auto trans shifting issue

The past few months, after about 15 mins of driving especially on the freeway, the trans on my 97 Tacoma 3.4L 4WD, is slow to downshift at times. It doesn't do it all of the time. It shifts fine in the morning, like on the way to work, but acts up in the afternoon like when I am headed home from work. When I am cruising and step on the accelerator a little, the trans takes a couple to a few seconds to downshift from 4th to 3rd when it should downshift right away and sometimes it won't downshift until I really press on the accelerator. Also, while making a turn at an intersection without stopping, it takes a couple to a few seconds to downshift when I accelerate out of the turn when it should downshift right away. Most of the time, it upshifts fine after accelerating from a complete stop, but every once in awhile, while accelerating when a light turns green, it will shift form 1st to 3rd, skipping 2nd then after a couple of seconds it will shift down to second and then up shift like it should after that. Once I park the truck for a couple of minutes and drive it, again, the trans shifts fine, then it acts up again after a couple to a few minutes.

When it first started to not shift properly, it threw a TPS code, which I replaced with an OEM one, but that didn't fix the shifting problem. It, also, use to throw a shift solenoid code at times, several minutes after it acting up, but it's hasn't thrown the code in awhile.

I had the trans rebuilt a little over 2 years, ago and have been back and forth to the trans shop about it and they are not sure what it is, especially because they can't duplicate the problem when they test drive it, because by the time the shop owner gets into the truck to test drive it, the trans cools down a little. He suggested it could be the TPS, but I told him that I replaced it. He, also, said it could be the shift solenoids, but pulled them out this last weekend and OHM tested them, when I had him bead a trans temp sending unit into the pan and said they were fine. He had the mechanic make an adjustment to the cable a couple of times, but it seemed to help only a little if at all. A couple of months ago, maybe about a month after the shifting problem started, the trans over heated on my way home from work and I had the truck towed to the shop. They pulled the trans out and took it apart and said everything looked fine and were not sure why it over heated, but replaced the torque converter under warranty, in case that was the reason for it over heating.

Anyone have any ideas of what could possibly be going on? I am about ready to say screw it and have him replace the shift solenoids.

 

Could be a worn accumulator piston in/under your valve body. Could also be a piece of debris hanging an accumulator valve in the valve body. Could also be a sticking clutch piston in one of the clutch packs.

I don't know anything about Toyota transmissions (Ford/Lincoln tech, trans for 5 years), but unless you got the right trans guy, intermittent issues are a toss up.

And, as Chris4x4 said, could also be a shift solenoid. But without any Toyota experience, it's hard for me to say

 

As mentioned above , I am also going with a hanging valve body .
When you had the transmission overhauled , did the shop re-calibrate the valve body ?check your invoice .
The trans-go reprogram kit fixes the lazy kickdown and overheating issue .
http://www.transgo.com/products.php...d=253&countdisplay=1&start=0&addcountview=Yes

The Sonnax kit compensates for loss of pressure even in a brand new transmission .
http://www.sonnax.com/parts/2764

To add : just because the shift solenoid has a good resistance check doesnt mean that it will function good mechanically . If the shift solenoids were not replaced when the trans was overhauled , there is a good chance they may have mechanical wear .Only pressure tests can verify this once the trans is hot .


http://www.tacomaworld.com/forum/technical-chat/325531-aisn-warner-340-series-transmissions.html

 

They replaced the valve body with a upgraded one. Which i requested because I tow a pop up trailer with it (which i havent done since the trans was rebuilt.). Up until the downshifting issue, the trans shifted fine since the rebuilt. I do not know if they replaced the solenoids or not when they rebuilt it. The trans guy couldn't remember or not if he changed them and was busy at the time, so i told him don't worry about looking it up, right then.

I was thinking that checking the ohms on the solenoids wouldnt tell you how it was functioning mechanically.

When the trans over heated they went through it and said eveything seemed fine. If i remember correctly they even checked out the valve body and said it was working correctly and the pistons looked fine and weren't sticking. I am hoping it's just the solenoids as chris mentioned.

 

I stopped by the trans shop and talked with the owner, again today and he's insisting that if it's the solenoids, they will either just work or not work. He looked up the rebuild and they did not replace them, because they were fine.

 

Not sure what you have for mileage on the truck but if these are the original solenoids and the truck is a 97 , i would be looking at replacing them as well . I have seen hundreds of solenoids fail mechanically yet still check out fine during a resistance check.
Have you scanned the transmission ECM ? If the trans is skipping 2nd gear , there should be codes stored .
The ball and spring type solenoid allows oil pressure to pass by as it ages and you will not see this with a scanner . Gotta use a pressure tester to verify the mechanical portion of the solenoid . I am still going with a hung valve body .The two links I provided explain in detail the issues that you have according to your description of the problem .

 

Here is a link to some diagnostics and additional info for your trans http://www.tacomaworld.com/forum/technical-chat/325531-aisn-warner-340-series-transmissions.html
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Yeah, I am thinking that I want to have the solenoids replaced, anyway. But, my trans guy doesn't' really want to replace them and find out their not the problem. He wants to drive it when it's acting up to see what it is. But he will replace them if I want to. He said that when he rebuilt it, it had aftermarket solenoids in it. The trans was rebuilt about 2.5 years prior by a shop who took a shortcut by only sanding the clutch plates and not replacing them causing the trans to fail the second time. So, the solenoids may have been replaced, then. Unless they were replaced before I bought the truck. It did throw the faulty shift solendoid code a few months ago several times, but it hasn't thrown the code in awhile.

Thanks for the link, I'll check it out.

 

Just an update. I installed a trans cooler the weekend before last. Today was the first day that it was hot out, since i got it installed (was 97 on my way home) and trans acted up only slightly. Thinking of stopping off at AAMCO to get a second opinion.