Lexus IS250 and GS300 rough idle and/or P0301, P0302, P0303, P0304, P0305, P0306

CARspec now offers walnut shell blasting of the intake valves to help prevent this issue!

2006+ IS250 and GS300 owners are frequently concerned over a rough idle, especially after sustained freeway driving, or a check engine light with codes P0301, P0302, P0303, P0304, P0305, and/or P0306 (misfire codes).  The idle can often cause the car to stall and the check engine light to flash, but is intermittent in nature and can fool even the most seasoned auto mechanic.  So what the story here with the problem and what should an owner do?

The problem lay in the design of the engine, specifically the shortcomings of the direct injection system.  Because the fuel injectors have been moved from the intake tract leading into the engine (upstream of the intake valves) into the combustion chamber, the fuel mixture no longer cleans the intake valves of harmful carbon deposits.  While moving the injectors into the combustion chamber improved fuel economy and power, the lack of cleaning leads to buildup.  This buildup eventually breaks off and is ingested into the engine causing the intake and exhaust valve to hang open (causing a partial misfire) or damage to pistons, rings and cylinder walls.

IS250 and GS300 direct injection engines benefit heavily from regular induction services to help dissolve these intake valve deposits.  You can read more about that process here.  Regular oil changes and the occasionally going full throttle (where safe) has also helped owners prevent the condition.

How can you tell if you have the issue?  Before you take your vehicle to your local Lexus mechanic, try duplicating the concern by:

• Let the vehicle sit for an extended period of time, preferable overnight.
• In a well ventilated area, start the car and let it warm up to operating temperature.  Let the car run for several minutes until the heat from the vents is hot.  Note any hiccups or bumps in the seat – these may indicate the condition.
• Rev the engine in park to 4000RPM for 30 seconds.
• After 30 seconds at 4000RPM, bump the revs a bit higher and let them fall back to idle.
• Note any rough running or misfiring.  If you have a scantool or code reader look out for codes P0301, P0302, P0303, P0304, P0305, or P0306 indicating a misfire on the respective cylinder.
• Repeat the process of revving the engine for 30 seconds, bumping it up a bit, and then monitoring 10 total times.  If the engine runs rough, stalls or sets the check engine light you likely have the condition severe enough to warrant repair.

Alternately, if the above doesn’t duplicate the concern for you try the following:

• Let the vehicle come to temperature until the heat from the vent is hot.
• Drive the vehicle under a steady load at a stable speed in a lower gear, keeping revs above 3.5k for a few miles.  CARspec drives the car in 3rd or 4th gear at 60MPH.  Make sure to monitor engine temperature and behavior as you would normally when driving.
• Pull the vehicle over where safe, put the vehicle in neutral and rev the engine once to redline, letting it fall back to idle.
• Monitor the engine for rough running or a check engine light as it idles.

As a Lexus specialist we’ve found the top procedure (as dictated by Lexus) works the best but sometimes leaves a bit on the table, and hence the second procedure.

Fortunately for owners Lexus extended the warranty for this specific issue, to 9 years with no mileage limit as part of campaign ZLA.  They will repair your Lexus with either new pistons and rings (IS250) or by cleaning the pistons and replacing the rings (GS300).  They have strict duplication criteria and repair is at the behest of Lexus repair’s corporate HQ, so don’t expect every little hiccup to come with a new engine.

For those unfortunate enough to have the condition and are out of warranty, CARspec offers an alternative repair for owner not willing to rebuild their engine without first exhausting all options – a top engine clean of the pistons, rings and intake valves in conjunction with an induction service.  Following Lexus repair bulletin L-SB-0029-10, the intake manifold is removed, the cylinders filled with a small amount of special GM top engine cleaning product, and the cylinders allowed to soak before the engine is reassembled and test driven.  This can smooth over the misfire and rough run concerns of owners.  As Eden Prairie and Chanhassen’s Lexus repair specialist we’re happy to offer this service many an auto mechanic would scratch their heads over.