Dashpot Problem Causing High Tickover

[Guest Roger NE]

Just fitted a new 2JZ-GE Engine in my Mk3 Supra . . . and the tickover is around 1500 RPM

 

But I've discovered it's just the Dashpot, as if you push it right in, the tickover drops to a perfect 700 RPM. But as soon as you open the throttle again, the tickover is high, as the Dashpot doesn't go back on its own.

 

However . . I don't really understand how it works, as it's quite different from the Dashpot on my previous Mk3 engine . . difficult to see it, and the TSRM is very vague and has no clear diagram . .

 

It's as if it's sticking, not going right in on its own, unless you put your hand on it and push it right home. Any tips on freeing up this Dashpot would be appreciated . . . can't really see what exactly it does, so even an explanation would help.

 

On my old engine, a 7M-GE, the dashpot is just a simple damper that the throttle lever hits just before it closes the flap fully, and slows down the last little bit (presumably to stop too much back pressure on deceleration)

 

But it seems rather different on the 2JZ, as if it is actually attached to the throttle flap itself. (as I say, can't actually see it properly on the car, and can't find a clear diagram)

 

I don't think it's an adjustment issue, as if I push it, the throttle flap then closes fully . . . it seems to be sticking. But even though the throttle pulleys have gone fully back, they don't push the dashpot fully home. (it seems as if it's supposed to go back on its own . . . but it doesn't !)

 

Hope someone can advise ! (Originally raised this issue on my New Engine thread . . . but have re-posted, as had no useful replies)

Edited January 10, 2014 by Roger NE (see edit history)

[Guest Roger NE]

Wish somebody could help with this !

 

Tried adjusting the backstops on the throttle cable pulleys this morning to see if that would help . . . but both are seized solid! (the Allen Key hole on both just snapped off the bottom . . and can't turn them with a small Mole Wrench)

 

However, presumably they were in the right place originally, and worked OK.

 

I notice these engines have TWO Throttle Pulleys, an extra one for the Cruise Control. However, on the Mk3 the Cruise Actuator pulls the actual Accelerator Pedal under the dash, so you only need the main Throttle Cable.

 

Not sure which the Mk4 uses for each, but I've attached my Throttle Cable to the Pulley towards the rear of the engine, as the other one has too small a hole for the trunion on the end of the cable . . but can't see that would make any difference?

Edited January 11, 2014 by Roger NE (see edit history)

[Swampy442]

Can you not remove the dashpot and see if that stops the problem? Im pretty sure Ive got an NA throttle body complete in my garage somewhere. If I can find it you're welcome to any bits you want.

[Guest Roger NE]

I'm trying to avoid dismantling stuff to take the Throttle Body off . . . that's what I'd have to do to see how the linkages and levers work (or remove the Dash Pot), as it's impossible to see on the engine

 

I'm hoping someone can explain how exactly it works, as it seems quite different to the Mk3 engine

 

If I had an idea how it works, I might be able to sort the problem in situ !

 

It seems as if the Dashpot has a rod sticking out which is connected directly to the lever which operates the Throttle Flap . . . so perhaps the flange on the Throttle Pulleys are supposed to push this back when they close fully? (whereas at present they don't . . . I can push the rod underneath back by hand, and then the tickover is normal.

[Swampy442]

Its just a damper, thats all. I looked on Toyodiy and the part numbers between GE and GTE so don't know if its the same item but Ive got an Aristo outside, could get a pic tomorrow if you want. But yes when the throttle is closed the arm should be compressing the dash pot in.

Also you're right about the 2 pulleys, 1 is for the cruise and the other for the pedal. Have you got any tension on the throttle cable?

[Guest Roger NE]

No I've made sure the throttle cable is slacked off . .

 

So which pulley is normally for the Throttle Cable? (and wonder if it makes any difference which one you use - I notice they seem to work independently, not together)

 

I gather the rod coming out the damper can be adjusted in and out (as I say, it's almost impossible to see it on the car)

 

If so, maybe it needs extending so it is pushed right in by the lever from the pulley? Because even though there seems to be a gap at the end of it, when I push it in the tickover drops to normal . . . as if it is connected directly to the actual throttle flap lever.

