Juelz21

EthanS

I'm in the exact same boat, but in addition I have an on-again off-again P0420 check engine light ( drivers side catalytic converter malfunction) and poor mpg's (Most of the time <13mpg)
Not sure if the low idle, bad mileage, and cat efficiency issues are all tied together?

I have cleaned my throttle body extensively, cleaned the air mix path extensively. The air intake filter isn't spotless but is not in any way in poor condition.
Cannot find any exhaust leaks near the cats.
I have switched the downstream (post-cat) o2 sensors and the P0420 did not switch to P0430 (passenger side cat malfunction), so it is not the downstream o2 sensor going bad.
PCV valve and hoses have all been replaced within the last year.
Oil and spark plugs are always kept fresh, as they are currently.
I have not cleaned the MAF in any way. From what I hear, cleaning the MAF on a 98-00 vvti 1uz is risky - prone to cause more issues than leaving it alone.

I have sprayed carb cleaner all over intake tube and vacuum box/hoses with the engine idling - no sign of vacuum leaks with that test.
I have NOT sprayed carb cleaner anywhere under the car with it idling. I do want to inspect the idle-up power steering valve for vacuum leaks. I will try to do that this weekend and report back.

Cold start: idles about 1200-1500 rpm as expected, both with A/C on and off
Once warm with a/c off: very low idle 300rpm range ONLY IN DRIVE & REVERSE. In PARK & NEUTRAL decent healthy idle roughly 700-800 rpm
Once warm with a/c on: DRIVE & REVERSE acceptable but low 600rpm... PARK & NEUTRAL slightly high but perfectly acceptable 800-900 rpm range

I have heard multiple claims that this low idle issue can be cause by bad engine mounts...? That doesn't make any sense, but mine are old and could use replacement. I don't have much faith that engine mounts affect idle, but I suppose that's a possibility...

Open to any suggestions at this point, but only from those who have had a low idling vvti 1uz and have fixed the problem. Too many people on this forum (and all over the internet) suggesting fixes but they are just shooting in the dark (i.e. suggesting to clean/tweak the Idle Air Control Valve, of which the 98-00 vvti 1uz does not implement). Please don't contribute to the clutter.

RA40

iTrader: (6)

The engine coolant temp sensor threads would be my suggestion to read through.

Juelz21

EthanS

Glad you mentioned that. My ECT sensor is currently 11k miles / 25 months old. The issue has persisted throughout that time.
It is the Delphi brand ECT sensor.

Juelz21

dlcoffin

I'm having the same issue as well, with my 1997 ls400. low idle when warm, unless i have the ac on for the kick up. isn't there 2 sensors for temperature? One to the ecu, and the other to the dash gauge? The one connected to the dash gauge doesn't have anything to do with temp being sent to the ecu, is that right?

RA40

iTrader: (6)

The sensor for the coolant temp that is relayed to the ECU for fuel trim. Not the dash gauge. Many of us have replaced this at or beyond the 100K miles mark. At extended miles they tend to come out in two pieces or the connector wire shows severe corrosion.

Should be ok. When LScowboyls was here he preferred the Toyota sensor. Your situation has other factors involved since it has persisted even with the ECT replacement. I don't have familiarity with the VVTi version to suggest a direction. Keep us posted.

Yamae

Have you also cleaned two air mix passages using a compressor and enough solvent?
These 2 passages are one of weak points of aged 1UZ-FE VVT-i engines. I have fixed your type of problems a lot among 98 and after.

Juelz21

Juelz21

Juelz21

EthanS

Well, using an air compressor is not something I have done to the two air mix passages yet. All I did was take the cover off with the engine running, and sprayed about half a can of cleaner with the little straw attachment into the holes. The engine died a lot when I did this.
Maybe I should repeat this process with more solvent and compressed air next time?

Yamae

Without using an air compressor, it is not quite effective, I must say. Read the thread below and you'd know more about the method by MngreLMat.
https://www.clublexus.com/forums/ls-...ml#post8906720

Remember that you need to do it while the engine is idling+ to avoid the cleaner accumulated in the cylinder and causes the liquid hammer problem. Also the negative pressure is always needed there and this helps to clean passages more. You almost need 3 hands to do these simultaneously and you'd better ask someone to assist. I mean that one hand holds the cleaner can and the second hand holds the air compressor gun and third hand controls the idle speed not to halt the engine.

As MngreLMatt has written, "Use a couple of bottles if you have to", one can is often not sufficient. I also suggest you to try this twice while the engine is still warm may be waiting for half an hour or a bit more. If these are not successful, you probably need to remove injectors and clean them using a ultrasonic cleaner when the clogging is too bad. The most important passage is within the injector. It is so narrow that the passage is easily blocked. Once 1 injector is badly blocked, the air goes to other 3 injectors and it is not easy to clean the blocked injector. That's why you often need 2 cans and the compressed air.