Idle Adjustment Problem?

[simmodrz]

G'day,

So I tried adjusting the idle yesterday as per the instructions from VFAQ... grounded the timing plug on the firewall and also the correct pin in the plug by the fusebox once the motor was fully warmed up and all electrics turned off etc.

I then adjusted the BISS screw to as close to 750 as possible which worked fine and then took off alligator clips and the idle just went straight back up to 1000rpm again (even after a 5 minute run).

Pre-Adjustment Idle = 1000rpm
After-Adjustment Idle = 1000rpm

Now the ECU has a modded chip in it... does/can whoever modded the chip, change the idle parameters so the computer itself is trying to chase 1000rpm at all times? (I'm not too clued up on ECU operation)

I mean I understand what the BISS screw is doing with all plugs earthed but then what/why is the ISC going back up to 1000rpm... is the ECU telling it to do so?

Cheers,
Simmo

 

[4piknup]

The biss screw only sets the position of the isc stepper motor so that it has enough range of travel for all engine requirements.
You cannot set this without being able to see the isc position. I have dsm link so that works for me. I don't know if a obd1 or 2 reader will show you isc position.

Is throttle shut?
If you put sticky tape over just the left port inside the throttlebody (on aircleaner side of throttle plate), what does it do?
Repeat test for the right side port.
Repeat test with both ports blocked.

What vacuum do you have at idle?

 

[blackvr]

Simon, firstly check the continiuty of the four coils inside the ISC motor ( approx 30 ohms).

Yes, using the data page of the ECMLink program ( Simons ECU has ECMLink), you can check the step count of the ISC ( around 10 -20 counts??) Yes, the ECMLink can set a target idle speed ( yours should be about 850 rpm.)

Lastly, the FIAV function in the throttle body is notorius for creating hi idle issues... All outlined in VFAQ.com

Any Perth guys able to come to the rescue for Simon ?

Mike

 

[simmodrz]

Hi Mike,

No, I haven't fitted the ECMLink yet... still just running the motor in with the "chipped" standard ECU and 450 injectors. So I was wondering if on these fixed "mod chip" ECU's can they have a pre-set target idle?

I'll do some reading on the FIAV...

Cheers
Simon

 

[simmodrz]

After doing a bit more thinking and reaserch I dont think it can be the FIAV... as with the engine warm, plugs grounded, BISS adjusted you can get a great idle (even if the FIAV is leaking I can still adjust to get a great idle).

As it is when the earth alligator clips are taken off that the ECU steps back in to control the ISC... thats when it jumps up from ~750rpm to ~1000rpm... so yeah... more pointing to ISC or ECU

 

[blackvr]

A half decent scan tool will be able to pull data from your "mod"chipped ECU... from that you should be able to see the ISC step count as well.

 

[4piknup]

After doing a bit more thinking and reaserch I dont think it can be the FIAV... as with the engine warm, plugs grounded, BISS adjusted you can get a great idle (even if the FIAV is leaking I can still adjust to get a great idle).

As it is when the earth alligator clips are taken off that the ECU steps back in to control the ISC... thats when it jumps up from ~750rpm to ~1000rpm... so yeah... more pointing to ISC or ECU

mine was the same, the faiv was only partly open and wouldnt shut all the way. the revs it added was too much for the isc to control.
blocking both ports in the throttle body, it should not idle at all. (it will eliminate vacuum leaks as a problem)
blocking the faiv when car is warm should have no effect. if it does idle lower, it tells the problem.
blocking the isc port will stop the engine hunting if it has that problem. if it has no problem it will not idle.

do the tests dude, and go from there. all you need is a bit of masking tape and pull the rubber elbow off the tb. 20 min tops.

 

[4piknup]

in the stickys in the evo1-3 section about isc issues, is a couple of youtube links to my ute. check them out and compare to what yours does.

 

[simmodrz]

Cheers I'll have a crack over the weekend, just got a multimeter yesterday too so I can check ISC and TPS settings etc too...

Thanks