from gas-on to gas-off in 5th and 6th gears is getting worse. used to be not noticeable at all, but now i can feel it in the chassis.

I notice the drivetrain lash in 5th and 6th.

Does anyone get a lot of lash in 2nd as well? For example, clutch engaged, when you're off the gas then hammer it in 2nd? On my car, you can feel a split second of play/slop before it feels like you're getting rear-ended when everything catches up to the engine.

I had someone rev the engine while I popped the hood, and there's minimal movement, so I don't think it's the engine mounts. My guess is there's a lot of movement in the rear differential. Perhaps it's time for rear differential bushings.