4d56t high idle

[wazza87]

Hi fellas,
Having some trouble with my idle speed on the NG 90' paj. Worst part is its intermittent.

I have the idle screw on the injection pump set spot on at 750rpm. When warm it seems to idle higher around 8-900rpm but only every so often. I found that when using a large enough electrical load, the idle comes down to normal ie. Headlights on or windong up windows. Any ideas on where I can start troubleshooting? How can the electrical system be tied into the mechanical pump.

Thanks in advance.

[moose1178]

Complete guess.

Could it have something to do with the viscous fan clutch or alternator drive belt?
My understanding is the fan itself is meant to partially decouple at cool running temps and engage fully at a higher temp. So if the viscous clutch isn't working properly could the higher idle when warm be due to the unusual load from the fan going on to affect the other drive belts?

Then the idle could drop due to regular alternator load.

Being unfamiliar with the diesel (and after having a few beers ) a connection between temp and electrical load seems plausible to me.

[wazza87]

an interesting idea. how would I test this theory? I was thinking the pump is being "tricked" into supplying more fuel due to a fault. Maybe one of these random hoses from the alternator pump that runs to the IP or somethings had a leak. The fan is hard to turn when engine is off and moves more freely before start up when cold

[moose1178]

Soz

I was going to say something I thought was helpful, but that was with my petrol powered brain. I did a bit of research and the only thing I can think of is a vacuum leak, or possibly something to do with the A/C solenoid that steps up the revs when it's on.