Low idle on startup when its cold.
11-23-2002, 02:12 PM
#1
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Posts: n/a
Low idle on startup when its cold.
My son just picked up an 87 300ZX 2+2. Runs fine but one thing that he mentioned to me last night is when he starts it up first thing in the morning when its cold, for about the first minute or two he has to add a little throttle to it to keep it running or it will die. After it warms up just a bit its fine. I did a little reading in the Haynes manual that came with it ( it was still in the shrinkwrap) and came up mainly either a vacume leak or the air regulator. I'm not a neophite when it comes to working on cars but never worked on a "Z" before.
Am I on the right track or not?
Thanks
Paul
Am I on the right track or not?
Thanks
Paul
11-23-2002, 11:21 PM
#2
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Posts: n/a
Re: Low idle on startup when its cold.
It could be the vacumn lines, especially with all the heat under the hood for the past 16 or so years.
Start by looking at all the vacumn hoses and replace any that are hard, cracked or deteriorated. Then see how that works. If that doesnt do it, then try adjusting the TCV (throttle control valve) on the throttle body, mine is in bad shape, the upper screw to hold the TCV to the throttle body is broken off so while mine holds most of the time, it does tend to slip a bit and when it does, the car runs like garbage when it's cold, feels like it's missing, move the TCV to the right position and it's okay and smooth.
Start by looking at all the vacumn hoses and replace any that are hard, cracked or deteriorated. Then see how that works. If that doesnt do it, then try adjusting the TCV (throttle control valve) on the throttle body, mine is in bad shape, the upper screw to hold the TCV to the throttle body is broken off so while mine holds most of the time, it does tend to slip a bit and when it does, the car runs like garbage when it's cold, feels like it's missing, move the TCV to the right position and it's okay and smooth.
11-24-2002, 09:56 AM
#3
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Posts: n/a
Re: Low idle on startup when its cold.
I started by doing a cursory check on the vacume lines, and they didnt feel brittle or look cracked to me. I managed to look at it for only a few minutes though. Since he got the car I can't seem to keep him home long enough to really check it out. He's gotta show all his friends. He's 16, first car, saved his money just for the ZX. Cant say as I blame him. I alway wanted a "Z" when I was growing up, I'm 47 now, and I can sure see why all the folks in this forum love these cars. The little bit I drove it, it's a real hoot to have that kind of responsiveness and pep. I had a 71 Firebird when I was in college, but it never handled like my sons ZX.
Back to my problem though, there is no roughness to the idle at all, just slow idle on cold startup. After about 1 or 2 minutes its settles right down at 700 RPM. Thats why I was thinking it was the "air flow regulator" since that is what it does on cold starts. But sure will check all the vacume lines again and I open to any other suggestions.
Who nows, after I drove his car a little bit, I may sell the motorcycle and get a used "Z". Great little car.
Paul
Back to my problem though, there is no roughness to the idle at all, just slow idle on cold startup. After about 1 or 2 minutes its settles right down at 700 RPM. Thats why I was thinking it was the "air flow regulator" since that is what it does on cold starts. But sure will check all the vacume lines again and I open to any other suggestions.
Who nows, after I drove his car a little bit, I may sell the motorcycle and get a used "Z". Great little car.
Paul
11-24-2002, 11:06 AM
#4
Registered User
Join Date: Mar 2001
Location: Houston,Texas,USA,
Posts: 241
Re: Low idle on startup when its cold.
It does sound like the AR but could possibly be the CHTS ( cylinder head temp sender) needs to be replaced. There is a lot of good info on the 84-89 300zx at <a href=http://www.z31.com/ target="_blank">z31.com</a> but bring a thick skin and use the "search" feature when possible. Good luck.
ZenArcher
ZenArcher
11-29-2002, 02:11 PM
#6
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Posts: n/a
Re: Low idle on startup when its cold.
There is an easy AR check.
Take it off and put it in the refrigerator for 30 mins. then take it out and blow thru it. If you cant blow thru it, it's shot. Then, wait for it to warm up, there's a bimetal valve inside that should shut when it warms, if it doesn't close, it's shot.
Do yourself a favor, do a good tune up, change ALL the vacuum hoses,clean all the electrical connex you can see, and a new fuel filter. It'll save lots of headaches and give you much better performance.
Take it off and put it in the refrigerator for 30 mins. then take it out and blow thru it. If you cant blow thru it, it's shot. Then, wait for it to warm up, there's a bimetal valve inside that should shut when it warms, if it doesn't close, it's shot.
Do yourself a favor, do a good tune up, change ALL the vacuum hoses,clean all the electrical connex you can see, and a new fuel filter. It'll save lots of headaches and give you much better performance.
08-29-2014, 09:32 PM
#7
Registered User
Join Date: Aug 2014
Posts: 1
There is an easy AR check.
Take it off and put it in the refrigerator for 30 mins. then take it out and blow thru it. If you cant blow thru it, it's shot. Then, wait for it to warm up, there's a bimetal valve inside that should shut when it warms, if it doesn't close, it's shot.
Do yourself a favor, do a good tune up, change ALL the vacuum hoses,clean all the electrical connex you can see, and a new fuel filter. It'll save lots of headaches and give you much better performance.
Take it off and put it in the refrigerator for 30 mins. then take it out and blow thru it. If you cant blow thru it, it's shot. Then, wait for it to warm up, there's a bimetal valve inside that should shut when it warms, if it doesn't close, it's shot.
Do yourself a favor, do a good tune up, change ALL the vacuum hoses,clean all the electrical connex you can see, and a new fuel filter. It'll save lots of headaches and give you much better performance.
