HELP!! increase in revs while ideling

[shaunh]

when i start my car hot or cold it seems to rev at random speeds varying from 400! to 1800 :/ any ideas as to what it might be?
any help is greatly appreciated

[Grizzly]

Petrol, diesel or LPG? I had a similar thing happening with my LPG and it turned out to be due to the mixer mechanism not sitting flush on the carby and excess air stuffing things up.

[shaunh]

sorry about that, its a 4.2 petrol carb manual 89 maverick

[Silver]

either right foot straying too close to right pedal, or a vac leak somewhere, would be my guesses. But 1800 sounds a lot.

[shaunh]

I dont touch the throttle at all when I start the car, key in the ignition and turn, fires up first go everytime just the idle revs are all over the shop

[Silver]

sorry shaunh, my comment re right foot was meant to be a joke, no offence meant :-)

[shaunh]

None taken mate, just clarifying

[Silver]

apart from the idle going up and down, does it respond normally to the accelerator pedal? Put another way, when you depress the accelerator to make it do say 1000 rpm, or 2000 rpm, does it stay steady or move up and down by a big range of revs?

Is the distributor bolted down tight? Carby?

[Silver]

I think the manual says to depress the accelerator once for cold starts. I think this is so the auto choke can allow the choke butterfly to close. I don't understand the auto choke on the TB42 - a combination of vacuum and electrical bits for the fast idle etc. Luckily the mechanic over the road does, and helps out. It may not be a good sign that he has taken his choke out altogether :-) Note though, that we live in Brisbane where 2 degrees C is a cold morning :-)

[nowoolies]

this is gunna sound dumb
but in my old t.tt.t.tt.t.. still cant say it
the spring broke on the throttle peddle and tangled up on its self so it would sorta work and then again it did`nt
my rev`s on start up were all over the place , but i did`nt notice any differant when driving
just a thought

[taslucas]

How long does the idle stay high? Does it return to normal idle after a quick jab of the throttle? If it does then it might have something to do with the auto choke.
Is it only when you start up or does it rev high after driving for a while?

[steelo]

My rb30 does similar stuff, but when it warms up (time can vary) it runs normal. I've also removed the fuel warmer "net" from the carby (in the poly/plastic plate) but & also widened the spray chamber just at bottom of chamber as the last 2 cyl/plugs didn't seem to be getting the same amount of spray/fuel.

[pearcey]

Hi Shaunh.
There is a small spring between the choke fast idle cam and the carby body which if fitted incorrectly will catch the cam and cause irratic ideling.

[thebeatjackson]

you've probably sorted it by now,
is your hand throttle all the way in? my revs vary when I use that, not quite from 400 to 1800, more 500 to 1000, I'm doubtful that that's the cause, but worth a check. by hand throttle I mean this
http://www.nissanpatrol.com.au/forums/showthread.php?8054-What-does-this-lock-button-do&highlight=lock

[the ferret]

Sticky throttle cable, loose carby, sticking butterfly in carby, sticky choke mechanism, vacuum leak, faulty PCV .worn butterfly shaft.
Cheers, the ferret.

[johno90]

revs go up and down at idle = hunting = leak in manifold, easy way to check is get something like t/b cleaner and spray around all contact areas if revs change when spraying at a certain spot theres your leak :)

[saw13]

Might possibly be the carby needing an overhaul, i had this problem in my old 91 GQ nd it fixed the problem, then i converted it to EFI lol

[Robo]

Get yourself a manual and start checking for something wrong on carby by the specs given.
I'm leaning towards what pearcey said about the spring, possibly even broken.
there's something funny going on around this area.
but it really should be a pain to start if you don't touch the acc pedal to start especially cold starting.
that's how choke is engaged, you have to push a little to activate auto choke.
cheers

[HammerBuilder]

So how'd you go shaun with your rev problem is it sorted now or are you still playing? Also check your vacuum hoses for leaks even down to the hose from the rocker cover to the inlet manifold. anyway see how you go & let us know whats happening.

Cheers Tony