 

Just had a look at the Parts Diagram on Toyo DIY . . . but it is no clearer than the TSRM !

 

I'd really like a diagram looking at that side of the throttle body, so I can see how it all links together !

Edited January 11, 2014 by Roger NE (see edit history)

[Swampy442]

These picures are from a GTE equipped Aristo, so Im not sure they'll be any help.... But the throttle cable normally attaches to the pulley closest to the throttle body.

 

 

 

[Guest Roger NE]

Many Thanks for posting those photos . . .

 

However, it looks like your Dashpot is the other side of the Throttle Body from the throttle cable pulleys . . .

 

Whereas on the Supra 2JZ-GE engine it's underneath the pulleys . . . that's why it's really difficult to see what's going on !

[Guest Roger NE]

Still hoping somebody can advise about this !

[LOGIE]

Roger the 2jz na engine when mated to an autobox uses another throttle cable which is connected directly to the autobox itself.

[LOGIE]

[LOGIE]

[Guest Roger NE]

Roger the 2jz na engine when mated to an autobox uses another throttle cable which is connected directly to the autobox itself

 

Not sure how that affects my problem?

 

And I thought the second Throttle Pulley was for the Cruise Control ? (and this engine was from a MANUAL car anyway)

[LOGIE]

Not sure how that affects my problem?

 

And I thought the second Throttle Pulley was for the Cruise Control ? (and this engine was from a MANUAL car anyway)

 

Ah right. Yeah the cruise control is next to the throttle cable but there is another pulley for auto throttle control.

[Guest Roger NE]

Bizarre that the Mk4 has all those separate cables to the Throttle Body (messy!)

 

On the Mk3 there's only ONE . . . the Cruise Control and Auto Kickdown all work from the Accelerator Pedal under the lower Dash. (seems a much neater way of doing it . . . and makes Engine Swaps much simpler)

 

ANYWAY . . ended up taking the Throttle Body off so I could see properly how it's all supposed to work.

 

All the adjustment screws had been sealed with paint, which is why I couldn't budge them.

 

The whole mechanism was slightly fouled up . . . so cleaned it all up and adjusted it properly.

 

So it's all OK now . . . . normal tickover !

Edited January 12, 2014 by Roger NE (see edit history)

[Swampy442]

Result!

[herbiemercman]

Result!

 

Hi roger, thankyou for this and your other thread re the problems of tickover my car which i have owned from new is a mk4 manual and has only covered 45,000 miles, has started ticking over circa 400 rpm it only just keeps running, and now it has started ticking over at 1,200 rpm. So your thread is just what i wanted. I will start by checking the mechanical items, then cleaning etc, hoping it is not and electrical problem as in the absence of any diagnostic software you end up changing parts, expensive and frustrating. I have diagnostics for my merc and i am a friend of chris wilson the supra wiz, i met him last year when i towed my brother's tt down to his clinic. herbiemercman.

[Guest Roger NE]

Bear in mind that the small adjustment screws (with holes in the end for a tiny Allen Key) are held in position by a locking nut - you need to loosen that before you can adjust anything.

 

The problem is that it's really hard to see how the setup works whilst it's on the car . . . not helped by the lack of any proper diagrams in the Toyota Service & Repair Manual.

[herbiemercman]

Hi Roger, could you tell me what the components are and where they are located. ISCV ? TPS ? CPS ? dashpot ? oil breather valve ? My car is a 1996 mk4 manual. Any help will be appreciated. herbiemercman.

 

 

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[Guest Roger NE]

You really need to look at the Repair Manual (TSRM) - I think there's a link to an online version if you Search on here

[herbiemercman]

Yes i will look up for the TSRM, i will also investigate somthing i read in another thread where a guy had the tickover problem and rectified it by re-connecting the wire from his de-restrictor / kph.mph converter unit to the appropriate connection on the ECU. My converter unit failed some months back and this is why i am suspiciouse of this possible failure mode. I will post my findings for the benefits of other members. thanks again for your reply. herbiemercman.