Shaka_rob

I have an ES 300 1998 with 84,000 miles. For last 2 years I have experienced a rough idle on my way home from work or after about 20 minutes of driving. Funny thing is, it would always happen at the same place before getting off exit for home in middle of island Oahu in Hawaii. You could feel the car jerk (thought it was the awesome road system here) so when I slowed, the engine ran erratic 300-700 rpm. Now, if I gas it, rev up to 5k, it goes away, returning after about 10 minutes of driving or not at all. I have replaced O2 sensors, EGR sensor, Idle Air Control valve, cleaned the throttle body. There is no codes, except when it came to the sensor replacement and the local Lexus dealer mechanics are scratching their heads. They say they have never seen this before, but after reading this forum, it seems like it is a common problem. I am, (if it ever stops raining here) going to rip of the Air Bypass Valve on the left side of throttle body (don't know if this is right) and clean it. It had the 70K mile maintenance done but I am at a loss if anyone has any ideas. They don't think it is the computer. It does not matter if weather is rain or shine. In general, I suffer this condition after about 20 minutes of driving.

Shaka_rob

Well, it looks like everyone is stumped.

JSM1284

Intermittant problems are the worse to diagnose.

charley240

iTrader: (6)

check all vacuum hoses. maybe still try to do an obdII diagnostic, maybe your CEL are burnt so it doesnt show.
goodluck
Charley

92ES5sp

Weird. I actually had a similar problem at about the same mileage as your 98. Ir was more of an intermittent low idle. I said screw it. Pulled the plenum off and cleaned the EGR and IAC valves. and the upper runners too. Changed the v.c. gaskets while i was in there too. Vacuum lines were triple checked by me. Put it back together and no problems since.

Shaka_rob

Thanks, I probably missed something when I went in there to give it a cleaning. Will do it again.

joyndc

I had a rough idle on a 1994 Lexus ES300 V6. I cleaned what I thought was called the Idle Air Control Valve. My understanding from other posts is that it is a separate throttle plate located below the main large throttle. The main throttle plate feeds air during cruise and is controlled with a mechanical cable. The idle throttle plate is controlled by a solenoid. The throttle plate seems to get gummed up such that the solenoid cannot operate it.

I sprayed carb cleaner into the idle throttle plate area, let is soak, and blew it out with compressed air. The intake port to the idle throttle plate is just before the main throttle plate and there is an exit port just after the main throttle plate. Basically bypasses the main throttle plate during idle. The main throttle plate during idle is closed since it is mechanically linked to the gas pedal with a cable.

Note, there is a second port out of the idle throttle plate area that connects to the top of the engine. I disconnected this to prevent carb cleaner blowing into the engine body.

I apologize for this poor posting/explanation. This was all based on a very good post with pictures where the poster actually dismantled the throttle assembly to get to the idle throttle plate. From that and the hookup I surmised the above functioning. In any event, it fixed my problem.

Here's the link to the writeup:
http://us.lexusownersclub.com/forums...opic=30723&hl=

marcmindte

Same year car too. Mine starts to idle rough after about 20 minutes too, but really gets bad after I’m driving for about 2 hours. Mine begins ONLY when I’m at a cruising speed (usually above 40 miles per hour). Here is what happens: I’m driving down the freeway, and all of a sudden, the rpms go up to 4000 and then all the way down to almost zero. The car almost stalls out. Its like the car is getting too much gas, then not enough.
I changed the spark plus, a couple of sensors, and even cleaned with SeaFoam through the brake booster line, but its still doing it. Its been doing this for about 9 months now
Does anyone know how many sensors (fuel and others) are in this car? Maybe ill just start replacing one at a time.

Thanks

Shaka_rob

All, I appreciate the shared information. I am going to the site with pictures and rip the thing apart and clean it, paying close attention to sources of vacuum leaks and dirt in moving parts. Keep in mind that I can feel this when cruising speed, usually 45-65 mph, usually going up hill. I throw the car into 'neutral' and watch the rpm's bounce all over (300-900). This boggles the imagination. Shaka

Xterminate

i have the same problem like last week. I changed spark plugs, cleaned the iac and everything. Finally they figured out that my spark plug wires needed to be changed because it causes arching in electricity that is why the car shakes. After paying $138 bucks including the labor, the car no longer shakes.

I highly advise you to ask the dealer if they check through the spark plug wires or not, if they have and they say they are ok then I'm sorry I'm off no help. But otherwise, please do what I said as they miss those "small" checks a lot.