vn rough idle

[Garth]

as we all know, i got me a vn, now this is the question i have got

when i change gear's i.e. from drive to neutral, the idle drops way down, it sounds like it's gonna stall, then it pickes up,

when in gear, at traffic light's, it apear's to make a coughing sound. it's a very rough idle, i look at the tacho, and it's sitting around the 700rpm mark,

history of work done so far, new ecu new filters', and injectors, what else could be going on here guy's, i feel as if im missing something easy, coil pack is fine, spark plug's and leads are fine, dfi moduel is fine, cas is fine, map sensor is fine, fuel reg is fine, no fault codes are pressent, what am i missing


cheers
garth

p.s. help me, i dont wanna be driving the bloody ba falcon anymore than i have to

[The1985divo]

Id have a look at the trannie fluid, might be as simple as that

When my VN idles roughly the oil is usually low and once i top it up all is fine.

[jdd]

Possibly IAC valve ?
If you don’t mind me asking, how do you know the DFI module and coil-pack/coils are ok ?

[AirStrike]

Garth would be the best one to ask about the DFI module (I can find it if you want but cant be bothered) but the Coil Pack can be checked using a multi-meter or ammeter and measuring the primary and seccondary resistance of the coil.
If you need more detail just ask
Cheers

[jdd]

Thanks, but I’m well aware of how to test DFI modules & coils.
I was interested in what test(s) Garth had done in order to verify they were ok. Not all tests are 100% guaranteed (i.e. testing the primary or secondary resistance of a coil-pack with a multi-meter is not a 100% guarantee that it’s ok).

[AirStrike]

Well thats the only way to test em champ (as far as I know of, any one else??) and it is a fairly accurate way to check....
Cheers

[jdd]

Testing the primary and secondary resistance of a coil with a mutli-meter is a good basic test to make sure it’s not burnt out. This test does not 100% guarantee the coil is ok. It cannot detect a coil with poor performance, intermittent operation or one that fails (totally or intermittently) when hot only.

[AirStrike]

Good point mate.....

[rebel]

If you don’t mind me asking, how do you know the DFI module and coil-pack/coils are ok ?

JDD- I have known Garth for only a short time (almost a year,) we actually met through this site as I had problems with my VN back in January, Garth has completed an auto elctricians course, maybe a few years ago, but so far every thing electrical that has gone wrong with my car, it has been SuperGarth to the rescue, sometimes only bringing his Multimeter along, but he also has access to a SCAN tool and other ALDL ridgey machines and computers that I never knew existed, so DFI and Coil packs being an electrical issue I am quite sure that if the car was suffering symptoms of them being a problem, he would have checked them for sure...

[OSL-060]

Other than vacumn leaks, give what JDD said a go. Take the throttle body and elbow off, take out the IAC and clean the whole lot with a product like Nulon Throttle Body and Carby Cleaner. You'll be amazed at the blow by, carbon and other amounts of sh!t that come out of it. Try not to be too fussy, they aren't exactly known for their silky smooth idle but cleaning should improve things a little. Adding not removing a bellmouth if it's a series 1 will also flatten the idle out a 'bit'

[jules]

yep, i 3rd that, IAC valve. i believe it's the IAC's job to lower idle speed after trans load is removed when you shift into neutral. sounds like it's struggling with that, as jdd/jake said due to sh*t inside.

[kuffy]

my vp has been idling badly also recently. I found there was a small petrol leak at the connection of the fuel hose and the fuel rail (the right bank of injectors). So i tightened the hose clamp and no more leak. Also, my car runs on gas...or it used to, not anymore. So this morning I started playing around with the screw on the converter, and the car backfired through the air intake and blew a big hole in my airbox, with my face almost right over the airbox. it scared the hell outta me Instead of replacing the airbox i just put one of those cheap airpods on. since i was at the air intake, i decided to clean out the throttle body. I used the nulon throttle and carby cleaner. Sprayed it all in..and gave it a quick scrub with a cloth. Now my car idles as smooth as silk on petrol...even when the engine is cold and hot. But on gas now, it only idles when the engine is hot, ill get the mechanics to fix it for the cold. My guess is that when i cleaned out the throttle body, it sucked the cleaner into the IAC valve and cleared any blockage that was in there making it struggle for air.