Jerks forward at stop and go (crawling speed) - Your thoughts

[JQ911]

I've had this since I got the car and it's evident only at stop and go traffic at 1st gear only. While I am about to make a full stop (crawling to stop) then traffic decides to move a little, I gently press gas pedal so I can move forward slowly but once pedal is pressed instantaneously the car jerks forward release it and it glides smoothly (sometimes my head jerks as well, lol). It doesn't buckle as if its dying but does the opposite, I believe. Idle is fine not hunting, etc.

Fuel mixture? Vacuum leak?

[Bob Kontak]

Here is my "I don't really know theory" Keep in mind, it is at least worth what you are paying for it.

I think it may be slop in your drive train. Under acceleration, all the parts that are are a little tired, get rammed against another piece of metal regardless of loose tolerances.

You slow down in gear and the mechanical components reverse thrust and the slop goes the other to the other metal side (I think you know what I am saying)

Give it a smidgeon of gas at slow speed and the slop reverses but the engine/trans has a "free" moment to spin up and create inertia then "bang" it grabs.

May be as simple as CV bolts/tired CV's or as nasty as a beat ring and pinion. I don't know how transmissions work inside so can't suggest anything there.

[JAR0023]

Here's my non-professional two cents. Short answer is it may be a little bit the nature of the beast.

Long answer - Always a good idea to be rid of any vacuum leaks. Might want to take a look at your throttle linkage and throttle arm on the side of the throttle body along with the idle switch.

Bentley explains all this in detail. There should be a small amount of play such that when you first touch the accelerator pedal the idle switch closes before the throttle plate opens. Just closing the idle switch should cause the no load RPM to jump as much as 500RPM. There's your lurch. If you don't have that tiny amount of slack and the throttle plate is immediately opening, there's your bigger lurch. Do this at a slow roll with no engine load and you've just played into Bob's Theory of Slack in the Drive Line.

I learned pretty quick to be very easy on the skinny pedal at walking speeds. I also more than likely have the clutch disengaged in that situation to help out as well.

Good luck,
-J

ETA - There is a reversing lever for the throttle linkage on the side of the transmission. There should be a mm or so play here as well. Point being you should have enough designed in play so that you can more than just touch the accelerator before the car takes off.

[pete3799]

Motor and trans. mounts good?

[JQ911]

Bob and J - thanks for the inputs. It seems mine has both of what you said.

Rolling press pedal gently - jerks forward
Rolling no engine load and jerks forward at almost idle speed. What I do is I give a gentle pedal to maintain rolling pace to avoid it from jerking and sometimes I get lucky without the jerk but most often gets it moving forward.

Pete - Motor and Trans mount - No history but in my list for this month, particularly tranny mounts as I feel vibrations on the shifter on heavy acceleration its like the whole tranny is somewhat moving. Could be bushing on mounts are toasted.