[clyder]

Difficult to describe.
Driving along and there is a VERY fast hesitation, almost like the wheels are partially locked for a thousandth of a second. Very noticeable, feels like you are being bumped forward and then it is gone.
Usually it is just one time, once it happened 3 or 4 times in quick succession.
Happens regularly, I have had the car about 6 months and it did it the whole time.
Other than that the car runs great, very slight shake at idle, transmission (?) whines so you can hear it, downshifting bumps to first sometimes.
Any ideas would be appreciated.
Thanks in advance!
Clyde

 

[douggro]

Check the trans fluid level when it's warm (after driving 20 minutes) and make sure you're topped up. Use ONLY ATF+4.
The downshift bump may be the solenoid pack starting to fail, if the fluid level is correct and the fluid is good.

 

[clyder]

I checked the trans fluid when I got the vehicle and the last time about a week and a half ago.
Shows in acceptable range each time.
How long does it take for the solenoid pack to completely fail?
Thanks.

 

[cvguy]

... very slight shake at idle ...

If it were mine, I'd try to get that figured out and fixed before spending a lot of time on the transmission. Have you pulled the spark plugs recently to check their condition and to see how they're firing? The whine could be simply caused by a clogged power steering reservoir, which is very common on our vans.

 

[marvinstockman]

Fuel or ignition cutoff can feel like a bump stop, as I've been there and done that.

If the tach drops like a rock, I know it's hard to monitor, though the Torque App, bluetooth adapter, and an Android phone, can record the tach, it can be an ignition problem. Fuel would be fuel pressure, but that is harder to monitor.

 

[douggro]

How long does it take for the solenoid pack to completely fail?

No discernable timeline for solenoid packs to fail. When they go bad, you'll know it right away: CEL will light up and you'll be in LIMP MODE. Signs of possible impending failure are slow engagement into gear from P or N accompanied with a "buzzing" noise from the solenoid pack.

The hard downshift bump may also be a sign that the solenoid was previously replaced and the TCM hasn't learned the shift points properly. A transmission shop can run a Quick Learn on it to reset it.

 

[clyder]

Thanks for the replies.
The van has 56,800 miles on it. Haven't checked the plugs. Averages 19 mpg just around town. The slight rough idle might relate to the A/C starting and stopping. It is very slight.

The trans shifting from P to drive does seem slower than normal but there is no discernable noise (buzzing) accompanying the shift. Is there something else I could check for?

As to fuel or ignition cutoff: this "bump" does not feel like taking your foot off the accelerator, which is a soft slow down. So I imagine the computer disengages the transmission from the engine when that happens. With a cutoff of fuel or ignition would the trans still be engaged and a pronounced bump (slow down) be produced? How would you test for this possibility without the equipment you reference? I'm a backyard mechanic with some tools, nothing fancy.

 

[douggro]

With the solenoids, sometimes there is no buzzing when they are going bad. They just get slow to engage. In fact, a little buzzing from them is normal and some vehicles had sound insulators around them to mitigate the noise. But slow / harsh engagement into gear can be a sign of a failing solenoid, or low fluid level.

I'd pull the plugs and check their condition as cvguy suggested WRT the shake at idle.

 

[clyder]

Thanks for all the responses and ideas!

 

[Carbuff2]

Most transmission solenoid packs are replaced because they leak fluid, not because they malfunction.

Yes, the solenoids buzz when shifting into gears (reverse to drive, as an example). You can hear it distinctly when the windows are down.

 

[clyder]

Thanks for the info!