What can cause high tick-over? 2.1 dj.

[KarlT]

Hmmmmm. My 2.1dj has real high tick-over (1600/1900rpm).
Like it got a airleak or something.
From cold start...... Starts but idles badly, revs bounce between 500 & 1000 rpm. Give a bit of throttle, splutters but then picks-up & will rev freely.... But will now only slowly reduce revs down to circa 1800rpm.
Done all the usual timing checks, but very hard to adjust as revs all over place, replaced rubber vacume pipes, couldn't see any obvious problems. Is the a gizmo that is meant to regulate revs, that could be causing this outcome?

[HarryMann]

Does sound suspiciously like an air leak into the induction tract (weak hunting) Gizmo causing it, better someone else answers, maybe Aidan, Andy or a long-term DJ/MV owner

[1664]

What's it like once it's warm?

[KarlT]

Runs fine but high revs & slow to come down to the 1800rpm.
Obviously will overheat (fan coming on) in standing traffic.

[HarryMann]

Gradual onset or happened suddenly.. ?

Drippy injector(s) ?

Now sounds too much fuel from that descr. above

[KarlT]

Oh, now you've asked. I was hoping for a .... "Its this...." answer!!

Here we go........

Wife driving, a few weeks ago....... driving along fine, stopped at traffic lights, go to pull off, no power, slow tick-over, throttle makes no difference. Pushed to side of road.

She phones me. I get there, starts up fine, drives off.... Bl00dy women! I say!!

Week later, does same again, she phones AA. They turn up fiddle with things, Phone me, mention throttle tight? (seems fine to me) say oil pressure switch needs changing (ask which one he doesn't know there are two, again both seem fine to me). Anyhow they get her going & she gets home. Ever since we've had the high-rev situation above. But no low power, low tick-over problems.

[1664]

I was going to point the finger at the Idle control valve - have you tried unplugging it?

There is also however, the microswitch on the throttle valve the accelerator cable goes to - tells the 'brain' when you've taken your foot off the pedal.

You got a Haynes Manual?

[KarlT]

Is that the cylinder one on top of engine?
Yeah know about micro-switch. Can hear it clicking on/off don't know if signal is true though.
Haynes x2 & a bentley but 80/90 is so much better!!

[1664]

Is that the cylinder one on top of engine?

yes, it should vibrate and 'hum' when the engine's running. I can never hear the hum over the engine though so I touch the end of a screwdriver to it and place the handle in my ear. Try unplugging it, it's supposed to regulate the airflow depending on how warm the engine is (or isn't)

Yeah know about micro-switch. Can hear it clicking on/off don't know if signal is true though.

Yes, but there is a specific point it should switch at, see Haynes page 4B.4, picture 5.3. It's just a switch so a multimeter will tell you if it's working or not.
I know this is somewhat outlandish a suggestion but you could always try actually opening your "Haynes x2 & a bentley"

[KarlT]

How dare you!!!

[KarlT]

Problem is earlier fault was intermitant & now I can't seem to understand what would make it rev high.
Hmmmm... I think micro switch must be a goer.

[1664]

Won't do any harm to check it anyway. Try unplugging that control unit too.

[HarryMann]

aren't you supposed to bypass, connect the hoses together either side? or maybe not, but agree ISV and ISU alwasy worth a mention

[icosahedron]

The engine can only rev if it gets plenty of air so it is either an air leak, the throttle valve not closing properly or an open idle control valve.

An air leak means unmetered air and therefore not enough petrol with the engine wanting to stall.

The most likely cause is a tight accelerator cable or one that does not move freely anymore preventing the throttle valve from closing. When last was it changed?

It is easy to check if the ISCU or ICV is the problem by pinching the pipe to the ICV with your fingers and cutting of its air supply.

[KarlT]

By crikey, you may of hit on something.

Cable not been changed in my ownership & would explain poor running when cold, when cable has had time to slowly return & as soon as throttle used revs are jumping up.

From memory.... DJ Throttle body seems to have two separate movements. One arm for throttle cable & another for return spring. They seem to be able to move separately from each other.