So I've had some ongoing issues with my trunk as it doesn't seem to pop open itself when it unlocks, instead the lock just cycles twice and the trunk will not pop open without me manually trying to lift the lid.
Essentially, I'm having the exact same issue as the OP of this post (although their problem is on a BMW).

I've checked the actuator and the striker and it seems like they're both fine; as the trunk lid has been replaced before and the trunk struts seem to be aftermarket, I suspect those are the culprit, though I'm not 100% certain. So for those of you who have a working trunk release, I'd like to ask:
1. Are your OEM hydraulic struts pressurized enough to be able to pop the trunk open on its own when you unlock the trunk?
2. Does your lock actuator also cycle twice when you unlock the trunk (via the keyfob, smart key button or cabin switch)?

Hopefully some of you can answer my question so I can figure out exactly which part is wrong and what to replace. Not very fun to order parts online just to find out they don't solve the problem...

 

I need new struts too. From what I recall, they pop up a bit when good, but not a huge amount. Mie also dont hold well open either, a sign they are worn. I've gone through 2 hood strut sets. I used nn-OEM for those and they were fine for last 7-8 years, but no longer. For trunk, I'd go OE, as I want it to work just right. I don't think they are that expensive online.

 

The tunk on my LS430 just barely pops open, I replaced the struts with no noticeable change. There is a rear spoiler on the trunk lid so that may be why the trunk doesn't pop open.

 

My trunk works normally. ('05)
1. Are your OEM hydraulic struts pressurized enough to be able to pop the trunk open on its own when you unlock the trunk? Yes, just barely but enough/
2. Does your lock actuator also cycle twice when you unlock the trunk (via the keyfob, smart key button or cabin switch)? no

 

Alright, it seems that my struts are indeed not providing enough pressure to pop the trunk based on everyone's feedback. I will purchase some OEM struts and report back if it fixes the problem.
Here's a video I took of the trunk actuator in action. Seems like it "cycling twice" is just the motor unlocking the lock pin and moving the actuator back in place, so it should be working fine.
I think what's happening is that the actuator moves the lock pin to the open position, but since the struts aren't strong enough to lift the lid, the lock pin essentially never leaves the top of the striker hook and it "falls down" and locks itself again as a result. Must explain why I can hear motor noises whenever I press the unlock button, but the trunk never unlocks unless I lift it manually when the actuator is cycling.

 

"I think what's happening is that the actuator moves the lock pin to the open position, but since the struts aren't strong enough to lift the lid, the lock pin essentially never leaves the top of the striker hook and it "falls down" and locks itself again as a result. Must explain why I can hear motor noises whenever I press the unlock button, but the trunk never unlocks unless I lift it manually when the actuator is cycling."

I think that is exactly correct. Your new struts should prevent that from happening. I think my struts are still original. Same with hood shocks. Definitely OEM is the way to go on these.

 

I replaced my rear trunk supports about a year ago. My 2005's trunk, once released via the keyfob button or interior, would unlatch and maybe rise up about an inch. Keep in mind it had done that since I bought it in 2009 when it had about 40k miles. The reason I replaced the supports was because I had to lift up with tremendous force to raise the trunk lid. Once open, it was fine, and stayed open, unless it was really windy. A strong wind could knock down my open trunk quite easily.

I bought aftermarket from Rockauto, took about 20 mins to replace them, and haven't looked back.

The trunk opens exactly how it did in 2009, except now, after I raise the lid several inches, the supports push open the lid with authority! and keep it open! With my old supports, I had to nearly lift the trunk lid, all the way to the open position, and hope the wind didn't blow suddenly!

The trunk lid DOES NOT rise open all the way, automatically, similar to how a 1978 Oldsmobile did. EVEN WITH OEM SUPPORTS, YOU WILL BE USING YOUR HAND TO LIFT THE TRUNK OPEN, THEN THE SUPPORTS WILL TAKE OVER AND RAISE IT.

I literally did my hood supports last weekend, and no longer have to place a 2x4 piece of wood to hold the hood open. A simple fix like this is SO rewarding. By the way, unfortunately, my supports were made in China. I was able to peel off the sticker and the support is simply all black paint.

 

What @LS430inDE. said.
Keep in mind this car does not have the auto-open or auto-close. The trunk release will just pop the lock and raise it maybe a half inch, and then you have to lift the trunk. Upon closing, you have to gently lower the trunk lid, and then the pneumatic soft-close will pull down another half inch. I have confirmed this with new struts and there are other threads on here confirming this.

 

The reason it is designed this way is if trunk button on fob pushed by mistake the trunk will auto close after set time if not opened just like the doors. I have seen cars with trunk open and nobody around which most likely opened by mistake.

 

Agreed the trunk is not designed to pop open. My BMW is a 2007 purchased new and it does not pop open. It does have this strut design that allows for the elimination of arms whereby increasing the capacity. One flaw of the LS430 is there is only a handle on the right side. I normally approach from the left and back into a parking space without space to walk behind

 

I have 1 time almost got my finger stuck with the auto close as I was pulling from bottom and slipped a little and closed. Luckily I jerked my finger out and almost lost a nail.

 

Yes, and I hate it. I understand why, but I dont have to like it. If the Lexus has one fault, this is it. I have thought of adding a spring assist to give it a real pop.

 

New struts apparently did not fix the issue.
The trunk now pops up a bit further when I unlock it but still gets pulled back down into the striker hook by the motor just before the actuator latch can clear the striker... This almost feels like the soft close system has gone wrong and is actively pulling the trunk DOWN when I try to unlock it. Seems like there is actually something wrong with the electronics somewhere.
Currently reading the systems description page of the repair manual in hopes to learn more about the issue. Unfortunately I don't live anywhere near a junkyard with an LS430 that has a working trunk mechanism that I can salvage parts off of...

 

There are quite a few for sale on eBay ~ $70 - $75

 

Unfortunately I live in a region where buying from most ebay sellers (based in North America) would be cost-ineffective as shipping prices are just too high. I did order a couple of actuators from different junkyards in my country but none fixed my issue, and I had to return them all
Plus, I'm not even sure that the actuator is the actual part at fault. Just by reading the repair manual, it looks like there's multiple components controlling how the actuator motor works, so I can't get the full picture without going to look at a functioning example in person unfortunately