Gs300 No Power When Cold - Poss Iacv Or ?

[Jock666]

Old problem just got dangerously worse......

03 GS300, had this prob ongoing for years now a dangerous joke. Lucky car has LPG - so get to start it & let idle until warm & gas cuts in otherwise undriveable when cold.

On petrol when cold it does NOT stall or shudder at start - it starts perfect on choke, moves back/forward with power no problem. Get onto to road and ...NO throttle NO power just dies to idle appears to be in limp mode but even the little bit of wire left on throttle does nothing, then starts to hunt/drop revs etc. keep throttle pumping and after 3/5 mins it clears, gets full revs then is fine. By which point its switching to gas anyway. The EML will eventually come on only to say misfire. Not a single code from 5 different readers - including Lexus - has ever pulled a code for us.

What we did learn was that the TCT light is constantly activated by the YAW sensor - which even though got changed - still comes on so gets reset every week or so - the joys of Lexus ownership.

So - to the NO power problem - suggestions other than the usual rude ones I tell myself......

[ColinBarber]

What speed does it idle at when first started? Does having the A/C on help?

[steve2006]

Having LPG makes diagnosis more complicated but IIRC there is an emulator fitted which tricks the engine ECU into thinking the car is still running on petrol when actually running on LPG, again this is from memory but doesn't this same device or the LPG ECU also switch off the fuel injectors when on gas?

If a fault was to develop with these it could mean the fuel injectors are switched off when they should be on for petrol running.

All the other bits like the throttle body, TPS etc are common to both systems so unlikely to be the cause.

With the fault clearing after a few minutes may be worth checking temperature sensitive components like the Coolant Temperature Sensor.

[Jock666]

All of the LPG parts have been tested/serviced inc emu and replaced over last 4 years - been to 2 other garages for check over with no faults found. Runs perfect on gas after we got right plugs fitted. When warm on petrol never misses a beat. The NO power problem started off during normal driving cycles - even on motorway a few times and no manifested into cold start problem. The complete engine and injection system have all been changed to a 50k unit along with new injectors, 3 maf's, oxy sensors etc etc etc - lost count of the time and money spent, And that doesnt include the £3k spent on scanner equip....

Car starts perfect (except when Battery flat again afer few days....4 in 4 years) idle jumps to 1100 ish if memory serves. Can drive out the driveway for about 50/100 yds then NO power or throttle pedel - if left on petrol as stated takes a fair bit pumping (more of a placebo for my frustration & benefit than for the car!) until - feels like blocked fuel line - comes clear and takes rev.

BTW last week fitted complete fuel pump assy into the tank which was pristine inside as I was convinced the intank filter had clogged! - Nothing - no change at all.

[ColinBarber]

did it do this before you changed to the plugs you now use? Sounds like they might be fowling up when running on petrol with a cold engine running rich.

[Jock666]

Should mention only reason motor was changed was some *&(&^% in a very well known "specialist tuning shop" has it on the dyno & diag equip and stated "problem is without doubt cyls 2/3 have burned valves caused by lpg" - absolute boll*&^s! It was cheaper to pop in low mile motor than strip and redo head - but curiousity afer swap was finished......head was 100% perfect - even cc'd it and chambers were with 5% across all 6 cylinders @ 147k miles - and no leak through on valves sweet. Block was just like new. So - loads of dosh - time and aggrivation for nothing. Better still had the UK No1 trouble shooter for Denso here - what a dissapointment!!! big titles little sense.

[Jock666]

Ref plugs - went through 4 sets diff heat before found perfect ones - car had done 80k on gas before we bought it and was fine at time of purch - prob was never on petrol though and this definetly isnt plug related. Misfire caused by lack of fuel or mixture.

[ColinBarber]

I'd like to think that somebody has put a data logger on the vehicle to monitor all the sensor to see if something misbehaves when the issue occurs?

To answer your IACV question, it shouldn't be related to that, it doesn't make that much of a difference. The ACIS system should only operate with a throttle angle of 30 deg or more so it is was the problem coming off the throttle would resolve the issue.

[Jock666]

The data logger facility on our new Autel DS708 only sends the file automatically back to the US factory for later updates on their software - so no we do not have access to a data log file here. The machine was again updated today and no fault code other than usual misfire recorded. So will have to assume nothing untoward is showing to the techies.

[ColinBarber]

many obdii tools and programs allow multiple sensors to be continuously polled, either plotting the results on graphs or logging the data values to a file. That way you can able to go back over the data and look at the point where the issue started to see which sensors suddenly changed their value and work out which one was the trigger.

For example, question 3 at the following link shows the results taken from 8 points in time, at frame -5 you can see the Throttle position sensor value suddenly change, which triggers an issue resulting in other values also altering:

http://www.autoshop101.com/tests/intest14.html

In addition to the sensors they show in the example above you can log many more including duty cycle of injectors and O2 sensors etc. Results may not pinpoint the fault but could at least point you in the right direction.