Fluctuating idle

[Hilux]

Recently I`ve noticed that the idle speed can fluctuate occasionally. When purchased it was rock solid 900rpm but recently is nearer 1000 which I didnt have an issue with.........but.................

It now can fluctuate occasionally idling at 1200 and dropping slowly. It can also `hold` the revs as you come of the throttle at about 1200-1400 and then suddenly drops them or the revs come down slowly rather than if you were engine braking.

What could be causing this?

 

[eastendr]

Idle speed valve sticking - lots of carb cleaner to give it a good soaking.

Do you have the vapour purge system fitted ? There's a trick to disable the valves that can cause the idle to bounce between stalling and 1200 RPM.

Rick.

 

[Hilux]

Hi Rick

Now you post I recall a thread regarding this but a search on `idle speed` only brings up this thread?????????????

Where is the idle speed valve?

Have I got the vapour purge system?

 

[eastendr]

The good news is that you haven't got a vapour purge system []

The idle control valve is mounted below the inlet manifold. Look between runners 2&3 and you will see it. It has two thick rubber pipes. One goes to the inlet manifold union between runners 1&2, the other goes to the 'J' pipe.

It's the thing bolted to the block in the middle of this picture http://www.cannell.co.uk/images/Cannell_web/944T%2041%209.jpg and more detail here http://www.cannell.co.uk/images/Cannell_web/944T%2049%203.jpg.

You can disconnect the pipe from the 'J' pipe and use the engine's vacuum to draw the carb cleaner in. But be careful ...

HTH

Rick.

 

[Fen]

ORIGINAL: Hilux

Hi Rick

Now you post I recall a thread regarding this but a search on `idle speed` only brings up this thread?????????????

Where is the idle speed valve?

Have I got the vapour purge system?

Somebody doesn't have this year's "must have" accessory; a new expansion tank []

 

[Hilux]

Somebody doesn't have this year's "must have" accessory; a new expansion tank []

Hi Fen,

1) I`m not a dedicated follower of fashion
2) If you cant see the water level you dont worry about it []

On a more serious note, HTF do you gain access to the idle valve/J pipe you obviously dont have to remove the manifold if Rick is correct?

Whats the issue with using carb cleaner when the engines running? explosion?

 

[Hilux]

The good news is that you haven't got a vapour purge system []

Is it? Why? and why dont I have/need one?

Just a thought? Is the purge sytem a canistery type thingy positioned where the ABS cabley jointy thingy is on each top inner wing thingy?

 

[eastendr]

ORIGINAL: Hilux

The good news is that you haven't got a vapour purge system []

Is it? Why? and why dont I have/need one?

Just a thought? Is the purge sytem a canistery type thingy positioned where the ABS cabley jointy thingy is on each top inner wing thingy?

It's one of those things to keep the Californians happy, but of no real world use. Deletion is acceptable and removed yet another load of possible vacuum leaks []

It's in the lower right corner of this picture

Rick.

 

[eastendr]

ORIGINAL: Hilux

Somebody doesn't have this year's "must have" accessory; a new expansion tank []

Hi Fen,

1) I`m not a dedicated follower of fashion
2) If you cant see the water level you dont worry about it []

On a more serious note, HTF do you gain access to the idle valve/J pipe you obviously dont have to remove the manifold if Rick is correct?

Whats the issue with using carb cleaner when the engines running? explosion?

Remove the top of the airbox / snorkel. You should then see the thick pipe coming from under the inlet manifold to the J pipe. You may have to remove the hard pipe as well - can't remember that far back ...
Carb cleaner is very potent stuff and extremely flammable. When it gets in the intake you will find the revs will rise and there may be a possibility of a backfire if you use enough / too much [].

I'd be inclined to remove the rubber pipe from the J pipe and block the J pipe port. Then squirt carb cleaner down the rubber pipe and start the engine. The carb cleaner will be sucked through to the idle speed valve by engine vacuum ... you may want to repeat a few times to give it a good clean. Over time a varnish forms and prevents the internals moving smoothly hence large jumps and consequent stability problems with the idle.

Rick.

 

[Indi9xx]

I would be inclined to say that it could be that the idle and mixtures need setting up. This should be done during a service if propper trained staff do it )

If you get the chance to swing past our workshop we will do it for free for you.

It could be the idle control valve, but again dissabling the ISV and setting it up will diagnose this.

 

[edh]

It may be that the TPS isn't clicking off when you come off the throttle - easy to test as you can hear the clicks

I had a problem with this - occasionally the revs wouldn't drop when off the throttle & clutch in. It can be the slightest of adjustments - maybe a matter of 2 or 3 mm

Clarks garage has a section on this and idle speed adjustment. As Jon says - this also covers disabling the ISV (just jumper 2 points on the diagnostics port)

 

[Guest]

I had the same problem on my '85 - and no amount of tweaking the idle would erase it - had to set it at 1K in order to over-ride the fault. I eventually discovered it was simply a poor ground twixt the thick copper braided strap and the engine firewall. Cleaning this up solved the problem completely.

A quick check to see if this is your problem is to take the car round the block to get the engine up to working temperature, stop the car and (engine running) clamp one end of a booster cable to the negative pole of the battery and the other end onto a good clean earth directly on the intake manifold. If the RPM increases a couple of hundred and holds steady you've found the problem. If it doesn't try clamping a screwdriver to the cable and probing directly onto the smaller grounds (thick-ish brown wires) at the back of the manifold.. If the RMP picks up it means you need to clean under the connections. If that doesn't locate the problem try clamping the cable twixt battery and bulkhead.

If none of these work you might check out the connection blocks for engine sensors and the engine speed sensor gap off the flywheel starter ring.