Idle speed goes up when radiator fan turns on

[colorfull]

Hi,
On my 87 Syncro, the idle goes up to 2000rpm as soon as the radiator fan kicks in. It goes back to normal when the radiator fan os not running.

Any idea why?

The van have had the AC removed by a past owner.

Thanks![/b]

[colorfull]

Any clues?
So far I changed all the sensors (power steering, temp2, 02)
Everything listed in the Digifant manual checks out as well.

[MarkWard]

Has all of the AC been deleted including the wiring? When the fan kicks on the load on the alternator should actually load the engine. I don't have a manual handy, but it is not uncommon for other vehicles to increase idle to account for load of ac compressor. It's a stretch, but maybe the vanagon air had a provision to tell the ECU the air is on and that is what is happening when the rad fan clicks on back feeding power into the AC wiring. The diagrams can verify the guess

Another possibility is the idle is at the edge of the spec that the IAV can handle
and maybe simply adjusting the idle speed would help. I would also check the TPS adjustment.
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[colorfull]

Thanks Mark,

Yes the AC has been completely deleted, including the compressor and wiring.

You might be right about the idle being at the limit of what the IAV can handle, as it is right at 950 on cold starts but jumps to 1300ish after long drives. Adjusting it any lower makes the van hard to start when cold.

I will nonetheless verify the wiring diagram as well to see how AC and radiator fan interconnect.

Thanks a lot for your input!

[Wolfsburg 92]

Hello Colorfull,

We have 2 vans with the same problem. Have you found what was wrong?

Francis