08-30-2014, 05:57 AM
#8
Registered User
Join Date: Oct 2012
Location: Edmonton AB Canada
Posts: 28
There is a screw on the idle up solenoid on drivers side of the plume that can be adjusted to turn up the idle. I purchased a block off kit from Intake Manifold Block-Off Plate Kit - 1984-89 Nissan 300ZX & Turbo | Acadiana Sports Car Orphanage - Official Store. And then used the small set screw on the throttle body, it's under the accelerator cable.
08-30-2014, 10:17 AM
#9
Registered User
Join Date: Aug 2013
Posts: 1,103
Cold idle rpms are controlled by the idle-up solenoid on the air regulator. Check out diagram EF&EC-4 in your factory service manual (you got it at XenonZ31 Reference for free!) Easy enough to test it with a multimeter. Take the solenoid out, apply current to the feeds and listen for the click - if it's working. 
If it isn't, I'm surprised you can idle at all. Should stall out right away if that solenoid is dead 
If it isn't, I'm surprised you can idle at all. Should stall out right away if that solenoid is dead
Last edited by zxguy1986; 08-30-2014 at 10:19 PM.
11-04-2014, 01:23 PM
#10
Registered User
Join Date: Nov 2014
Posts: 6
Same question what is AR?
Does anyone know what AR means? I am having the same problem my Z will needs throttle to start and hold for a minute then idle evens out. If there is no throttle it might start then die. Things I've checked are the spark plugs, fuel filter, lines that go to the fuel filter, throttle body sensor was also changed. None of those were the problem.
Last edited by sar82007; 11-04-2014 at 01:26 PM.
11-04-2014, 02:39 PM
#11
Registered User
Join Date: Aug 2013
Posts: 1,103
AR = Air Regulator. It has two solenoids and is a big deal in idle control. Your factory service manual ( available free at XenonZ31 Reference - if you have a Z31 
) shows it. The solenoids can be tested for operation with a multimeter. Check the one shown in your manual as Idle-Up Solenoid. They die eventually.
Meanwhile, do everyone a favor. Sign in, go to User CP menu (upper left), click Edit Signature and add your Z model, year, shifter, turbo or NA, etc. Saves you having to add it to every post. (Guys here go crazy if you don't lock your Q to your specific Z every time you post...They just ignore questions without enough info) Then click Edit Avatar and add a little Z pic under your nick. Cool. You are solid here
) shows it. The solenoids can be tested for operation with a multimeter. Check the one shown in your manual as Idle-Up Solenoid. They die eventually.Meanwhile, do everyone a favor. Sign in, go to User CP menu (upper left), click Edit Signature and add your Z model, year, shifter, turbo or NA, etc. Saves you having to add it to every post. (Guys here go crazy if you don't lock your Q to your specific Z every time you post...They just ignore questions without enough info) Then click Edit Avatar and add a little Z pic under your nick. Cool. You are solid here
Last edited by zxguy1986; 11-04-2014 at 11:05 PM.
11-04-2014, 04:45 PM
#12
Registered User
Join Date: Nov 2014
Posts: 6
Thanks
AR = Air Regulator. It has two solenoids and is a big deal in idle control. Your factory service manual ( available free at XenonZ31 Reference - if you have a Z31 ) shows it. The solenoids can be tested for operation with a multimeter.
Meanwhile, do everyone a favor. Sign in, go to User CP menu (upper left), click Edit Signature and add your Z model, year, shifter, turbo or NA, etc. Saves you having to add it to every post. (Guys here go crazy if you don't lock your Q to your specific Z every time you post...They just ignore questions without enough info) Then click Edit Avatar and add a little Z pic under your nick. Cool. You are solid here
) shows it. The solenoids can be tested for operation with a multimeter.Meanwhile, do everyone a favor. Sign in, go to User CP menu (upper left), click Edit Signature and add your Z model, year, shifter, turbo or NA, etc. Saves you having to add it to every post. (Guys here go crazy if you don't lock your Q to your specific Z every time you post...They just ignore questions without enough info) Then click Edit Avatar and add a little Z pic under your nick. Cool. You are solid here
11-26-2014, 05:22 PM
#15
Registered User
Join Date: Nov 2014
Posts: 6
RE: Magic
As great as that is it would seem I traded one evil for another. My heater doesn't work properly. When the heat is turned on the defroster and driver foot well are the only getting heat. The passenger side blows cold air. In another instance I'll turn the heat on and there is no hot air at all. I've researched this that it may be the watercock. Some people have zip tied theirs shut.
11-26-2014, 10:05 PM
#16
Registered User
Join Date: Aug 2013
Posts: 1,103
Yeah. Had the same prob for a couple of years with my '86na. I think it's a combo of the vacuum pump getting weaker and the damper doors slowing down/stopping. The zip tie thing works on the water ****. When you need AC, switch the zip tie in/out - I forget which. Did it every spring/fall for 5 years.
Best thing is to replace all your vacuum tubes for a start - before you replace pump(s) and take dash apart to clean dampers. If the tubes are leaking even a little, the system doesn't work right. Check out Thumper's analysis at Vacuum Lines Try to do it right if you can. (Tube diameters are a big deal in this) Take your time and do one tube at a time so you don;t screw up.
Best thing is to replace all your vacuum tubes for a start - before you replace pump(s) and take dash apart to clean dampers. If the tubes are leaking even a little, the system doesn't work right. Check out Thumper's analysis at Vacuum Lines Try to do it right if you can. (Tube diameters are a big deal in this) Take your time and do one tube at a time so you don;t screw up.
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