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High Idle
Posted: Tue Oct 14, 2003 12:42 pm
by 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?
Posted: Tue Oct 14, 2003 1:16 pm
by 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?
Posted: Tue Oct 14, 2003 1:24 pm
by MKPatrolGuy
will check the gasket,
No it doesn't have a/c
Posted: Tue Oct 14, 2003 1:28 pm
by 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.
Posted: Tue Oct 14, 2003 3:17 pm
by 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
Posted: Tue Oct 14, 2003 6:22 pm
by 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...
Posted: Tue Oct 14, 2003 7:55 pm
by bazzle
Check fast idle cam, on RH side under carby, sticks, lube with teflon spray
Also decel valve on other side.
Bazzle
Posted: Sun Jun 13, 2004 11:13 am
by 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.
Posted: Sun Jun 13, 2004 11:54 am
by 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.
Posted: Mon Jun 14, 2004 10:26 am
by 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
Posted: Mon Jun 14, 2004 12:45 pm
by bazzle
That what I said..
Bazzle
Posted: Tue Jan 11, 2005 1:08 am
by 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.
Posted: Tue Jan 11, 2005 7:47 am
by 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.
Posted: Thu Jun 09, 2005 1:42 pm
by MKPatrolGuy
mkpatrol wrote: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?
Posted: Fri Jun 10, 2005 1:44 pm
by 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.
Posted: Sat Jun 11, 2005 3:34 pm
by buger man
M queue wrote: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.
Posted: Sat Jun 11, 2005 11:23 pm
by MKPatrolGuy
Thanks Guys, I will have a look tomorrow.
Re:
Posted: Wed Mar 02, 2011 1:12 pm
by steelo1
CJ Burns Esq wrote: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.
Re: Re:
Posted: Sat Mar 05, 2011 11:12 am
by CJ Burns Esq
steelo1 wrote:CJ Burns Esq wrote: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