VN V8 idle issues

[VN_SS_CM]

Vn ss 5.0

Hey guys vn keeps on stalling intermittently when slowing down, idles up and down between 200rpm 1300rpm sometimes it will idle ok I have to have to set it at 1000rpm anything less and it idles all over the place it has a cam, new iscv, dizzY, leads, throttle body cleaned out base idle reset procedure done idle is worse with ac on aswel!

 

[CALMAN]

Have you check for error codes?
But I am thinking its 1 of 2 things or both. Idle air controller or Throttle Position Sensor.
My car was doing the same but from 500 to 1000 rpm, I have replace the throttle position sensor now it is running great.

 

[VR38]

^ agree with above.
Side note, be careful taking logged fault codes as a tested fact, a sensor can go out of spec and still be present as operational to the ECU.
The ECU will only log a fault code if the sensor fails of is out of range.

 

[VN_SS_CM]

also another thing that happens If I use the car and let it sit for say 2hours plus then go to start it I cranks over for awhile before kicking in.....hoping to score a banana manifold complete with injectors and throttle body tonight for testing

 

[Cheap6]

How big is the cam? Was the MemCal rewritten to suit it? If you've changed the manifold vacuum signal with the cam the air:fuel mixtures will be off. There's only so much the ECM can learn around.

If it's not related to the cam, these engines are known for having vacuum leaks past the inlet manifold gaskets.

A dead speed sensor can also cause idle problems. The speed sensor fault codes rely on relating MAP sensor voltage to the road speed indicated by the Vehicle Speed Sensor. It's possible the VSS is intermittent enough to not set a fault code or that the altered vacuum characteristics due to the cam makes it less likely for the speed sensor fault conditions to be present, so the code is less likely to set.

 

[VN_SS_CM]

ok guys thanks for the help

Managed to sort of narrow down this problem.........the idle goes up and down between 200rpm - 1200rpm approx only when aircon is on or whilst turning left or right on the spot with aircon off also does it worse with it on.... but let her sit there and it idles fine....its got a Crane Cam 884301

 

[VN_SS_CM]

oh and its got a another memcal as its fitted with a knock sensor

 

[Cheap6]

With the new IACV, was the 'O' ring replaced?

Is there an intermittent wiring connection between the IACV and the ECM? You might see if you can get the idle to change by wiggling the IACV wiring.

Still could be cam related.

 

[VN_SS_CM]

yep brand new iacv with seal...hmmm im wondering I looked back thru videos of then I had the car running it never did this so it must of been something ive done lol.... could it be due to a lower degree thermostat? i put a 160deg in there.....as from cold start this morning it ran like a bucket of **** felt like it had a miss...backfired hmmmm

 

[yxyx64]

never mind .............