Strange hesitation on 1SZ-FE

[Astronaut]

 
Hello! I bought Yaris 1.0L 1SZ-FE (2004, with 165000 km) and have no fault codes on it

 have some hesitation after fast/sharply pressing the gas pedal (hesitation from idle to 1500-2000 rpm, like if the engine is choking),

but if I press gas smoothly - the engine normally gains speed and power.... also no lack of power from 2000 to 7000 rpm.

what I did:
-new spark plugs (Denco)
-new air filter 
-new motor oil 5w30
-checked MAF and IAT sensor (clean like new)
-cleaned throttle body (was not so dirty)
-cleaned IACV (was clean almost)
-cleaned PCV
-tested TPS
-checked vapor solenoid
-tested camshaft position sensor  
-checked ignition coils (with multimeter)  

p.s. Few days ago I was able to get some data using the ELM327.. everything is fine there too.

The only thing that worries me - is the IAT sensor data. When engige is cold - sensor shows almost real temp.+17C(with real +16C outside), after few kilometers ride: +40...+60C (with still real +16C outside), but when I touch the intake box, where the  IAT is located - it is really warm... is it ok with this data? (when i took it out and measured it - tester shows 2.0 kohms)

I will appreciate any comments on my topic, thanks

[flash22]

check the resistance of the OCV (top left of the timing chain cover)

[Astronaut]

On 9/16/2024 at 5:57 PM, flash22 said:

check the resistance of the OCV (top left of the timing chain cover)

[flash22]

That's in the range, Fuel trims look right so it's not fuel or a vacuum leak

2k ohm is well out of spec for the IAT assuming you have the correct pins - do not buy cheap Chinese junk

[Astronaut]

19 minutes ago, flash22 said:

do not buy cheap Chinese junk

I think it is original from the factory... At least it looks like...

 

Quote

2k ohm is well out of spec

it is not for the 1SZ-FE?

it is not my photo, but I have the same:

 

[flash22]

what were the engine and ait temperatures when that reading was taken?

 

 

[Astronaut]

8 hours ago, flash22 said:

what were the engine and ait temperatures when that reading was taken?

 

After you asked me to measure the resistance of the VVT-I valve, I forgot to put the wire back on.🤭
And drove to work with the valve turned off...
Then I remembered and on the way back - I plugged it back in.
The most interesting thing is - that I did not get a "check engine" and also did not notice a difference in the operation of the engine with the oil valve disconnected or connected... Or it's my glitches.

[Astronaut]

11 hours ago, Astronaut said:

  VVT-I valve, I forgot to...

Today I removed the OCV solenoid and applied 12V to it - it clicks and opens (it's also perfectly clean, with only engine oil on it).

I also tried pressing the gas pedal sharply while the engine was cold (of course, it’s not advisable to do so, but I did it for testing purposes only) – there are no chokes or hesitation, and the car accelerates quickly.

However, once the engine warmed up and the temperature-light turned off - the chokes and hesitation began again when pressing the gas sharply... it is most noticeable in the 1st and 2nd gears of course

The biggest question is - why I didn't get the "check engine" light and zero OBD2 error-codes while disabling some sensors/solenoids,
maybe the ECU itself is defective...

[flash22]

can you check ocv resistance when the engine is hot, the issue goes away with the OCV disconnected ?

 

Some scan tools and apps can not read some systems

try a flash test by linking 2 pins of the OBD2 port, turn on the ignition and count the flashes on the dash

 

 

 

[Astronaut]

2 hours ago, flash22 said:

can you check ocv resistance when the engine is hot, the issue goes away with the OCV disconnected ?

 

Some scan tools and apps can not read some systems

try a flash test by linking 2 pins of the OBD2 port, turn on the ignition and count the flashes on the dash

 

 

 

On 88C coolant I got 8,8 omh.

Also I disconnected cable again and got P1346 on obd2 for the first time 

[flash22]

that sounds about right for the temp

 

[Astronaut]

4 hours ago, flash22 said:

that sounds about right for the temp

 

Do you mean, the IAT should to show +25C if I have +25C outside? Not +40C or +50C like in my case?...

