No worries, appreciate the response anyway!
I have found quite a lot of info for US owners with this exact issue, know as "acceleration hesitation" including many fixes, but have found very little from UK owners who have fixed this issue. I am determined to see this through and fix it so will post any updates here for future UK owners. Please excuse the long post but I want to include others with as much info as I can.
So the issue on mine is exactly as described by Ross in their original post. My car is a 2006 LS460 with 101k miles, recent Lexus main dealer service history.
My car experiences the issue, however after a few miles of constant 60mph+ driving, i.e. motorway, the issue completely goes away. After a few miles of slow town driving, it returns. No exceptions to this rule. Sometimes there is an "inbetween" stage where if the acceleration is lagging I can come off the throttle, then back onto it and the car flies. But this never lasts long. Manual or auto mode does not change anything.
Where it started: my car was with Lexus Bristol for a gearbox oil and brake fluid flush & replacement. Engine oil service had been done a few months prior. Drove fine for 2 weeks and then this issue started, not sure if it is related to the service undertaken. Curiously, my airbag light (passenger knee) came on the same morning the issue started. No idea if related but maybe worth noting.
I've lived with it for a few months as I mainly do motorway driving. In that time I have tried some of the quicker/easier potential fixes found online: using all different brand and grade of fuels, using BG 44K fuel system cleaner, using PWR mode. No fix.
Last week, upon accelerating from a stop at around 10mph/2000rpm the engine coughed and stalled. Orange CEL, VSC, PSC and red battery lights flashed. Started right back up (Same lights illuminated minus battery light) no issues and drove as before. OK, it was time to return to Lexus. A day or so before it went in, all the lights did disappear but the computer stores these codes.
They scanned the computer and found a few codes, most pertinent was P2119 for 'Throttle Actuator Control Throttle Body Range/Performance'. They took out the TB and cleaned it up, test drove and none of the codes returned. Even the airbag light went and has stayed out. So some progress, but the car still drove like a pig around town so no dice.
My next two avenues of approach are:
1) Check that the Valve Spring Replacement recall described here: https://media.lexus.co.uk/lexus-announces-uk-recall-campaign/ has been performed for my car. Many US owners report that this fixes the hesitation issue. Lexus did issue affected VIN#'s for US cars but I couldn't find any for the UK, however my car definitely fits the correct age range. I don't honestly think this is the issue but I have asked Lexus to confirm if my car was affected and/or repaired under this recall just to cross it off the list.
2) Secondly, and far more promising, is that many US owners report that a technical service bulletin to update the ECM/Powertrain Control Module parameters completely fixes this issue. These are 2008 L-SB-033-08, later superceded in 2017 by L-SB-0122-17. I have attached pdf copies of both, and they exactly describe the issue our cars have experienced. Funnily enough, they also make reference to the fact that the car may throw a check engine code... you guessed it P2119 for Throttle Body! This TSB involves a reflash of the ECM/PCM (sometimes multiple reflashes required), and in "some cases" replacement of the heads. Ouch. Unfortunately these are US-based bulletins and do not apply in the UK. I have sent this information to Lexus Bristol and I am hoping that there is a UK equivalent, or at least an ability to perform the same update to my car. If they can't or aren't willing, I will explore whether any good Lexus indies are able to do this.
There are a few further fixes I have identified through my research, including Peter's excellent info earlier in this post, however for now I'm cautiously optimistic on the above TSB.
I will post again when I have a meaningful update.
L-SB-0122-17 'Hesitation on Acceleration and-or P2119' [2017-05-03].pdf lsb003308.pdf
