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High rev but no acceleration

I am driving a 1987 mk3 Toyota supra with original engine and transmission. I live in Arizona and it drives perfectly fine in the early morning or late at night, but during the day when temperatures reach past 90°, my rpms will reach up to 5-7000, but won’t be gaining speed, thus happens at stops and while driving, my car is an automatic, it does this when I enter 3rd gear. Any help appreciated

The first step is to check the level, color, and odor of the trans fluid.
It should be a reddish-pink in color and it should NOT have a burnt odor.
If the fluid is low, replenish it with the same type of fluid specified in your Owner’s Manual, and see if it accelerates normally after that. I’m not optimistic that it will, but…

If the fluid is dark brownish/black in color, or if it has a burnt smell, the car needs to be taken to an independent trans shop a.s.a.p. Whatever you do, do NOT go to AAMCO, Lee Myles, Cottman, Mr. Transmission, or any other chain-run shop unless you want to overpay for substandard workmanship.

I think that you are going to need a transmission shop, one way or another, but it is worthwhile to do the fluid check that I mentioned, just in case it does help.

Start simple, trans fluid and filter change.

Yeah. Get that fluid changed immediately.And all the above advice is excellent. From persomal experience I can say that both those chain shops have overstated the needed repairs, charged for the repairs that were quoted yet only made the minor repairs that were actually needed.

It’s a shame that car owners are so often victims of the unscrupulous or the incompetent.

I think your transmission is over heating. There should be a transmission oil cooler, but it might not be working. Check to be sure the lines to the cooler are clean and clear. The cooler itself could be gunked up ineffective. When you’re sure the tranny cooler is good refill with fresh fluild and see what happens.

…rpms will reach up to 5-7000, but won’t be gaining speed, thus happens at stops and while driving, my car is an automatic, it does this when I enter 3rd gear.

If it’s a 3rd gear issue, what do you mean happens at stops?

Sorry I meant that my rpms can reach that high directly after a stop, or in the middle of a drive

When the engine revs higher but the vehicle isn’t accelerating something is slipping and it is quite likely that it is a clutch set which is quickly becoming sludge in the bottom of the transmission pan. And once a clutch set is wiped out the transmission will need to be rebuilt. Low fluid level, high fluid level, sludge blocking the pump pickup or ports in the valve body will cause clutches to slip. “Drive it like you stole it,” i.e., continuing to drive, will almost certainly be a costly mistake. If the vehicle is taken in for service before it is too late it would be wise to make certain that the shop uses a flush agent on the transmission cooler.

Would replacing the whole transmission fix the

It’s a lead pipe cinch that replacing the transmission will correct the problem. Flushing the cooling system is critical then also.

“Would replacing the whole transmission fix the problem” (?)

Of course it would.
Did that suggestion come from somebody at AAMCO?

It definitely sounds like slipping clutch packs in the automatic transmission. Yes, automatics have clutches too, and when those wear out, this is the result. When my Ford C4 automatic had that symptom, it was in the shop shortly thereafter for a complete transmission rebuild, which fixed the symptom straight away. You could get lucky tho, just a proper transmission service might fix it, that’s the place to start.

The car is 29 years old…It is likely it’s not worth the price of a new transmission…

I think a 1987 Toyota Supra may have some classic potential. Especially if not ravaged by rust and it has been kept close to stock.