1989 series 1 VN V6 Auto Rev issues

[Callumbh5]

Hey team,

Yet another problem has popped up with the VN lol.

Okay so I noticed the revs don’t drop as much and it tends to tug me along in drive faster while coasting around the car park or into my driveway quite quickly on its own.

with a small stab of the throttle it’ll drop down to normal.
It also changes down gears more noticeably than I remember when braking.

When this problem is occurring and I pull over and put it in neutral it'll rev to about 1500 - 2000 on its own until I give it another small stab on the throttle.

Things I’ve recently replaced before this problem arose:

IAC
TPS
CAS
FPR - fuel line & vacuum line
MAP sensor vaccum hose.
Radiator.
DFI and Coil conversion.
New spark plugs & leads.

Any ideas? Help would be greatly appreciated.

Cheers

 

[Callumbh5]

Okay so I noticed the revs don’t drop as much and it tends to tug me along in drive faster while coasting around the car park or into my driveway quite quickly on its own.

with a small stab of the throttle it’ll drop down to normal.
It also changes down gears more noticeably than I remember when braking.

When this problem is occurring and I pull over and put it in neutral it'll rev to about 1500 - 2000 on its own until I give it another small stab on the throttle.

Things I’ve recently replaced before this problem arose:

IAC
TPS
CAS
FPR - fuel line & vacuum line
MAP sensor vaccum hose.
Radiator.
DFI and Coil conversion.
New spark plugs & leads.

Any ideas? Help would be greatly appreciated.

Cheers

Hey team,

Yet another problem has popped up with the VN lol.

Okay so I noticed the revs don’t drop as much and it tends to tug me along in drive faster while coasting around the car park or into my driveway quite quickly on its own.

with a small stab of the throttle it’ll drop down to normal.
It also changes down gears more noticeably than I remember when braking.

When this problem is occurring and I pull over and put it in neutral it'll rev to about 1500 - 2000 on its own until I give it another small stab on the throttle.

Things I’ve recently replaced before this problem arose:

IAC
TPS
CAS
FPR - fuel line & vacuum line
MAP sensor vaccum hose.
Radiator.
DFI and Coil conversion.
New spark plugs & leads.

Any ideas? Help would be greatly appreciated.

Cheers

So I’ve taken apart the throttle body and cleaned it including IAC and TPS, IAC had some slight soot on it but nothing crazy, TPS had a little oil on the inside which is now cleaned, and I thoroughly cleaned the throttle body out with a tooth brush and some TB cleaner, gasket also looked fine which was replaced not long ago when the thermostat was done.

I had also cleaned the spark plugs with a wire brush just to be sure

After this I put it all back together, reset the computer then done the reset IAC process. I took it for a decent drive and noticed it didn’t feel like it was revving for me while coasting.

But once I got home and out into park it jumped to 1200 revs again which is less than usual but still odd, it went back to 900 after about 10 seconds.

 

[Immortality]

Have you adjusted the butterfly stop screw at all?

The earlier V6 motors (VN-VR) need to have the idle reset, to do this, once the engine is up to temp, hold the engine at 2000rpm for 20 seconds IIRC (I can't remember the last time I did this). This forces the ECU to reset the idle.

 

[Callumbh5]

Have you adjusted the butterfly stop screw at all?

The earlier V6 motors (VN-VR) need to have the idle reset, to do this, once the engine is up to temp, hold the engine at 2000rpm for 20 seconds IIRC (I can't remember the last time I did this). This forces the ECU to reset the idle.

I haven’t touched it at all.

Oh I assumed I had to reset idle by sitting at 3000 for 8 seconds, so beat to sit at 2000 for 20 seconds? I’ll do that tonight because after driving to work this morning it has gone back to how it was

 

[Having A Break]

.

 

[MikeC]

Yep. Your cable and its adjustment are well worth a look. The IAC has to be fully retracted when it's installed. Watch out for el cheapo knock off IAC's- they look the same but just don't work. After wasting time and effort on a cheap ebay item I bought a Delphi -at the time Delphi had taken over the GM parts division.