[Astronaut]

Today I measured voltage (under ignition ON) in the OCV socket - it was 6.5 volts... (here is only 1V..) also yesterday I pulled the terminal off the solenoid again - and got no errors in OBD2 or "Check engine" light again..  after driving 12 km, even at 6000 rpm...so it works randomly.

as for me it is everything points to the fact that the problems are with the ECU..

 

[Astronaut]

Today bought fuel on different gas-station and cheked O2 sensors (Lambda), the 1st has range 0.1-0.8V, the 2nd - stable voltage. So, everithing are ok also...

So, what I did in 3-4 mounth:

-new spark plugs (Denco)
-new air filter 
-new motor oil 5w30 + new oil finter

-cleaned IACV (was clean)
-cleaned PCV (was not so dirty)
-cleaned vapor solenoid (was clean)
-cleaned throttle body (was not so dirty)

-checked TPS
-checked MAF and IAT sensors (clean like new, shows normal data in OBD2, IAT shows a bit higher than outside temp., but it is ok)
-checked camshaft position sensor  
-checked ignition coils (with multimeter only)  
-checked engine temperature sensor
-checked OCV (VVT-I solenoid in perfekt condition)
-checked O2 Lambdla sensors

-changed fuel station +added some "98" fuel (before was 95 only)

Hesitation after fast/sharply pressing the gas pedal still persists, extremely uncomfortable ride in the city...

P.S. If I will buy ECU - it is possible to reprogram it for the old immobilizer (in home-parking-garage working conditions)?

[flash22]

It's not the ecu, the OCV is PWM controlled, have you checked the OCV filter

[Astronaut]

2 hours ago, flash22 said:

have you checked the OCV filter

did not find it inside,

but I will check again with camera

[flash22]

its behind a nut/plug on the back of the head near the OCV (just under the intake manifold, you will need long nose pliers to pull the filter out

 

[Astronaut]

On 9/25/2024 at 2:21 PM, flash22 said:

its behind a nut/plug on the back of the head near the OCV (just under the intake manifold, you will need long nose pliers to pull the filter out

 Found, thanx. But also clean, almost like a new one..(

[flash22]

It has got a bit of a dark spot where the oil gallery is, I take it you cleaned it before putting it back

[Mushu84]

 

It can also be ignition coil failure that why is doing it when hot, check for cracks, check if you have any different value when hot 

 

also I had the same issue on an older car (vauxhall Corsa) where the MAF was acting up due to the fact it was not original Bosch and it didn't like that, after it was changed with original no issues.

[Astronaut]

2 hours ago, flash22 said:

, I take it you cleaned it before putting it back

Ok. will do it tomorrow)

2 hours ago, Mushu84 said:

 

It can also be ignition coil failure that why is doing it when hot, check for cracks, check if you have any different value when hot 

ig.coils looks like new and ignition spark plugs has the same colour(normal) + zero errors about fire missing via OBD2..

2 hours ago, Mushu84 said:

where the MAF was acting up due to the fact it was not original

I have original MAF and data from it looks like OK (1g/s or something like that on the idle and up to 25-30g on full gaspedal)...

today noticed only the TPS shows 0% on idle and only 67% on FULL press, not 100%... 0_o.. Is it OK? or need some calibration?

[flash22]

that did cross my mind that you may have worn tps with a dead spot, what about re-lubing the throttle cable after 20 years of active use it maybe a tad dry

[Astronaut]

9 minutes ago, flash22 said:

d that you may have worn tps with a dead spot

if I follow the % (during the OBD2 tests) while pressing the pedal smoothly and slowly - the % grows without interruption (1-2-3-4% and so on, up to 67%). the gas cable slides smoothly and does not "bite" anywhere

[flash22]

The TPS never reads 100% (only under testing)

 

[Astronaut]

Cleaned OCV filter - zero changes.

Bought used ECU.

Plugged it in, connected pins 4 and 13 on the OBD, turned the ignition ON for 30 minutes, turned ioff. The starter spins, but the engine does not start.