1UZ low idle, and start problem,SORTED!!!!.

["Z" UTE]

Hi guys, just thought I would document the problems I have experienced with a 1UZ-FE. Any one with a solution, please add your 2cents.

Problem No 1. Engine is very hard to start when dead cold. However starts great, when warm, or the ambient air temp is high.

I have pulled the Idle air control valve(IAC), cleaned greased and refitted, I actually adjusted it out of position, to see whether it worked, when re connected. Fired up, and the IAC did its thing, so all good on that front.

Bridged the fuel pump connectors at the diagnostic port, no change.

Removed and flow checked the cold start injector, all good, refitted still no change.

Clamped off fuel return line, and got a rise in RPM, but no change in start.

Could not get a fuel pressure test done, no one had appropriate fittings.

Local Soarer guru, suggested that as the car started fine when the fuel tank was hot, the non return valve in the fuel pump may not be working, replaced pump, and filter, no change.

New plugs and leads fitted, (grasping at straws here) no change.

The TPS has not been removed or played with, as the factory tamper paint is still covering the screws.

Problem No 2. Occasionally the idle RPM will drop to 200rpm at traffic lights etc. No biggie here, as the engine does not stall, even with A/C on, got to love Toyota's V8.
Cold start idle is only about 600rpm, a bit low in my opinion.

Combining the 2 problems, I am starting to think that, either the fuel pressure regulator, or pulse dampner on the fuel rail has a perforated diaphram.

What have I missed? Any pearls/gems of wisdom would be quite welcome at this stage, guys please help me out, cheers Chuck.

[2jzhilux]

if the pressure regulator diaphram is stuffed you should have fuel leaking out of the vaccum hose side

["Z" UTE]

if the pressure regulator diaphram is stuffed you should have fuel leaking out of the vaccum hose side

Not a whiff of fuel there, so that rules that one out. Thanks for the input.

Should have mentioned, running standard ECU, and no codes are forthcoming from the diagnostic port.


cheers Chuck.

[Aphox]

I imagine they're very similar but i had similar problems that was fixed by replacing the temp sensor for the ECU in my celsior.

Good luck. I've just had similar joys.

[CrUZida]

1) Try the temp sensor above.
2) Clean the TB and verify the TPS is in IDL
3) Replace the caps in the ecu.

["Z" UTE]

I think the air temp sensor would be part of the AFM, would that be accurate?
Water temp, the only seder I could find was the guage sender, single pin as per most Toyota's.

The throttle body was removed and cleaned, when I did the cold start injector.

Low idle problem, could be that the throttle cable was stretched big time.
The throttle arm was about 8mm away from the idle stop. Could that have been someone playing with the TPS? maybe they had a can of yellow paint.! I have heard of some guys (Yanks with Soarers) adjusting the TPS to achieve the desired idle rpm. BTW the TPS is in a prick of a position, to test the circuits.

To further explain the cold start problem, most 1UZ's fire up witin the first 3- 5 seconds of cranking. Crank mine for 3-5 seconds, stop wait for the circuit opening relay to shut off the fuel pump. Try again, engine will almost start, but will be rough as guts. I stop short of a start, and again wait for the circuit opening relay to shut off the fuel pump. Third sart attempt with a few mm of throttle, and she roars into life without a drama.

Will test start again tomorrow. Thanks for all the help, much appreciated, cheers Chuck.

[CrUZida]

Yeah, thats a serious problem you have there...

See if you can get your hands on a working ECU, help eliminate a heap of potentials.

[Mos]

I think the air temp sensor would be part of the AFM, would that be accurate?

Yep, part of AFM.

Water temp, the only seder I could find was the guage sender, single pin as per most Toyota's.

There will be an ECU temp sender also. It's there, keep looking

Mos.

["Z" UTE]

Mos, found the water temp sender,t he little bastard was hiding right under the drivers side coil! Checked it against another sender from a spare engine, the impedence was a bit higher, so swapped 'em over, will try a cold start again tomoz.

cheers Chuck.

[ReQuieM]

Yeah I was going to suggest the water temp sensor, mine acted like this when i accidently knocked mine off on the 1JZ. The one on the 1JZ is on the pipe on the engine side of the top thick return line.

Might be worth a check

["Z" UTE]

Guys SUCCESSSSSSSS at last. It was the water temp sensor, located under the coil. Fortunately I have a spare 1UZ, and was able to compare the resistance in both sensors. removed them both, and tested in cold water, and 100degc water, a significant difference. To all concerned particularly Aphox, Mos, and CrUZida thanks heaps.

The car starts first turn of the key. One very happy chappy,

cheers Chuck.

[CrUZida]

Wow, thats another person whose had very similar issues.

I'm beginning to wonder why the ecu didn't throw a code ?

[Mos]

Good to know you sorted it Chuck
No need to thank me, others suggested it

Peewee, there is no reason for the ECU to think there's anything wrong with the sensor if the value is still within an acceptable range - too bad if this throws the mappings out to the point where it's hard to start - that's just bad luck... Without a secondary sensor you can't check for this mode of failure.

Mos.

[CrUZida]

But surely if its that far out when its cold, then it would be even further out when its hot.

But I suppose its depends on how it fails.

[Mos]

Well... they go from around 10-20Kohms at -20 degrees to 100-250 ohms at 100 degrees...
If it's increased in resistance it will think it's colder (so I couldn't really explain why it's harder to start - unless it's flooding the engine), but if it's decreased by even a few K it could think it's at 80 degrees instead of 20, and as the resistance will never be negative, the error could drop to almost nothing at the higher temps...

Chuck - you did say it increased at low temps - what did it do at 100degs?

Mos.