Just bought a 1998 ls400 Previous owner was using regular unleaded fuel for awhile
12-12-13, 01:57 PM
#17
Driver School Candidate
Thread Starter
Wow so many replies thanks for all the input! It was my uncles car 1 owner, complete and regular maintenance car has a lot of miles though 250,000 so there in could lie the problem, Im a college student and just need the car to last 5 more months but would hope for it to last a few years.. so to solve the fuel issue i switched it to premium and im getting better gas mileage/ power! but the idle is getting worse when stopped at lights idles at 500rpm and every couple of lights rps go down to 350, almost sounds like engine knocking sometimes, ill take it to my mechanic have him clean the throttle body pull the codes, VSC off light is on with check engine light.. my uncle dove in it last night and said it never had that problem..
Thank you for all your input
J
Thank you for all your input
J
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BNastee (12-15-22)
12-12-13, 02:25 PM
#18
Wow so many replies thanks for all the input! It was my uncles car 1 owner, complete and regular maintenance car has a lot of miles though 250,000 so there in could lie the problem, Im a college student and just need the car to last 5 more months but would hope for it to last a few years.. so to solve the fuel issue i switched it to premium and im getting better gas mileage/ power! but the idle is getting worse when stopped at lights idles at 500rpm and every couple of lights rps go down to 350, almost sounds like engine knocking sometimes, ill take it to my mechanic have him clean the throttle body pull the codes, VSC off light is on with check engine light.. my uncle dove in it last night and said it never had that problem..
Thank you for all your input
J
Thank you for all your input
J
12-13-13, 05:15 PM
#20
Driver School Candidate
Thread Starter
Update! so the engine knocking went away, im switched to 91 fuel now, i think it possibly fixed itself.. the idle is still a bit rough so im going to clean the throttle body and maf sensor! thank for all your help!
12-13-13, 05:48 PM
#21
Lexus Champion
just a reminder to folks with a pre-95 LS400, do not clean MAF with solvent, you will ruin it (I see that jared's is a '98 so you are OK)
Last edited by LScowboyLS; 12-13-13 at 06:11 PM.
12-13-13, 07:38 PM
#22
Moderator
The air mix path can be accessed opening the lid which is located at the position of a red arrow indicated at the top left photo. It has two Philips screws but they can't be seen in this photo disturbed by the dark green harness. Remove the carbon and spray the cleaning solvent to those two black holes at the left and the right side. These two holes are connected to injectors to send the air to do the pre-mixing with the gas. Cleaning these two lines provides the better gas mileage and the better engine running especially at lower rpm.
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BNastee (12-15-22)
12-14-13, 11:06 AM
#25
Lexus Champion
Techron is available at Wal-Mart for a cheap price, I wouldn't pick my gasoline price or brand based on Techron, besides, other big oil companies have equally effective similar fuel system cleaners, such as Shell
12-14-13, 05:31 PM
#26
Oddly enough, I filled up at Mobil today, since I was a little lower than 1/8 of a tank. While you can buy the "Techron" separately, it's easier (and in some cases, cheaper) to just fill up at Chevron. Not really downvoting any other oil companies' fuel cleaners, but we use Chevron (with Techron) so I figured I'd just put that out there.
12-14-13, 05:37 PM
#27
Lexus Champion
Shell used to be the best gas and Chevron some of the worst of the big brands, but these days, who knows, they are probably much closer or essentially the same, gas has almost become a generic product - I would probably buy based on company environmental record if I bought full price gas, and in that case the company would be Sunoco
12-19-13, 08:04 AM
#29
Driver School Candidate
Speaking of fuel grades
Around here the gas stations have really been pushing up the differential between grades of fuel. They usually start by replacing their sign that advertises the price of all three grades, with one that advertises the price of regular only. When you see a station that only advertises a regular price, you know premium is super expensive there 
The typical spread between 87 and 93 octane around here has gone from 20 cents a few years ago to 30 cents last year and is now 40-50 cents. Note that this is independent of the price of regular, is it's not them maintaining a consistent percentage.... it's squeezing premium drivers while advertising lower regular prices, as more cars claim to needt premium.
So after 12 years of loyally running 93 octane in my LS400 I'm seriously considering dropping back to 87 octane. Looks from here that people have mixed results. Would like to hear more feedback on this from others who have done it.
The typical spread between 87 and 93 octane around here has gone from 20 cents a few years ago to 30 cents last year and is now 40-50 cents. Note that this is independent of the price of regular, is it's not them maintaining a consistent percentage.... it's squeezing premium drivers while advertising lower regular prices, as more cars claim to needt premium.
So after 12 years of loyally running 93 octane in my LS400 I'm seriously considering dropping back to 87 octane. Looks from here that people have mixed results. Would like to hear more feedback on this from others who have done it.
12-19-13, 08:51 AM
#30
My previously one owner car I believe never had premium used until I took over maintenance. I will say that after my second full tank of premium with a 20 oz bottle of Techron that my CEL threw a 430 code (driver side cats or O2) but after clearing and watching it, in the 2 months since (on my third full tank with Techron) it has never returned.
Related? no idea, but I will keep using Techron and Premium at every fill. I don't drive it daily so I don't mind the cost.
Related? no idea, but I will keep using Techron and Premium at every fill. I don't drive it daily so I don't mind the cost.