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The mkiv Supra Owners Club

Throttle Position Sensor (TPS) intermittent harsh gear changes and idle problems


TubbyTwo

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Dude, I get about 250 miles to a full tank with normal driving as well! If you define a full tank as "the light has started to come on", and normal driving = a lot of city stuff. With an iffy autobox and the cold weather causing more accessory use and extended cold start etc. this is to be expected.

 

You can check your O2 sensor at warm idle with a multimeter to see if it's okay anyway :)

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Thinking about this I've doe a few searches of t'net and dug up this nice troubleshooting guide for Toyota autoboxes (yours is an A340 by the way). There is a bit about fault code checking on page 12 (section 5), so do that first if you haven't already, but what was rather interesting is on page 16 - the Manual shift test.

 

You unplug a solenoid connector (there is a picture showing where it is, good luck relating that to the real thing because I couldn't) and then the transmission won't shift unless you move the stick manually. The great thing about that is position 1 = 1st gear, but position 2 = 3rd gear, your troublesome one. So you can lock it into 3rd like this and do some testing :) You can also test overdrive by putting it in D.

 

So if 3rd works okay when it's manually locked in, it'll be an electrical issue. If it still struggles it's probably hydraulic.

 

The rest of this PDF has a bunch of other tests you can perform as well, but I'd start with that one :thumbs:

Autobox troubleshooting.pdf

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After more reading, it could be your C2 clutch (page 29) - I think you're experiencing slip when it changes to 3rd gear, which saps the acceleration away as the power is going towards heating up fluid/friction components instead. The video I took supports this and the behaviour in lower gears, as it rockets up to just over 3000rpm and stays there slipping while road speed catches up.

 

Locking it into 3rd at low rpms will be a good test of this, see if it slips up to 3000+rpm when you floor it, and compare that to 1st gear. You could also left foot brake to put more load on 1st gear to make it a better test.

 

Also, try getting up to about 4000rpm in 1st, holding it there with a steady throttle, and then shifting to 2 to put it into 3rd. It will probably take overly long to drop the revs down to 3rd gear's road speed if it's this clutch slipping.

 

Clutch C1 is used for 1st and 2nd, clutch C2 only comes into play for 3rd and overdrive, so this all fits. The change from 3rd to overdrive possibly won't slip though, as C2 is already fully engaged and isn't mucked about with.

Edited by Ian C (see edit history)
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wow, ok thanks Ian this weekends job, will try and get a friend to sit and film for comparisons.

 

On another note still running the new auto ecu the box now has a new trick from cold, when pulling up to a junction in 2nd, foot off the throttle and onto the brake the box was juddering in the change from 2nd to 1st. Such as a manual car if you try and pull away without enough revs. did this until the box warmed up.

 

will get on the error checking of my original ecu tomorrow.

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Swap back your old ECU and see if the juddering issue goes away again. Either it's an artefact of that ECU, or your autobox is starting to circle the drain and showing other symptoms. Also, make sure you get the issue a few times bafore checking for codes - unplugging the ECU is an efficient way of clearing any stored ones ;)

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  • 1 month later...

Long overdue update, the car is now terminal, driving home last night and went for an overtake just at normal speed, no kickdown or excessive boost and its finished the box off, now whines really loudly, even with normal fluid levels. :D

 

now struggles to idle in anything other than park, idle hunts all over the place, car slams into gear to the point where it jolts you back in the seat, even at low speed pulling away. The final nail in the coffin is the fact it stalls at junctions, checked fluid last night and its black, even after changing for some new halfords special to tide me over.

 

Booked in next week to be changed which has been arranged since before Christmas, was hoping it would last.

 

In park or N its fine, just when any other gear is engaged.

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