Ares

Had this problem since I bought the truck a little bit ago.

When driving, if you let off the throttle, the engine jurks, kinda lurches forward. When you apply the throttle, it jurks again. These are hard jurks. Like spill your coffee. As long as you keep the thottle open, its fine. Or you can ride it with the clutch to smooth it out.

I tried tightening the throttle cable to hold the throttle open a little, but that didn't make a difference, still jurked. So, maybe a fuel issue? Anyone else ever have this problem.

This is on a 22RE 5spd. Thanks

jason191918

I have this problem w/ a manual at high rpm's. Believe that is normal.

Matt16

Mine does it too (4cyl, 5spd). I think its normal. Could be a worn out dashpot though. I just ate Thanksgiving turkey dinner, so I'm not about to explain dashpot, google it.

abecedarian

any sort of jerk during transition to on or off throttle is not normal under any circumstance.
a hard jerk may be engine mount related.

space-junk

iTrader: (1)

mine does it too... only way i figured to get around it is to REALLY slip the clutch... but i dont suggest it...

Matt16

I wouldn't call it a jerk, its just what the OP used. When you are at high rpm, low gear (especially when the engine is cold) and let off the gas going down hill, the engine initially provided little braking, then decides to cut fuel and then its like you tapped the brakes.

I think its a worn dashpot, but thats about the last thing in the world I'd worry about, unless it bothers you a lot.

abecedarian

but it's described as "When driving, if you let off the throttle, the engine jurks, kinda lurches forward. When you apply the throttle, it jurks again.".
nothing about low gear, high rpm is mentioned.

I might be inclined to think a problem with the AFM, but I'd have to have it tested to be sure. Otherwise, I'd file it under intake vacuum leak or timing issue for now.

Ares

Right, its not related to RPMs what-so-ever. Completely independent.

I just completed a motor swap (old motor had a rod through the block), but it did this before the swap too. So I know for a fact there are no vacuum leaks. The motor mounts appeared in fine shape. I was told when I bought the truck the AFM was new, but I'll test it just to be sure....since the engine that blew was supposed to be rebuilt...

And we're not talking about a little jurk like tapping the brakes, or hitting a bump. We're talking a strong jurk, similar to hitting the parking curb at 5 miles an hour, or a low speed accident. Its beyond bothersome.

I don't think it can be dashpot. Those are AT only, according to the FSM.

Ares

Just thought of something important. This does not happen when not driving. So if you rev it up in the driveway, letting off the throttle will not jurk the engine. Only when moving does this happen....

So...now is probably something related to the power transfer to the wheels....hmmmm.

space-junk

iTrader: (1)

might be related to some play in the driveshaft and rearend... thats what i think mine is... i mean, mine jerks, but its not like hitting a burb... it annoys my girlfriend which is a plus...

Matt16

I have an auto locker so there is a lot of play (backlash) inherent to the design.

wardriver

So...it does not do it when you are driving...and you swapped the engine. What is still there from your old engine?

Ares

No, it only does it when I am driving. It does not do it if its just sitting in the driveway. And yes, it was present before the engine swap...

PapaChulos4U

Dashpots are not just for autos, I have a 5 speed and it has a dashpot. All it does really is act as a cushion to slow the closing of the throttle so it doesn't just come to a sudden halt and jerk like you're talking about. Mine did that for a while (actually, until just yesterday) after I reset the AFM and was annoying as hell, almost like I was slamming on the brakes for a second of two.

Also, check the Throttle Position Sensor. If it's angled down too far, it will not know when the throttle has been pressed or released so it will stop too quickly (jerk) or be sluggish on takeoff. You can set it to about halfway (using the slots as a guide usually is enough, you can be precise if you want, not a biggie) or do as I did and angle it about 45 degrees upward to advance the sensor, gives you a bit more power and the throttle feels tighter, just adjust your idle. Also, adjusting it is a pain, I had to take the throttle body completely off to avoid the vacuum/radiator hoses.

Hope this helps.

dropped_dime98

Mine does this while driving. Not really rpm related also itll kinda jerk a lil and even when i go to give it gas itll jerk some more (not bad just a jerk every 2 seconds or so with just a lil throttle) then after giving it gas for a little itll catch back up and haul butt. But im gunna have my mechanic check it out today and see what he comes up with.

Ares

Sorry I disappeared, I've been gone for a little while. But you actually read my mind.

I swapped the new TPS onto the throttle body I was going to use. I adjusted the TPS till the ohms deflected like it said, but they may not be deflected enough. The ohms start at 0, then hit 25 for a split second before jumping up to over 300. I set it to the 25 ohm deflection, maybe it should have been to the 300. I'll flick it a little tomorrow and see what happens...

And yes...complete PITA. You cannot access that bottom screw worth crap with the intake body installed.

After I do that I'll reboot it all and see if it helped.

Thanks again

abecedarian

actually, the dashpot does more than that. by slowing the throttle plate down when closing, it prevents the AFM from closing completely (due to inertia) which prevents backfires as well as the lean mixture condition that would occur, thus raising NOx emissions. It's not a simple device that prevents 'jerking'and any time the throttle position sensor / idle speed are adjusted, you should do the timing as well

The TPS is not a device that can just be angled to whatever setting you think works. There is a fairly specific adjustment that must be made to it, very dependent on measurments to the thousandths of an inch. It tells the ECU when the throttle is fully closed and how far the throttle is open.
When you're adjusting it, there are two sets of readings that must be made.

Ares

Hence that whole para about the ohm readings. The difference between the 25 and 300 ohm resistance in the TPS was about less then 1 degree of rotation. And of the three readings you can take to check the tps, only one is improtant for setting the tps, which is fully closed (or shimmed if your stop screw isn't attached to the 4wd vsv), which is what that reading is for.

Now that I'm looking at the FSM instead of the Chilton (which just said to look for a deflection when installing), its specifying 0.2-0.8 kohms resistance, so the 25 ohms resistance its set at is wrong It'll give me something to do tomorrow.

I'll let you guys know if this helps anything

kauai808

every one say its normal but its not. mine did that to. all you do is put sea foam in the air line, suck about half the can it and let sit for about 5 min. thats what did it for me

Jay351

Mine does it, I have a feeling is the driveline slack. Rear locker, r150 tranny + worn dashpot =