Runner acting up when its warm out

[CrazyMofo]

Hey Guys, newb to the board here(1st post). I tried the search button, but came up w/nothing. Hopefully you guys can hook a brother up.

Tell me whats wrong w/my car. 1998 Toy 4Runner LTD V6 /150K/ Automatic Trans/Newly changed trans fluid, and Newly flushed coolant/Last tune up approx 2yrs ago (I think?)

Problem A: I've noticed this for some time now: Im driving on a highway (steady speed 80mph) then suddenly my RPM's start pulsing (feels like Im stepping on/stepping off the accelerator) it sometimes lasts 10-30min. It goes away when I accelerate (then it happens again, a few mins later?)

Problem B: Now this only seems to happen when it's warm outside: Normally most A/T are 4speed correct? Well, just last week when the weather was much colder, When Im driving (from a complete stop, the car will shift through the gears (like its suppose to) Now as the weather warms up (60+deg F) my car doesn't want to shift into (4th O/D) (example) Normally at 80mph my RPM's=2,400. When (the car is acting up) my 80mph RPM's=3,300+

Problem C: When driving at highway speed (ie 80mph) and I let off the accelerator(completely), it feels like the car is downshifting from 4th to 2nd. Normally if you'd let off the accelerator you'd barely feel a thing. This happens about 99% of the time. Whats up with that?

I dont know if its the transmission, cause the car will accelerate w/o hesitation and w/o slipping. One mechanic told me it might be my coolant/solenoid (either the coolant is old or there's not enough in the radiator) I went as far as getting the coolant flushed the other day (just to make sure). Thought my problem was solved cause the car ran flawless this am, then when it warmed up it went through prob A+B.

I don't know what else is wrong. Any ideas/suggestions?

 

[CrazyMofo]

Im stumped, tried all kinds of google searches.

 

[tomhaney1]

I had the same problem with a Mazda 626. I could never figure out what was causing it or how to fix it. Sometimes it would happen, sometimes it wouldn't. The car did have major transmission issues though. Maybe the torque converter is not locking up fully or erradically?? I have really no clue though...we went through the entire spark/ignition system, all sensors, all valves/seals, emission system etc. and never found the problem. Good luck man!!

 

[JP4RNR]

For 1998 4Runners

Sounds like the Lock-Up clutch in the torqe converter is slipping. When the transmission heats up the fluid gets thinner. Maybe there is a degradation in fluid pressure when the trans heats up. There is also a lock-up relay valve in the valve body that triggers the lock-up mechanism. I would look to the valve body as the culprit of all of your issues with the transmission. Now that I think of it lack of fluid pressure in the trans would cause all of these issues. The governor is responsible for increasing fluid pressure in relation to vehicle speed, the faster the speed the higher the governor pressure. Throttle pressure increases as the throttle is opened. It's the battle between throttle pressure and governor pressure that control the shifting of the transmission. If governor pressure is greater than throttle pressure then the trans will upshift. If throttle pressure is greater than governor pressure the trans will downshift.

If the governor pressure is low the trans will "think" you are going slower than you actually are and will choose a gear based on the speed the trans "thinks" you are going. Lock-up only occurs at speeds greater than 45MPH in O/D only. If the the governor pressure starts to fall or fluctuate you will feel the pulse like the lock-up clutch is engaging and disengaging, which it is because it intermittently has enough fluid pressure to keep the clutch engaged until the trans gets hot enough for the fluid pressure to fall in turn disengaging the clutch.

If your transmission is going into second gear with zero throttle pressure that makes the governor pressure suspect. I would have the valve body checked/ rebuilt. weak spring pressure on the valves in the valve body could cause poor fluid pressure

 

[CrazyMofo]

For 1998 4Runners

Sounds like the Lock-Up clutch in the torqe converter is slipping. When the transmission heats up the fluid gets thinner. Maybe there is a degradation in fluid pressure when the trans heats up. There is also a lock-up relay valve in the valve body that triggers the lock-up mechanism. I would look to the valve body as the culprit of all of your issues with the transmission. Now that I think of it lack of fluid pressure in the trans would cause all of these issues. The governor is responsible for increasing fluid pressure in relation to vehicle speed, the faster the speed the higher the governor pressure. Throttle pressure increases as the throttle is opened. It's the battle between throttle pressure and governor pressure that control the shifting of the transmission. If governor pressure is greater than throttle pressure then the trans will upshift. If throttle pressure is greater than governor pressure the trans will downshift.

If the governor pressure is low the trans will "think" you are going slower than you actually are and will choose a gear based on the speed the trans "thinks" you are going. Lock-up only occurs at speeds greater than 45MPH in O/D only. If the the governor pressure starts to fall or fluctuate you will feel the pulse like the lock-up clutch is engaging and disengaging, which it is because it intermittently has enough fluid pressure to keep the clutch engaged until the trans gets hot enough for the fluid pressure to fall in turn disengaging the clutch.

If your transmission is going into second gear with zero throttle pressure that makes the governor pressure suspect. I would have the valve body checked/ rebuilt. weak spring pressure on the valves in the valve body could cause poor fluid pressure

Wow, I didn't think the issue strecthed that far. I thought it was simple. Thanks for the great info, atleast now, I've got a better picture of what happening. You don't think I'll need a new tansmission or anything like that? Really its just a matter of getting the valve checked/fixed/replaced right?

 

[tomhaney1]

IMO, I would also get the torque converter replaced to be on the safe side. They may also recommend a rebuild for the transmission but don't do it. Get a remanufactured one from a place like Phoenix Hard Parts, or the like. It may cost more initially but you, and your wallet, will thank you in the end!

 

[JP4RNR]

I had this same situation and in my case even after changing the torque converter I still had the issue with the torque converter not locking up and strange erratic shift patterns when the trans was hot. My transmission was overhauled and I still had issues. What I learned is that most trans overhauls only include "soft parts" seals, clutches,gaskets etc. It wasn't until I replaced my valve body with a rebuilt unit that my issues were completely resolved

 

[CrazyMofo]

I had this same situation and in my case even after changing the torque converter I still had the issue with the torque converter not locking up and strange erratic shift patterns when the trans was hot. My transmission was overhauled and I still had issues. What I learned is that most trans overhauls only include "soft parts" seals, clutches,gaskets etc. It wasn't until I replaced my valve body with a rebuilt unit that my issues were completely resolved

Do you have a rough guesstimate on how much this will run me?

 

[tomhaney1]

I had this same situation and in my case even after changing the torque converter I still had the issue with the torque converter not locking up and strange erratic shift patterns when the trans was hot. My transmission was overhauled and I still had issues. What I learned is that most trans overhauls only include "soft parts" seals, clutches,gaskets etc. It wasn't until I replaced my valve body with a rebuilt unit that my issues were completely resolved

I guess I am confused as well. They replaced the valve body when I had the new transmission put in. Is this not the standard procedure?

 

[JP4RNR]

Only hard parts are replaced if needed and you are charged accordingly. Soft-part overhaul would probably run 1700- 2K

 

[CrazyMofo]

Okay, I better start putting in some more OT.

 

[tomhaney1]

Only hard parts are replaced if needed and you are charged accordingly. Soft-part overhaul would probably run 1700- 2K

Ah...Do you think that is the difference between a completely remanufactured transmission and a simple rebuild? That is what I take it to mean. IMO, that is the way to go, a reman. over a rebuild.