EZee

I'm having an issue with the idle speed on my '86 NA 5 spd. It starts and runs fine, but the idle speed seems to wander when it's warmed up. It's been tuned up with OEM parts (plugs, wires, cap, rotor, PCV, IAC) and I set the idle speed using the FSM procedure. It seems if I rev it to 2000 for a minute or two, the idle settles right at 700. When I drive it and come to a stop it will be as high as 900, or as low as 550 and act like it wants to stall. My initial thought was a vacuum leak, but I haven't found anything.

csgt428

Mine (86 NA) idles at 1100 anymore when it's warmed up Never used too...still gets 30mpg hwy....

donr1494

A common problem on these is the little rubber sleeve on the end of the throttle cable right art the throttle body. It comes loose and jams, holding the blade open at times. If it won't stay in place, just remove it. Be sure the cable has a little play, so it doesn't hold it open when in idle position.

EZee

Thanks for the suggestion. I took a look at the cable and sleeve last night and it's secure. Guess I need to keep investigating.

covenant

Im having the exact same issue. Does your voltage go up and down with rpms? if so exactly the same thing is happening to me. same car too 86 na.

zcrazy13

having the same issue on my '86 na car... idle is inconsistent and voltage jumps everywhere while it's idling. My guess is that the voltage fluctuations are being caused by my battery as it is rather old, but as far as the inconsistent idle speed I'm not sure, my idle will dip to 400-500 rpm then shut down, if I put the lights on the idle obviously holds a little higher and the voltage doesn't bob around as much, hopefully someone figures out what it is causing these 86 NA's to idle weird

soysauce300zx

I too have a 1986 300zx and it to idles weird. It idle fine one minute and drop to 500 rpm or so and stumble. We need to get together and figure this issue out. Im changing my idle control valve to see if this will solve it. I will let you know.

zdadgeezer

Erratic voltage etc..Sounds like a bad ground. Make sure all your ground point and electrical connections are not corroded/ oxidized. Can't hurt. Sometimes it is that simple. Heres hoping. I had some fluctuations in idle on my '86 NA. cleaned up terminals, replaced some vacuum hoses(fuel reg and some other short runs that were heat hardened and just didn't feel good) at this point it appears to be holding steady @1000 very steady. Let us know what you find.

ken99

I would double check the throttle position sensor adjustment. I found this discussion that more or less described the symptoms you have when rolling to a stop.

z31.com | Repairs | Throttle Position Sensor

I think the surging idle related to electrical demand is an unrelated problem.

Treacy

You guys don't know how long I've been searching around for people who have the same exact idle problem (word for word) as my n/a 86, 300zx. I don't feel alone in the world of Zs now.

So is there a general consensus as to what causes this idle problem? Most of my vacuum hoses are in pretty bad shape (still hanging on), but bad. I do have that loose cable sleeve that donr1494 mentioned. My PCV works, my EGR seems to work, new air regulator, new plugs and wires, rotor and cap are new, throttle body is clean, throttle cables seem to have to right tension, MAF is clean and works, new cone filter, timing set correctly at 20, and idle speed is set to 7. Everything in the fuel delivery system is new except for the fuel pump.

Any and all your help would be greatly appreciated in helping get my idle speed fixed. I'm just an amateur mechanic trying to get his first car to work.

rogerz

take all the idle junk off the left side of the plenum and blank the hole. get rid of the vacuum crap on the left fender well. run the fpr hose direct to the plenum. get rid of any unused hoses and plug off the stubs. you can also reroute the hoses to the carbon canister under the air filter and back to where they go. that gets rid of the ugly 3 or 4 steel pipes running across the front. cleans things up and it will idle just fine with no fluctuation altho probably a little high. mine runs at 1000.

Treacy

So standing infront of my z, the left side being the one with the egr, pcv, and air regulator? Also you are saying remove these parts I've just listed? As for the rest of your advice, it would be nice to clean up the other vacuum hoses and get rid of the metal vaccum hoses on top of the valve cover.

Also my car is hard to start when its cold (only in the morning) and by replacing the air regulator I was hoping to fix that so I'm a little hiesitent to remove the air regulator if it will fix my problem. I will find out this morning because I put the new air regulator on yesterday.

I get working on your suggestions though. Thanks for the help rogerz!

Treacy

Just checked my vacuum and is stays between 18-22 in Hg. It fluctuates between these two, but mostly stays on 20 in Hg. So my vacuum seems ok. Still set on replacing the vac lines as you suggested.

z31Nightshift

Hey guys yeah same problem with my 86 n/a I was just looking up the vacuumed lines and I found some but it said they were for turbo are the lines the same or should I specifically buy some for n/a?

rogerz

yeah everything on the driver side of the plenum can go. these gizmos might have been fine when everything was new and shiny but now they just make idle problems. while you are at it put new connectors on the FI electric wires (get from Volvo in junk yard are really nice if you can find them). reason your vac fluctuates is cause of those gizmos. It should be a nice steady number (mine is 22 "Hg). anything on the fender well with an unused hose can be junked. Only thing to keep is the boost sensor. run a new hose to it. Couple spuds on the intake rubber piece can be filled with black RTV to plug off. Bingo the three pipe unit is scrap once you reroute carbon canister. do the vac lines for the climate control while at it they usually shot by now

Nightshift vac tubing is vacuum tubing. buy 20 30 feet in bulk pretty cheap you will eventually use it up unless you only keep the car another 6 months.

rogerz

some more unsolicited advice gleaned from doing three turbo 31's. all bought for under 1500 bucks and now running like a scalded ape. Don't forget your timing belt it snaps dead engine. Do the timing belt (unless you have good evidence that is was done within the last 80-90K miles). doing the other stuff above is easier then. figure on being out of action for maybe five six days depending how much time per day you can devote to the project.

Get your battery load tested. Be sure you have clean, tight corrosion free terminals on both ends of your battery cables. Be sure the ground (negative) cable goes to a bolt into the frame before going to the starter. grounding through the starter is not a reliable connection. Z's don't like low voltage. causes the electronics to act funny. it is possible to have enough amps to crank but not enough voltage to run the electronics. If you have one size fit all cheapo clamp on terminals they are a problem waiting to happen.

Clean the connectors for the maf or afm, ecu and tps. Deoxit by CAIG is probably the best connector cleaner on the market. spray with CorrosionX after cleaning and before putting together this will help prevent any further corrosion.

Replace outer tie rod ends, and ball joints. replace the bushings with poly (don't forget to lube them as directed unless you like squeaky things). New shocks. all those things will make you think you are driving a different car. doing them piece meal is a waste you won't see a great improvement until you do the complete job. Rear bushings nice too but more work and you won't notice as great an improvement. Rear shocks also because if the fronts are gone so are the rears. if car squats when you jump on the gas the rears are gone. If you have the electro adjustable shocks they are DEFINITELY GONE.

If you are doing a turbo car shocks (electro adjust I think may be only on the turbos) then you need the adapter plates to fit modern shocks to the car. Easiest way is find an n/a at the junkyard and take the mounting plates. They may be available thru NAPA (listed) but I had the n/a plates.

z31Nightshift

I just fixed my idle all I did was take out the air filter and the mass air flow sensor and replaced the filter and bought some m.a.f. Sensor cleaner and put it all back together. It was a really easy fix and cheep 7.99 dollar filter and 7.99 dollar cleaner. @u@

Flyingltd

would it be possible to get a write up or a better explaination about what can be done away with