Car lurching...studder while driving
 

Hello G Community!

I'm experiencing something strange with my 2003 6MT coupe. The past 2 mornings on the way to work I've experienced a brief lurch/studder while driving. It's like 3 to 4 quick consecutive jerky lunges, then it stops. It feels as if the engine is sputtering or the car is slipping out of gear. Both times it's happened in almost the exact same spot/distance from home, cruising in 4th gear going approx. 40-45 mph on a flat, straight stretch of road. I wouldn't say the car is cold because it has happened about 5 mins from home and the car had reached operating temp. Today I felt an additional slight lurch while in cruise control on the highway in 6th gear going approx. 70 mph.

Any ideas what would cause this? Is this something engine related, or transmission? Am I experiencing a misfire? Belts slipping?

I used to get a jerk just like that on my '04 6MT when cruising down slight inclines at lower speeds back when my car had OEM rubber for the driveline. Basically the cruise control is getting confused by the amount of slack in your driveline and "bouncing" back and forth between both extremes in situations where cruise control is on and off the throttle due to the downward incline.

After replacing:

Engine mounts
Differential mounts
Transmission mount

The slack was reduced to where cruise control was smooth again, but can still induce the same jerk in lower gears manually on/off throttle (there's backlash elsewhere, it's 16 years old)

Problem could also be caused by

Center support bushing
Excessive backlash in diff
Loose U-joint
Loose axle shafts
Failed dual mass flywheel

but all those would cause other vibrations which you'd care more about than this jerk.

Nothing to worry about if you're not beating on your car, just age related problems from rubber wearing out. I'd start with differential mounts, then engine mounts, and go from there. Depending on what it is it will progressively get worse until something breaks, but definitely not something you need to stop driving your car for just take it easy.

Thanks for the reply, however, the 2 morning occurrences yesterday and today we're during normal driving without cruise control engaged. Just maintaining a constant speed with foot on the throttle.

I'd pull the spark plugs and check them. Probably early signs of a cam or crank sensor failure though.

Thank you for the suggestions. Would a faulty cam/crankshaft sensor throw a CEL code?

Damn I was excited to share that since I was asking about that awhile ago with no replies. Definitely sounds like engine issue then.

It normally would throw the idiot light but might not yet since its intermittent... check for pending codes?

Lol. You'll save the day for someone eventually.

Sounds like it's about that time for me to finally invest in an OBD-II scanner. Hopefully it's the plugs or sensors as those are on the cheap end as fixes go.

Yep sounds like cam/crank sensors.

How many miles you got? $150 replaces cam and crank sensors with Hitachis which you know you're going to need anyway if you drive your '03 enough.

Mileage isn't really a good metric since it fails when oil begins to seep past the seam in the plastic casing. That's mostly due to the age of the plastic.

How does the crankshaft sensor fail then? Water exposure?

Pretty much, anything that gets into that internal winding screws up the resistance and thus voltage being sent out.