Funky Idle & Hard Start Woes....

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

Nov 23, 2003
I posted up in another thread last month & no one replied so I thought I'd start a new one...

I've been having the some problems with the wife's 97 LX450.
The thing that has been bugging me the most is it seems completely random.
It will have issues during one running cycle, but then once you shut it off, it runs fine.
Here is a timeline with symptoms.

Over the last few months:
*When warm, idle would drop & rise (500-2500rpm). This would happen at a stop light or such.
It would be fine at the next light.

This is getting more & more often:
*Would do the same as above on start up. If we shut it off & restarted it, it would be fine.
*Other times it wouldn't start at all, but then the above would happen after a while of trying (I would smell fuel afterwards as well).

The not starting is getting more & more common, & is bugging the Wife (& me for fear of her getting stranded).

It has recently thrown a code ending in a 0116 a few times (coolant temp sensor).

Things I've fixed/Changed:
Fuel Filter
Dizzy Cap & Rotor
Cleaned/gapped blugs
Checked for vacuum leaks (starter fluid).
Siliconed/lubed 3 throttle cables at throttle body.
Checked intake hose for cracks
Checked/cleaned sensor connections on the dizzy & intake.
EGR filter (12 months ago).

What should I do next?
Last edited:
If it's throwing a code, you need to find out why. That's a fairly unusual code to boot.

P0116 only gives the sensor itself as a problem, or a problem in general with the cooling system.

I would check the main engine wiring harness found behind the engine (near the EGR pipe). Those have been known to be toasted by the EGR pipe, resulting in periodic shorts.
It hasn't thrown that code in almost 2 months.

It's been running ok for the last few weeks, but then started doing it again this week.

Twice leaving the wife stranded (at our house).
Worst part is that when I get home later that day/night, it fires right up.

I checked as much wiring as a could....(spent 30 minutes looking at everything).

A lot of the wires are in loom/plastic, so I couldn't see the wires themselves, but there was no melted/frayed loom/covering.
Also found it difficult to check the wires that run along the block under the exhaust manifold.
Just because the loom/plastic looks fine doesn't mean that the wires are definitely ok. The wiring insulation gets brittle with age, wires rub together while driving, and the insulation chips away. Then you get intermittent shorting across circuits where the insulation is missing. This can happen without damaging the loom. Open the loom and take a closer look. This is a very common problem with the 1fz.
I should have phrased that a little better.

I'm not talking about the type of loom you can open.

It's the sealed plastic covering.
The only way to "open" it would be with a blade, which would leave all the wiring expose.
It's getting worse...

Tonight, it as really hesitating/sputtering.
I grabbed a flashlight, & it wouldn't restart.

After several minutes of trying, it fired right up, but the idle was racing at 2k.
my 4runner threw the code for colant temp sensor, ran like you are describing, changed it out and ran normal again
Sounds like it's time to take it to someone who knows about these.
Gee... Thanks for the help there.
How old is your intake hose? I've seen a few recently that the owners swore were good, until we flexed it at the accordian fold and you could see minute cracks on the underside of the hose. In my experience, if it's older than 5 years it's suspect.
my 4runner threw the code for colant temp sensor, ran like you are describing, changed it out and ran normal again

x2. My bet is right here. Will definitely cause your symptoms, fuel/air ratio related...
I picked one up this morning...

Only problem is I've spent 45+ minutes trying to find it on my block.

Searches are no help.

Can anyone tell me the exact location?

Is it next to the 3 ECT sensors?
Behind the Alt?
It looks like (from the FSM) that it's right above the oil filter.


  • insp.pdf
    29.7 KB · Views: 232
Temp sensor is below the intake manifold.

It could also be a leak in the air intake downstream of the VAF meter. Check the air cleaner hose and the throttle body. The hose can crack and give big leaks. And the throttle body can come loose.

I also had similar symptoms with a bad O2 sensor, although not as extreme. The sensor was almost new and was not giving any error codes but the engine would barley run. After replacing the sensor the problem was solved. I don't understrand how the O2 sensor could cause this result but it did.
A pic is worth a 1000 words.

It took me less than 10 minutes to swap it out.

Yesterday, I found every one but that one.. I thought the wires to it were the one to it's left.
I couldn't see it because of the intake... I even tried my mini mirror.

I'm pretty sure the intake is fine (no cracks) for 2 reason.
I pulled & inspected it when I swapped the wires (to make it easier).
And I also tried the starter fluid trip on the motor looking for vacuum leaks.

I'll post up how it runs with the new Coolant Temp Sensor.

If the problem persists, I'll move on to the other sensors (02, etc. etc.).

Here is a pic of the exact one in case anyone else is looking for it....

Well, it's been almost 2 weeks & Lexus is running much better.

The startiing/idle issue has completely disappeared since swapping in the new temp sensor.

Users who are viewing this thread

Top Bottom