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Just took delivery of my new 240k miles SC430.
It hasn't been used for a year so MOT expired.
Lexus service history up until 235k miles.
I am now getting it ready for MOT; there used to be a CEL caused by P0171 and P0174 which I seem to have cured by cleaning the MAF, after which I tested it as per workshop manual. Both temp. and airflow measurement ok. Also reset the ECU
There's still a rough idle and I got below measurements.
Do I have 2 defective O2 sensors?
O2 FT B1 S1 19,71%
O2 FT B1 S2 99,15%
O2 FT B2 S1 15,59%
O2 FT B2 S2 99,15%
O2 S B1 S1 0,05V
O2 S B1 S2 0,8V
O2 B2 S1 0,1V
O2 B2 S2 0,09V
Fuel Sys #1 en #2 CL
Short FT 1 19,5%
Long FT 1 28,8%
Short FT 2 19,5%
Long FT 2 29,6%
The DTCs indicate Lean mixture
The voltage in B1 S1 is low assuming engine idle greater than, or equal to 1500RPM. B1 S2 has marginal voltage both should be at 1.0volts
What the experience in the thread pointed out, was cleaning the Mass Air Flow sensor did not resolve his problem, replacing it did. His was a perceived hesitation and rough idle.
Now you need to check the fuel trims at 2500 rpm's. This will tell us if it's a vacuum leak, or we need to look at other things. This is not a O2 issue.
oh, and make sure your pulling those numbers with the engine at temperature. Give us the short and long fuel trim percentages at the higher rpm.
You should also check all of the rubber vacuum lines. All are suspect on our cars due to age.
I found several that were cracked causing vacuum leaks.
dont ignore it...you may end up replacing good parts.
yeah bgw, I would bet he has one or more vacuum leaks. The op comes back with the fuel trim percentages at the higher rpm. we'll know for sure just from that. It's awesome the op came with all the information he did. It makes it really easy to narrow the problem down . If it is a vacuum leak, he'll be able to know if he fixed all of the vacuum leaks too. All he'll need to do is look at the fuel trim percentages again at both idle and the higher rpm. Fuel trim is a great diagnostic tool.
yeah bgw, I would bet he has one or more vacuum leaks. The op comes back with the fuel trim percentages at the higher rpm. we'll know for sure just from that. It's awesome the op came with all the information he did. It makes it really easy to narrow the problem down . If it is a vacuum leak, he'll be able to know if he fixed all of the vacuum leaks too. All he'll need to do is look at the fuel trim percentages again at both idle and the higher rpm. Fuel trim is a great diagnostic tool.
You know, I bet a stuck open PCV valve might cause a lean rough idle
You know, I bet a stuck open PCV valve might cause a lean rough idle
that's one of many possibilities for a vacuum leak. Other things even as simple as the oil fill cap not on good. The oil dipstick not seated. Intake tube between the maf and the throttle body. Throttle body gasket, intake gasket. Any vacuum line, any leak in the pcv system. If it had a plastic intake you would have to inspect it for crakcks. 240 thousand miles none of the above would surprise me. With a total fuel trim percentage of almost 50%, I'm surprised it even idles.
02-23-18, 07:00 AM
New owner; O2 sensor problem?
