So I have looked on the site and Google for the last hour or so and I've found a dozen different fixes for this problem including replacing the 3rd and 4th valve's, plugs, air filter, friction coefficient modifier in my ATF, ATF flush, etc.

I assume what will happen is I will describe the problem and then get 20 different answers but in the off chance that I just haven't stumbled upon the thread with the answer here goes nothing.

Bought an 02 TL-S with 125k and it ran fine for a few days and I've been pricing out a timing belt kit and getting ATF and plugs and an air filter and just usual preventative maintenance stuff and before I could do any of that the car shuddered getting on the freeway 2 minutes after starting it one day at around 3k RPM's. It only did it once and there was nothing after the rest of the day. I thought maybe it was plugs or whatever.

It did this a few more times the next day but mostly at like 2k RPM in low gears and no amount of throttle will fix it like is often the case with a misfire from plugs (I also assume a misfire would pull an engine code and there are no codes). It has never done it on the freeway at 70 mph and roughly 2k RPM's and I can even modulate the throttle at higher speeds with no problem. When it does happen letting off the throttle appears to let the car idle just fine and it hasn't died yet. I replaced the plugs anyway and the valve cover gaskets because they were leaking and the shudder is still there (I'm not really surprised).

My question is, is there a good way to do a differential diagnosis on IAT sensor, trans ATF, Trans 3rd and 4th valve, etc?

Thanks for any help

 

I forgot to mention. The transmission was already replaced in 06 at 60k miles

 

Change the 3rd and 4th gear pressure switches. Get a case of dw1. Also you should replace the spin on filter ontop of the trans underneath the battery box. Do a 3x3 drain and fill with driving in between. Clean your solenoids and check them for clicking and resistance. If out of spec or no clicking replace bad solenoid. Clean the grounds on the trans. Check your trans mounts and the front engine mount. Replace if worn out. Also check the vacuum lines going to the mount. Check your axle seals to make sure they dont leak. Other than that I can't think of anything else. There is no guarantee any of those things I listed will fix your shudder or prolong the life of the trans but its about the only thing you can do.

 

^ all good things to check. You may have come across a thread of mine while searching, but I have also had the same issue. Once in a while within the first few miles of driving I would get a quick shudder and then usually nothing more after that. I also had some slight shudders or like a pulsing feeling at low speeds low rpms. Some lubegard red seemed to take care of that. But however, within the last 1000 miles or so my trans has all of a sudden started acting up at low rpms at any speed between say 20-55. Sometimes more random than others. I have changed the fluid 3x over just recently and it remains clean. If I drive in d4 it does not do it whatsoever. Seems others have had this same experience. From what I gather, it is the clutch in the torque converter not able to hold at low rpms. It starts to slip and shudder. Apparently driving in d4 won't allow the clutch to engage hence no shudder. At least this is what I believe is this case... If I get on the highway above 55-60 I then go into D5 with no problems. Questions how long can it go driving in D4.

 

Thanks. That is very helpful. I am going to do the 3x3 flush and inline filter change and then try driving in d4 and see if that effects anything. I will let you guys know.

Also, I thought the 3rd and 4th gear relays were for smooth shifting in those gears and not related to the overall failure of the transmission (which seems to be 3rd gear more often than not). Is it the harsh shifting into 3rd combined with the fragile nature of 3rd that creates changing the relays being good? I know this is a side note I was just curious.

 

not relays- pressure switches with screens inside that get clogged up and can be cleaned

try this for clutch wear test: after driving normally for 30 minutes so trans is nice and warm, get on freeway at full throttle from 20 mph- as if a semi was breathing down on you!
if the 2nd-3rd gear clutch packs are worn you will get some slippage like a manual trans car with bad clutch- rpm goes up but not speed
Also watch for a momentary flashing D5 light on dash- where none has been seen before
that's a bad sign

when slowing normally- does it gently downshift and idle fine?

when doing the atf drain and refill- there is a specific procedure for drive between drains- chances are you still have the old formula zr1 atf- new stuff is called DW-1
From the first draining take a 3 ounce sample of the atf and send to blackstone labs with 20 dollars
a mass spectrograph reading will tell if there are bad things in the fluid- like clutch material

we suffer from certain wear that sends clutch particulate matter into the torque convertor where it gets stuck and tries to escape thru the outlet screens into trans, when screens clog it wont shift anymore! wait 30 minutes and it will be good again- after crud falls off the screens

quit reading online and use azine as your source of good info
we actually drive a TL and have suffered its few problems, so an answer here is real info

 

D4 is fine to use forever- will slightly drop freeway mpg but other than that its just an over-drive gear with reduced rpm on freeway

 

Sorry, yes they are pressure switches/valves. I don't know why I said relays. I changed out the fluid and it went very well and the shifting is smoother now but it wasn't rough to begin with. There was also very little residue on the magnetic plug. The bog is still there and I am suspicious that it doesn't have anything to do with the transmission.

I've narrowed it down a little. First, the more I open the throttle when it happens the more it lowers the RPM and if I let off the throttle all together you'd never know anything was wrong. Second, it only happens when the car has already been driven once in the last 3-4 hours (it won't happen in the morning or after I've been at a friends house for 6 hours). Even then it will only happen for the first minute or so after I start the car and it only happens at low speeds (under 15- 20 miles per hour). Also the put it in D4 doesn't do anything. I tested the clutches from about 5 miles per hour in 1st through 4th shifting at 5-6k RPM's with very crisp engagement of the clutches.

I will experiment tomorrow with revving it in neutral and letting it sit and warm up before driving to see if that eliminates the problem. Let me know what you guys think.

 

that's not how you test out clutch problem, requires warm trans oil and jumping on throttle at 25mph -repeat several times to really heat things up
If its going to slip due to worn clutch it will then (usually 2nd or 3rd gear clutch packs are the problem)

have you looked at PCV, egr cleanout inside intake manifold, cleaned TB and IACV
with at least some carb spray thru TB?