Topic: Nissan Fast Idle Problem

[etype_mini]

My 1985 Nissan Pulsar e16 engine has recently started idling at ~2500 rpm (only when moving). When I come to a complete stop it idles normally. I'm really perplexed, and my workshop manual makes it difficult to diagnose as there are many configurations of the carb (Calformia, UK models etc) I had an inkling it was the "dashpot" which is a doohicky that is supposed to decrease the sudden deceleration when accelerator was realeased. I seems to work fine in the driveway (Fast rev and release...takes ~2 seconds to go back to idle instead of cutting back revs quickly)
It's very very odd though, if I'm travelling at any speed and depress clutch "idle" is 2500 rpm, as soon as I stop moving idle is fine at 900-1000rpm.

[barrie1]

Etype Mini Welcome to the Forum, I would be checking the return spring on your carb to start with and then spray cleaning the outside with a good choke cleaner, inside and out and let soak for about 10 minutes and then refire the engine.

[etype_mini]

I have WD-40'd all the linkages and springs on the outside. You mention "inside and out" ?
It's the strangest thing...I can roll up to a stop light in neutral and it's at 2500rpm, as soon as I actully stop moving it drops back down to 1000rpm. I dont know how it knows...but it does...it's like it's tied in with the wheels, as daft as that sounds.

[Roadrunner]

I'm just guessing here Barrie, but would a damaged idle adjustment screw cause this problem?

[Sterling]

A longshot, but could it be some mechanical problem with the idle mechanism where the weight transfer of stopping affects its position?

[barrie1]

You may have answered this question already by yourself Etype. You must never ever use WD40 on a carberator as the fluid only draws more dirt and stickie mess then before. It has a magnetic base to it and should never be used anywhere's near a carb. Yes a Damaged Idle adjustment screw would certainly give you a hard time. Get a Can of the proper Carb Cleaner and redo this spray job as the WD40 is doing more harm then good on there. I recommend the Carb Cleaner from a GM parts counter as it is the only one where the engine will actually run just with this. Handy for a dead fuel pump to move a car a few feet into the shop or similar thing.

[wgeg]

I think you have a vacuum problem, check for a defective vacuum diaphram.  Possible in the heater or a/c controls under the dash.  If you car has a vacuum canister to balance instruments, it may be leaking.