holden v8 5.0 hunting at idle

[351ciofgrunt]

Hey guys,

I've got a efi holden 5.0 V8 in a GQ patrol, recently it stopped dead and wouldn't start (it had no spark or injector pulse) so I replaced the ignition module with a rebuilt one and it's going again.

Except since getting it going I now have a new problem, it hunts at idle, the idle drops to almost stalling then picks up and drops again (also it would sometimes not restart after a hot shutdown until the engine had cooled down) I suspected the coolant temp sensor and have just finished replacing it however no difference.

Any ideas?

[RAY185]

Apart from checking for vacuum leaks, check battery voltage. Most Holden computers struggle with anything less than optimum voltage. If your battery is sus, try a good one.

[Struth]

Check the Idle Actuator Control, this can cause your issue as can the TPS.

Best bet is to get a mobile EFI dude out or go and see one to get the engine systems scanned. might cost $80 but will save a lot of rooting around.

Cheers

[tub350]

As above, clean IAC and throttle body, reset base idle.

[351ciofgrunt]

I got a mobile efi guy out to have a look but he said who ever did the conversion (not me) took shortcuts and didnt leave the diagnostic plug for him to plug into so he couldn't help me.

So I've done the following:

Checked battery, all good
Pulled throttle body, degreased, cleaned and ran compressed air through all galleries, ports.
Unscrewed Idle Air Control and cleaned.
Replaced fuel filter.

Still hunting at idle.

The next thing i'm thinking of doing is getting a new Idle Air Control but does anyone know how to test if the current one is not working? could I just unplug it and see if it makes any difference? if no difference then thats the problem?

[Struth]

How bad is the hunting, mine idled like a pig and hunted by 2 to 3 degrees, all caused by uneven cylinder compressions.

Hope that's not is but I checked everything else 5 times at least before pulling the motor down for rings.

Also it should not be difficult to hook up a diagnostic plug, I can let you know pin numbers on the computer to use if needed.

Does it have a MAF sensor, if so disconnect it, the engine should run even worse that way, if it doesn't then suspect the MAF sensor.

Cheers

[PGS 4WD]

I got a mobile efi guy out to have a look but he said who ever did the conversion (not me) took shortcuts and didnt leave the diagnostic plug for him to plug into so he couldn't help me.

So I've done the following:

Checked battery, all good
Pulled throttle body, degreased, cleaned and ran compressed air through all galleries, ports.
Unscrewed Idle Air Control and cleaned.
Replaced fuel filter.

Still hunting at idle.

The next thing i'm thinking of doing is getting a new Idle Air Control but does anyone know how to test if the current one is not working? could I just unplug it and see if it makes any difference? if no difference then thats the problem?

I see that all lthe time when I have to tune them, I can set up a set of jumper wires to get data and codes, you really need to ideally to see what the cause is. Resetting and cleaning the throttle is all good, do you know the proceedure to reset the IAC? It could be hunting due to mixture, MAP sensor, O2 sensor or ECU/program. It could be due to timing hunting or IAC control, the live data helps get an insight into what.

Joel

[351ciofgrunt]

What is the procedure for resetting the IAC?

Yeah I think I'm going to have to take it to a workshop.

[PGS 4WD]

Get the engine to operating temperature, create a vacuum leak, sizeable, like remove the booster hose, the engine will rev and gradually slow till the IAC winds fully in, disconnect the IAC plug (4 pin) and reconnect the hose, the vehicle may stall. Restart if necessary and adjust the idle stop screw to maintain a slow 450-500 rpm idle, reconnect the IAC. Ideally I use my scan tool to acheive the same number of IAC steps that the tune has in it for hot idle no load as this means the ecu is doing the least amount of adaption.

Cheers

Joel

[Struth]

Another method is to disconnect the computer, re connect, start engine and hold 2500 rpm for 10 seconds, shut engine down.. IAC should then be seated correctly.

Cheers

[351ciofgrunt]

Thanks for the help guys, I ended up finding the diagnostic plug (it was lying loose stuffed behind the centre console) so I got the mobile mechanic back who ran a scan for me and came up with no
errors. He then reset the IAC played around with a couple other things and it's all sorted now. Allthough stuffed if I know what caused it, but probably just needed to be reset after I cleaned the TB and IAC.

[lay80n]

Thanks for the help guys, I ended up finding the diagnostic plug (it was lying loose stuffed behind the centre console) so I got the mobile mechanic back who ran a scan for me and came up with no
errors. He then reset the IAC played around with a couple other things and it's all sorted now. Allthough stuffed if I know what caused it, but probably just needed to be reset after I cleaned the TB and IAC.

Part of the procedure for a throttle body clean is an IAC reset. Used to do this all the time when i worked at a Holden dealership. They would often be up round 40 steps before the clean, then back to 16 steps after.


Layto....