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ST185 Idle Problem.


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#1 Stag76

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Posted 11 May 2014 - 08:21 PM

I've been chasing an idle problem for a while. When it's cold. it idles roughly, and when it's hot it dies.

 

The engine is stock standard, and has done 150,000 k's. It is a one owner car I bought the a few

months back, and the problem came with it.

 

I've looked for vacuum leaks, and replaced and zip-tied all the vacuum hoses. Then I've done the

following.

  

  Compression test (All Good).

  Injectors cleaned and reconditioned.

  Injector insulators replaced.

  Idle Valve Replaced.

  Rubber couplings between TB and InterCooler and Turbo and InterCooler replaced.

  Plugs, Plug Leads, Distributor Cap and Rotor Replaced.

  Air Filter replaced.

  Fuel Filter Replaced

  Fuel Pressure Checked.

  Different AFM tried.

  Diagnostic Codes Checked - NO Codes

  CLT Temp Sensor Checked  - OK.

 

When the A/C is on, it idles better (doesn't die due to the idle-up), so I added an extra idle

adjustment by teeing an adjustable valve (sourced from a Camry) into the air line that

supplies the A/C Idle up.

 

This has fixed the idle in so much as it now idles reliably at whatever revs you set it at, hot or cold.

I've also tried adjusting the idle air bypass screw on the AFM, and this also stops it dying, but

the idle is not as steady as using the extra idle air valve, probably due to this adding air before the

TB, and the air valve after the TB.

 

The fact that introducing additional air has fixed it suggests that it is not a vacuum leak,

as what I've done is to effectively introduce air after the AFM, or the same as a vacuum leak.

 

Apart from this, it runs well throughout the rev range, doesn't overheat, run rich or any

other displays of bad manners.

 

Any suggestions gratefully received.


Edited by Stag76, 12 May 2014 - 02:06 PM.


#2 Cuts

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Posted 11 May 2014 - 08:47 PM

coolant temp sensor possibly.


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#3 silycr

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Posted 11 May 2014 - 08:50 PM

I think i should put this as my sig

 

Have you tried codes?



#4 Stag76

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Posted 12 May 2014 - 02:05 PM

I checked the diagnostic codes - just a continuous .25 Second flash, NO Codes.

 

I checked the resistance of the CLT Sensor - 1.185K Ohms at engine temp of approx 30 Degrees C, so within spec.

 

Thanks for the input.


Edited by Stag76, 12 May 2014 - 02:07 PM.


#5 silycr

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Posted 12 May 2014 - 03:24 PM

I'm lost. Looks like you've tested or replaced everything I would have looked at. The only alternative is the ecu. Hopefully someone else has some more productive input....



#6 Stag76

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Posted 12 May 2014 - 05:17 PM

Maybe the Idle Control Circuit of the ECU is flaky. The fact that I have to add

air to make it run points to something not working as opposed to an air leak. 

If I unplug the Idle Control Valve when its running, it immediately idles at about

1500 rpm,..rock steady. Plug it in again and it dies.



#7 pinkst162formylady

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Posted 12 May 2014 - 06:03 PM

im pretty sure adjusting the screw on the afm is a big no no.

theres also an idle adjustment screw on the throttle body.

other possible thing is the tps is out of calibration. if its not set correctly the iscv wont kick in.

#8 Stag76

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Posted 12 May 2014 - 07:58 PM

I only messed with the AFM Idle screw to see if it would help. It is factory set. There is a post

on the MR2 forums that describes turning it 2-3 full turns counter-clockwise (ie reducing airflow)

from the factory setting to overcome cold engine hesitation.

 

TPS is in spec and calibrated.

 

I don't know what the Idle screw on the throttle body is for, as the idle is a closed loop controlled

by the ISCV.

 

Everything points to not getting enough air, and the only thing left is the idle control circuit in the ECU.

 

It's OK as it is with the additional idle air valve, but I would like to get it right.



#9 sainz 47

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Posted 14 May 2014 - 07:46 AM

throttle body may need cleaning they can get clogged up .




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#10 road and track

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Posted 14 May 2014 - 09:17 AM

the idle is controlled by a combination if changing ignition timing and alternation to the idle speed control valve. 

 

a missing engine thermostat can cause similar problems

 

this flap type AFM rarely needs any changes so long as people have not fiddled with it. we are just fixing one where the idle "switch" in it had been damaged by owners fiddling 


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#11 Stag76

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Posted 14 May 2014 - 05:43 PM

The Throttle body has been off and cleaned...the EGR Port was clogged with tar.

 

It warms up quickly, which suggests that the thermostat is in place and operating OK.

I've checked the coolant temp sensor resistance, and it is within spec cold, warm

and running temperature.

 

It appears to not be getting enough air through the idle valve (which has been replaced),

as it idles at 1500rpm with the valve disconnected, and the additional air valve I added

allows it to idle properly.

 

It's looking more like the ECU, however unlikely.

 

Thanks for the input.



#12 silycr

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Posted 14 May 2014 - 07:06 PM

Which car do you have? If you can get the part number on the ECU, I have a spare one here you could try if you're around the Brisbane area.



#13 sainz 47

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Posted 14 May 2014 - 08:43 PM

the black  sensoron the throtle body  has adjustment on it  and the throttle body has a adjustment screw for idle aswell




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#14 Stag76

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Posted 15 May 2014 - 06:24 AM

It's a 1989 ST185. Where is the ECU?



#15 silycr

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Posted 15 May 2014 - 06:48 AM

he ecu is behind the radio. If you pull the carpet back on the passengers side, you can see it



#16 Stag76

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Posted 30 August 2014 - 07:14 AM

I've finally got this sorted.

 

There was a split in the vacuum hose where it connected to the TVIS Actuator that was leaking enough vacuum to prevent

the actuator from holding the butterflies properly closed.

 

One of the plastic fittings on the Power Steering Idle-up pressure switch was also broken, so I blanked off both hoses.

 

Now it starts perfectly hot or cold, and idles smoothly at 850rpm.






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