Engine hunting

[twinturbo]

Depends..

The symptops point to an Idle control issue..


Either that means the Idle control valve ( ISCV ) is not operating correctly, or the ecu is unable to control it correctly.

TT

[twinturbo]

My Turbo 2.9 idles beautifully for the first 30 seconds.. then starts hunting, then revs and drops right back.. I suspect the ECT may be an issue.. But on this car anything could be wrong..

What you realy need to do is get it full of water and then run it for half an hour, go through the rev range a few times to try and get some DATA into the ECU.

the full drive cycle for the ecu can't be replicated on a driveway as you will not get the full load data, but the ecu will be happier if it's had a bit more to learna bout.

TT

[deezee]

I didn't think any sierra came with a learning ECU. The ECU just adjusts itself within expected parameters and sensor input. Takes from cold to warm of an engine according to Toyota.

[twinturbo]

There's a few paramaters it stores.

Have you tried disconecting the battey? There may also be a fault code stored, and the ECU may even be in LOS ( one indication of this is the pump running constantly at ignition on. )

Check also on the FSOC forum, I think someone had simillar issues on a Twink in the last 6 months.

TT

[Enoch]

I have tried disconnecting the battery, i left the negative disconnected all last night. I have not yet checked to see if I have continuity on the valve - I am assuming it's just like a solonoid of some sort and takes a dc feed? I will bring home an oscilloscope later and see if I can find out a bit more. My simple mind tells me it's the valve but I suppose it could be an ecu fault. It's bloody strange that it happenned after my backfire though, I can't believe it was coincidence. The pump is doing what it should - ie running for 3 seconds at turn on, then just as it needs to with the engine running.
Thanks again for your help guys.
Dave.

[twinturbo]

I doubt it's an ECU fault, but if the valve is not faulty then and incorrect reading from one of the sensors or an air leak.

You could also try disconnecting the MAP sensor multiplug, in fact if you unplug all the sensors the ECU should drop to LOS.

Disconect, MAP, ECT, IAT, TPS, Rail Temp. Not sure it will even run but it's worth a punt..

This is a non lambda engine isnt it?

Ohh.. And have you touched the timing at all on the cams?

Applying 12V across the ISCV should throw it across ( +12v next to the notch in the plug.

TT

[twinturbo]

Also...

With the ISCV disconnected what is the base idle?

TT

[Enoch]

Hi TT, itis a non lambda, the base idle is just under 2k with the iscv connected - same with it disconnected. I have not touched the timing, the car seems to rev ok when the throttle is opened. I am at the office this morning but will take a DVM and scope home so I can see if teh ecu is trying to drive it. I am suspecting that the valve is stuck.
Will let you know....
Best and all that.