Low idle 99 LS, but no CEL
05-19-17, 02:56 PM
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Low idle 99 LS, but no CEL
I have a 99 LS400, with 140k on the clock, lately it has been having a low idle and then back to normal idle. Engine runs fine, when low idle engine does not shake, very smooth, no CEL or anything. Only noticeable when in drive and at a stop. Throttle body has been cleaned and made no difference. All maintenance is up to date. I checked my ECU last year with everyone’s post about the caps going bad and mine looked fine. Does anyone know Whats wrong?
11-13-17, 01:29 PM
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I have a 99 LS400, with 140k on the clock, lately it has been having a low idle and then back to normal idle. Engine runs fine, when low idle engine does not shake, very smooth, no CEL or anything. Only noticeable when in drive and at a stop. Throttle body has been cleaned and made no difference. All maintenance is up to date. I checked my ECU last year with everyone’s post about the caps going bad and mine looked fine. Does anyone know Whats wrong?
Anybody got ideas?
11-13-17, 01:43 PM
#3
Lexus Champion
Coolant sensor original? Thermostat original? Spark plugs original? PCV valve, PCV valve grommet and PCV valve hoses(right and left bank) origina?l Condition of Negative grounds? Checked RPM with meter vs instrument cluster? Original.Oxygen sensors (pre-catalytic)?
11-13-17, 02:59 PM
#4
IF you have a low idle during first start/warm-up, you will want to look at the water temperature switch as noted by YODAONE.
The operating idle speed is maintained by a stepper motor in the ISC valve. It needs to be clean and not stuck.
The operating idle speed can be messed up by some intermittent problems in other actors, like the EGR valve, and, if you have an intermittent fast idle at operating temp, the power steering idle up valve. The air-conditioner circuit also kicks up the idle. Does your engine speed up when you engage the compressor?
Colin
The operating idle speed is maintained by a stepper motor in the ISC valve. It needs to be clean and not stuck.
The operating idle speed can be messed up by some intermittent problems in other actors, like the EGR valve, and, if you have an intermittent fast idle at operating temp, the power steering idle up valve. The air-conditioner circuit also kicks up the idle. Does your engine speed up when you engage the compressor?
Colin
11-13-17, 03:22 PM
#5
I had low idle, to almost stalling at times and it turned out to be my AFM. It would only occur when the car had warmed up tho.
Does this model have a power steering idle valve?
Does this model have a power steering idle valve?
Last edited by Moarpower; 11-13-17 at 03:58 PM.
11-13-17, 04:12 PM
#6
11-13-17, 09:16 PM
#7
Lexus Champion
Cannot use on 1990-1994 LS400's MAF sensor you will destroy a $900 part...
Not sure about 1995-1997 LS400's, but you can definitely use to clean 1998-2000 LS400 MAF sensors.
It make a slight difference.in idle quality...especially if you use K & N reusable oil.impregnated air filters....sometimes excess filter oil collects on MAF sensors.
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12-04-17, 02:53 PM
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IF you have a low idle during first start/warm-up, you will want to look at the water temperature switch as noted by YODAONE.
The operating idle speed is maintained by a stepper motor in the ISC valve. It needs to be clean and not stuck.
The operating idle speed can be messed up by some intermittent problems in other actors, like the EGR valve, and, if you have an intermittent fast idle at operating temp, the power steering idle up valve. The air-conditioner circuit also kicks up the idle. Does your engine speed up when you engage the compressor?
Colin
The operating idle speed is maintained by a stepper motor in the ISC valve. It needs to be clean and not stuck.
The operating idle speed can be messed up by some intermittent problems in other actors, like the EGR valve, and, if you have an intermittent fast idle at operating temp, the power steering idle up valve. The air-conditioner circuit also kicks up the idle. Does your engine speed up when you engage the compressor?
Colin
12-04-17, 02:54 PM
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Yes, it does and I replaced mine and with new hoses. Still did not do anything for the low idle.
12-05-17, 08:44 PM
#11
Lexus Champion
Meanwhile, inspect and test all grounds, battery terminals, battery cables, Alternator and battery.
Check out forum postings on those topics.
12-15-17, 10:09 AM
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12-15-17, 10:33 AM
#14
clean air-mix path
12-17-17, 05:24 PM
#15
Most likely the TPS (Throttle Position Sensor) is going out or being set to low. If you have a scanner then take a look at the TPS parameter. At idle, in park & AC off, it s/b set around 12.5% & the RPM s/b at around 650. You can play w/ the TPS by losing up the 2 screws then slightly turn it left or right. If yours is running fine & doesn't bog down when it's sitting at 400 RPM, I wouldn't mess w/ it unless you know what you're doing.