1HD-T idle drop when facing upwards-FIXED (1 Viewer)

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Several 80 series have reported an annoying problem, including mine: When facing steep uphill slopes the idle drops from the recommended 750rpm to about 400 rpm. This has been discussed several times in the forum. Pusher pumps do not seem to fix the problem, and so far people just decided to live with it.

On my truck a similar thing happened when I decided to just idle along without using the accelerator-idle dropped to 400rpm, quite annoying.

After reading up on the intricacies of these pumps I thought the so called damper spring could be the culprit. This spring senses increased load at idle and up-regulates the fuel flow slightly in response.

The damper spring is located in the head of the pump, you can find it in the 1HD-T manual on page FU-31. There is a spring system that connects the speed control lever/adjusting lever with the fuel control system in the bottom of the pump. The speed control hooks to the adjusting lever, this to the speed control spring, which is hooked to a spring seat that also contains the damper spring. If you look at the pic below it will all become clear.

I decided to change the damper spring, the spring seat, the speed control spring and of course the gasket for the head of the pump. While I had my pump fully rebuilt, these parts are toyota specific and were clearly not swapped out during the rebuild.

The procedure is not too hard: Take the fuel lines off the head of the pump, take the A/C idle up off, remove the low and high idle screws, and then carefully remove the 4 bolts that hold the head of the pump. Fuel will pour out, but after that you can carefully tilt the head of the pump forward. Remember that the head and bottom of the pump are hooked together with the speed control spring. You have to unhook this spring from the spring seat to remove the head completely. The manual describes the procedure more accurately. Make sure the spring seat and damper spring don't fall into the pump at this point! It is not required to remove the adjusting lever.
Then change the springs, the gasket, carefully re-hook the speed control spring to the newly placed spring seat and re-seat the pump head. That is a bit of a pain, since the spring loaded idle up system needs to be in the exactly correct position to seat the pump head correctly. But definitely doable with some playing and cursing.
Then bolt the system back together, hook everything up, and your problem has been solved.

I do not see the idle drop at inclines anymore, and when I just use the idle to go forward, it re-adjusts to around 700, just as it should.

Hope that helps someone in the future. Below is the page out of the manual that shows the springs, and all the parts that you need. I got them out of europe from my brother via Toyota Austria, but I am sure you can get them in Australia or Japan as well. The seal and the spring seat is actually available from Toyota USA via Toyota parts zone.
I bought 3 sets and we will keep one set at the shop as spares. So one set is available. While the springs are only a few $ each, I am asking $40 for the set (speed control spring, spring seat, damper spring and gasket) plus shipping, as we paid lots in shipping. If you need these and find the price outrageous, I understand. Please get your own, the numbers are below. Or I would exchange the set for an OEM hand throttle assembly, as sold by Akella.

Cheers,
Jan
springs.jpg
 

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Well done Jan.

Good information and data to have available.

gb
 
great info .. you din't take pics during your procedure ? any tip .?

No pics-2 hands were required all the time. But the manual has the procedure of taking the pump head in it, it really is not complicated. The hardest part is seating the head correctly when re-installing, but even that is self explanatory, as it only goes on one way.
cheers,
Jan
 
Good tech. Any theories on why the other rotary pumps dont die off at idle?
 
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Good tech. Any theories on why the other rotary pumps dont die off at idle?

The damper spring on the 1HZ has a different part number, so does the speed control spring. Maybe there is something in the iHDT spring ratio that makes the damper spring wear out faster.
I do not know exactly.
cheers,
J
 
I don't wheel but when and if I get around to it... Ill keep this in mind, thanks for the research!

Cheers!
 
Yeah, I have been suffering with idle issues when climbing obstacles, but even when it warms up enough it will start hunting at idle on flat surfaces too when your stopped at a light. I'm hoping this will solve these issues thanks for posting.
 
Thank God someone was able to do something about it! I hope this fix works on mine too.
 
Update: No problems anymore since changing the springs. End of June/beginning of July will tell, as we'll make an extensive Baja trip with lots of steep inclines, sand and idling. Hopefully it's a permanent fix.
cheers,
jan
 
Thats quite an accomplishement :hatsoff: Ive seen a few owners pull their hair out over this problem,spending big money,sometimes for entire pump rebuilds to no avail.
I guess we now know their diesel techs were fakes,incompetant or downright dishonest.

With your permission Im going to ask the mods to make this one a sticky;)
 
Thats quite an accomplishement :hatsoff: Ive seen a few owners pull their hair out over this problem,spending big money,sometimes for entire pump rebuilds to no avail.
I guess we now know their diesel techs were fakes,incompetant or downright dishonest.

With your permission Im going to ask the mods to make this one a sticky;)

No problem.

I have not yet decided whether to label rebuilders that don't address this as incompetent-I am on the fence. The pump manual does not call these springs a 'replace-item'...
cheers,
jan
 
No problem.

I have not yet decided whether to label rebuilders that don't address this as incompetent-I am on the fence. The pump manual does not call these springs a 'replace-item'...
cheers,
jan

Maybe I should have thrown "inexperienced" in then,Ive long suspected it was in that area and I have no training.

In the UK,they often want to fit a new pump when any problem presents itself.
One owner paid for brand new pump on a 1HD FTE after 12 months of the engine cutting out only to find a loose wire in the harness was the problem.

I asked a local pump rebuilder 4-5 years ago about this problem and got silence. I wasnt sure whether he didnt hear me or was keeping his knowledge close to his chest.
 
I'm now wondering if this is happening to my 1HDT?

In P or N it idles fine but when in R or D it is idling rough (almost like its reving below 4-500rpm). Can't tell you the revs as the tach does not work but as soon as i get the revs up she runs like a dream.
 
I'm now wondering if this is happening to my 1HDT?

In P or N it idles fine but when in R or D it is idling rough (almost like its reving below 4-500rpm). Can't tell you the revs as the tach does not work but as soon as i get the revs up she runs like a dream.

Maybe your idle speed is too low.Its normal for rpms to drop when you put into gear as you are puting a load onto the engine.
I have mine idling at 850-900,keeps the alternator and power steering happy.

The problem in this post is from when 1HD T are left idling with the nose facing uphill.
 
How fortuitous, I'm having the same trouble with my 13B-T. It will idle and drive fine until I come to rest on an incline - then the idle drops and I have to use the hand throttle.

Could it be the same fix as your 1HD-T?

EDIT: Idle is usually at 800rpm but drops to 500rpm on an incline.
 
The 1HD T pump is a rotary pump and yours is an inline pump,so they dont have much in common .
Ive never heard of it on a inline pump before.
 
Hmmmm.. :hmm:
 
Pulling up an old thread but does anyone know a source for these parts in North America? I tried my usual suspects but no dice...
 

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