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97 Lexus LS400 Always Running Rich at Cold Start. Is it normal?
My 97 Lexus LS400 has always been running rich (strong exhaust smell) at every cold start for about a minute & my overall MPG (20% city driving & 80% highway) is consistently at slightly less than 18 (EPA MPG specs for Lexus LS400: 17/23 city/highway & 19 combined). Car is well maintained & running fine. Perhaps I have a sluggish or bad ECT sensor? I haven't changed the ECT sensor for about 10 years so just wondering what's yours before I go ahead & replace it with a new one. Thanks.
My 98 smells like it runs rich in cold startup too. I had no idea what's going on. It was pretty substantial and I blindly asked my friend about it with no context, and they said yeah it was smellier than they would expect.
I changed the PCV valve a few months ago. It was pretty gummed up, probably still mostly working but maybe the valve was starting to get sticky. You might want to replace the hose running to the intake too, that can get crummy as well. https://www.clublexus.com/forums/ls-...l#post11598697
I'd say it's gotten at least 50% better since I changed it. It's still kinda rich, and it should be as cars run rich during cold start to heat up the cats faster, but nowhere near what it was. It smells like a normal car now, instead of that "old car" smell. You know what I mean.
Thanks for letting me know. I recently replaced the valve cover's gaskets so I also replaced the pcv valve, grommet & hose. This morning, I went ahead & ordered a new genuine OEM ECT sensor after I posted the question through Amayama.com for only about $20 + $10 for shipping. This website sells genuine OEM parts w/ good price but it takes a few weeks due to international shipping, mainly from Japan & the UAE. I've purchased parts from them for years.
Fyi, I also have a 2000 LS400 w/ only 50k miles & in brand new condition inside out. It's hard to believe the interior still has the new car smell even after all these years. I gave it to my son a few years ago. I've asked him the same question this morning & am waiting for his answer. Here's a few pics of it.
I also did this (for a 2nd time) during the same maintenance I think. I think it's unlikely to have affected anything, but, it's the only other thing I did to my car during that time period. It's been fixed since then. My around-town fuel economy went up, fumes went away, etc.
I'm aware of Yamae & your "air mix path" clogging post & did the cleaning on the 2000 LS400 a couple years ago anyway even though I didn't experience the issue. Perhaps it's due to it being low mileage. Thanks anyway for providing the link. It was very nice of Yamae & you for taking the time to write it up & translate, respectively & turned it into a very worthy thread for our forum.
Btw, this "air mix path" cleaning procedure only applicable to 98-00, correct?
Yeah, 1997 and earlier used a different type of injector. In 1998 they switched to air-assisted fuel injectors, and those little holes bypass the throttle plate and feed that system.
Running rich after a cold start is normal. The O2 sensors need time to warm up from exhaust gases. In this time, the ECU is running off of a "basemap" (open loop) which is "guessing" what the O2 readings and calculating the air/fuel mixture based on that. This "basemap" is generally tuned to run a bit rich to keep combustion temperatures down, among other things. When the O2 sensors are warmed up enough, the ECU switches to closed loop and starts running off of their readings.
Also, in my experience; all Toyotas from this era are smelly during cold starts, I think it's due to the cats they used. My 1MZ Avalon was the same way.
For what it's worth, I park my car back-first in a 1 car garage. I get a pretty good whiff of what the car smells like if I walk back into the house after starting the car. I don't smell rich exhaust on cold start anymore in my car, it's just normal exhaust.
Running rich after a cold start is normal. The O2 sensors need time to warm up from exhaust gases. In this time, the ECU is running off of a "basemap" (open loop) which is "guessing" what the O2 readings and calculating the air/fuel mixture based on that. This "basemap" is generally tuned to run a bit rich to keep combustion temperatures down, among other things. When the O2 sensors are warmed up enough, the ECU switches to closed loop and starts running off of their readings.
Also, in my experience; all Toyotas from this era are smelly during cold starts, I think it's due to the cats they used. My 1MZ Avalon was the same way.
Yeah, I'm sure all cars run rich at cold start when the ECU is in the Open Loop & some do run a bit more richer than others due to different car manufacturer's design settings. You're right about O2 sensors need time to warm up from exhaust gases but those are mainly the older style 1-wire & 2-wire sensors. The newer 3-wire, 4-wire & 5-wire sensors (LS400 uses 4-wire) have heater elements built-in & heat up by the 12V. I hooked up the scanner prior to a cold start & noticed the LS400's ECU switched from an Open Loop to Close Up in about 30 seconds.
07-07-24, 07:09 AM
97 Lexus LS400 Always Running Rich at Cold Start. Is it normal?
