autoxtraz

Master mechanic well puzzled.....Well folks after reading every possible thread re GS rough idle/misfire for 3 years we are still no wiser.....2003/3 model 300 also runs with LPG which helped to eliminate some possible causes as we can switch on and off. The rough idle is approx 50-100rpm - small but very very unsettleing as it started a year after we bough the car. We have been to Lexus - only showing same codes our reader does 300/301/2 and sometime 4/5 and generic misfire - techy stated yes we can hear its running off but dont know why - pay us anyway!. Recently in last month changed all these and ran car for 5 days in between each change of part with no difference: Coil packs, Plug lead, 2 x sets plugs, maf, full set of injectors - timing is spot on and has not been touched, whole of intake system been taken off and cleaned and when running every possible air lead area has been sprayed with carb cleaner to find leaks but none were found. When we switch to LPG the misfire gets amplified to a 200-350rpm difference. Which would seen to suggest either mechanical or electrical not on fuel side.
Oxy sensor B2S2 was changed few years past but no fault codes appear on that matter - but I believe this is only a heater anway?
Other than the above the car is stock.
ANY ideas anybody????? must be some as it appears every damn Lexus suffers from it....
HELP Pls folks

Mr Jokster

iTrader: (8)

VVT-I Controller or sensor?

GS4_Fiend

iTrader: (22)

What are the vacuum readings when the car is misfiring? Perform a relative compression test.

sam12345

iTrader: (1)

Ecu? ...... ......

autoxtraz

Well the saga continues - we have borrowed another cylinder leak tester - not Chinese this time.... and got a shock - cyl 1 100%, cyl 2 90%, cyl 5/6 80%, cyl 4 70% but cyl 3....15-80% !!! and these reading changed considerably over 3 tests - so next step. We are going to run a few tanks of gas (not lpg) through the system with some additives and hopefully will clear and carbon deposits on the valves and intake system - with any luck will rectify the leakage - otherwise it's head off time...will let you guys know how we get on.
NB above tickover the car still drives perfectly albeit a little bit down on power.

powerjunky

iTrader: (2)

2nd on ECU....i bet it has leaing capacitors

id swap with a buddies known woring before you do anything else

eeric7

Ecu can cause misfire? ,I've swapped everything that can cause misfires on my car spark plugs ,spark wires ,ignition coils ,fuel injectors are good ,compression is good ,