VN v6 runs bad

[1989vn]

I have a v6 in my vn and it seems to have a bad idle when hot .It runs good when cold. I have had it checked over buy mechanics .Every thing is good no one can find any thing wrong with the engine .The compressions are good ive replaced the injectors, coil pack with vp--vs parts. I have done the fuel pump and filter.Nothing i do gets rid of that bad idle .Can any one tell me if there is something else it could be? Also i want to put a genuine cold air intake on i want to ask when i do do i take the rubber strip that is under the front edge of the bonnet off? Any help will be very apprecieted. Thank you
Its a manual .

[frdhtr]

Worst case is the valve seat in the heads is slightly burnt through, generally still runs fine just has a bad idle usually on LPG high km engines is your car like this? Also my vp like a typical commodore used to run rough after sitting at the lights for 3 mins or so, when I did my inlet manifold gasket I pulled apart my litters and cleaned them and it idles much better now, cheers

[pow3rslave]

dunno that it'd be worse when hot, but i'd be cleaning all the gunk out of the IAC on the throttle body. if it's blocked it won't breath great with the throttle closed

[m1chael1o1]

maybe you alternator is on its way

[wortus]

dunno that it'd be worse when hot, but i'd be cleaning all the gunk out of the IAC on the throttle body. if it's blocked it won't breath great with the throttle closed

I'd giver this a go as well but make sure if you use throttle body cleaner not to immerse or spray a heap onto the IAC or TPS. Best to remove the throttle body and take off these parts then clean it.
Also if it is an early VN you could try fitting the bell mouth fitted to later models however some posts I have read said that it may reduce the performance slightly. It was I think fitted to improve idle by trying to give a more even flow of air to each cylinder.

[1989vn]

Hello
Thank you for getting back to me.Forgive my ignorense What is the IAC and TPS and where are they ? And what is the bell mouth and where is that? Again thank you for your help.Cheers

[1989vn]

Hello
Thank you for replying.My engine has never been on gas but it has alot of kms on the clock But my mechanic showed me as we did a compression test together and my comps are 160--170 psi. I did do the manifold gasket but i didnt think to clean the lifters. My engine runs very nice when cold But when its warm it gets the crap idle.Again thank you

[Not_An_Abba_Fan]

I'd be checking the O2 sensor as well, when cold they run in open loop mode, so it won't affect it, but once warm the ECU adjusts the air fuel ratio according to the signal from the sensor, if the sensor was buggered, it may cause a bad idle when warm.

[frdhtr]

How bad does it run? Like a continuous misfire or like a minor rough idle- vibrating feel, does it dissapear straight away when you accelerate? You will be able to hear it the best at the rear were the exhaust ends and decipher if it's like a popping sound or a miss fire. Also have you had the computer checked for error codes and do you have an engine light on? Also does it have the series one square coil pack, they are prone to run rough. Cheers.

[pow3rslave]

Hello
Thank you for getting back to me.Forgive my ignorense What is the IAC and TPS and where are they ? And what is the bell mouth and where is that? Again thank you for your help.Cheers

the iac is the inlet air control, basically a valve that's there to bypass the throttle butterfly and makes sure the engine gets air even with it close, they can get gunked up over time.
the tps is the throttle position sensor, which is there to tell the computer what state the throttle butterfly is in, as with the iac. i don't know that these get gunked up, but you might find they wear out etc. if they do/can be cleaned then go for it, there'll be someone who's done it before, possibly with a guide.

[1989vn]

Hi Mate .Thank you.Can you tell me please were are these parts? Cheers

[1989vn]

Hi frdhtr .Thank you for helping. Its a minor rough idle not realy a miss fire and it does dissapear when i accelerate.The exhaust note isnt smooth. The engine goes good it flys when i drive and change threw the gears.The coil pack is the VP type leads on one side.My mechanic checked the computer he did find the cold air senser was stuffed he replaced that. But it didnt fix it. No engine light comes on. Cheers and thank you.

[pow3rslave]

Hi Mate .Thank you.Can you tell me please were are these parts? Cheers

they're both on the throttle body, the tps will have a couple of wires coming off it, not 100% on the IAC, i don't have my v6 anymore. a gregories manual will lay it all out.