High Idle

[MKPatrolGuy]

Got a weird prob with Dad's 89 Petrol GQ, when you are driving along and back off the throttle the revs wont drop below about 1200-1400 rpm Even if you shift into neutral and coast to a stop the idle stays high until you completely stop, then it drops to 600-800 rpm.

Anyone know why it does this?

[Thor]

seems a lot of people have idle issues. here is a possible solution:
check the vacuum leak between the upper and lower intake
manifolds. check that the gasket has not been sucked in and distorted over time.
does it have a/c?

[MKPatrolGuy]

will check the gasket,

No it doesn't have a/c

[V8Patrol]

easiest way to check for vacum leaks is to spray small quanties of "areostart" around the suspect areas.... if there's a leak then the motor's rpm at idle will alter slightly. Check every where there is a vacum point , and dont forget vac assit brake boster/hose, carby to manifold join, manifold to head, any other vac points.
Also if it has aircon there is a small module usually on the carby linkage setup that increases the idle slightly when the aircon is operating, the aircon draws a fair amount of horse power at idle and in some smaller motors will actually stall the motor if this module has failed. These modules are generally vac operated aswell.

[Ryan]

mine has exact same prob, 88 petrol with air con, let me know if you fix it cause ive looked all over it and cant find any problems, its annoying tho and wont stop until the caris completely stopped then they drop back down to idle


Cheers

Ryan

[hazard]

When I was working at Nissan I vaguely remember replacing carbies under warranty (factory recall), does anybody remember what the problem was and if it is related to the fast idle... It was 10 years ago and my memory is very blurred, but there should be a bulletin on it...

[bazzle]

Check fast idle cam, on RH side under carby, sticks, lube with teflon spray

Also decel valve on other side.
Bazzle

[M queue]

I had the same problem in my L28 MQ, after lotsa searching on the net i found the fix.

On ya carby there (on mine anyway) there's a rubber grommet/plug, pop it off and you will see a small grub screw, unwind this.
I had to unwind mine almost 4 full turns before i got it to idle properly.
Unwind it 1 turn at a time, take it for a drive, if it still does it repeat the process.

From what i can gather it's the high speed idle.
This thing is hooked up to the speedo and gear box to supposedly stop stalling when pulling to a stop.

Hope this help's...

Tom

lol....i just noticed the original post date....ooops. Tad late.

[patrol man]

the carby rework form nissan was to fix a problem with the seconary not opening early enough, adjusted vaccum port. the fast idle adjustment sounds like the go, as this is related to the speed . bcdd valve? this has somthing to do with poplution control as it stops the idle droping to low while still at high revs, ie still lets air in to reduce rich fuel mix under deaccleration. this may need adjusting as mentioned before.

[marin]

had same prob on mine, sticking at 1200 ish cept that every so often it would stick at around 2500RPM! mine was a sticky fast idle cam, it was moving past all the steps in the cam, and sticking further around

[bazzle]

That what I said..

Bazzle

[CJ Burns Esq]

In auto's and 3.0l petrols there is a dashpot that stops the idle from dropping too soon. That also causes the problem.

[mkpatrol]

Im with Bazzle, sounds like the decel valve is adjusted incorrectly, Mazdas/Fords do it all the time. People adjust this screw thinking its the idle adjustment.

[MKPatrolGuy]

Im with Bazzle, sounds like the decel valve is adjusted incorrectly, Mazdas/Fords do it all the time. People adjust this screw thinking its the idle adjustment.

Just digging this up from the dead as I'm currently driving Dad's Patrol and he hasn't bothered getting this problem fixed.

How do I adjust the Decel Valve?

[mkpatrol]

Various ways, they can have an adjustable rod or the whole unit turns inside the bracked & there is a lock nut to retain it.
Back it off until it doesnt do anything. Wind it on a little it a time until it holds the trottle up for about 2-3 seconds, any longer & it will keep the revs up. It should be vaccum operated so when you are driving they will hold the throttle up for longer until the engine is back at idle & then it should take the same time as you set to come back to idle properly.

If you have any more problems let me know.

[buger man]

I had the same problem in my L28 MQ, after lotsa searching on the net i found the fix.

On ya carby there (on mine anyway) there's a rubber grommet/plug, pop it off and you will see a small grub screw, unwind this.
I had to unwind mine almost 4 full turns before i got it to idle properly.
Unwind it 1 turn at a time, take it for a drive, if it still does it repeat the process.

From what i can gather it's the high speed idle.
This thing is hooked up to the speedo and gear box to supposedly stop stalling when pulling to a stop.

Hope this help's...
i would bet my left b that this is the problem as i have fixed 4 or 5 with the same problem

Tom

lol....i just noticed the original post date....ooops. Tad late.

[MKPatrolGuy]

Thanks Guys, I will have a look tomorrow.

[steelo1]

In auto's and 3.0l petrols there is a dashpot that stops the idle from dropping too soon. That also causes the problem.

Old post I know, but doe's anybody know where this is, ta.
I have an rb30 manual & when air-con is on it seems to idle between 1200 & 1400rpm & sounds quite fast. It normally idles at around 750rpm.

[CJ Burns Esq]

In auto's and 3.0l petrols there is a dashpot that stops the idle from dropping too soon. That also causes the problem.

Old post I know, but doe's anybody know where this is, ta.
I have an rb30 manual & when air-con is on it seems to idle between 1200 & 1400rpm & sounds quite fast. It normally idles at around 750rpm.

I will have alook in the manual later tonight and see fi Ic an get an answer for you.
CJ