Does not Idle or take load
 

My N/A 280ZX does not want to idle when its warmed up. Upon start up it seems fine and the motor idles smoothly. As soon as the motor warms up, the RPM drops to about 400, the motor surges and dies. The motor however revs freely without load. If I drive the car, its got no power over 3000 rpm. The funny thing is that when I put the inside fan (with the A/C off) on, the motor will idle at 800 rpm, but still not smoothly. Switch the fan off and the idle speed drop to 400rpm and dies.

The problem started when I drove the car home after purchasing it. The first 300 miles it went like a rocket, then it lost power and I battled home the last 60 miles to find it also does not want to idle.

I've replaced the following; fuel filter, air filter, spark plugs and checked the ignition timing, but the problem persists. :(

Look at the throttle position switch. It is the black box on the side of the throttle body. Maybe that plug came loose or got wet or something. Make sure all your intake hoses are connected properly around the throttle and air flow meter. ...no cracks in rubber.

I'd also check connections on the air flow meter for corrosion or broken wires and check your head temp sensor to see if it's reading correctly.

Man, that sucks. When I got my car, I test drove it and it was perfect. I bought it and suddenly it would sputter when I tried to go over 50. I drove it 65 miles like that, when I accidently bumped the plug-in that connected to the ECU, and it took off. So now I have it wired so the plug-in is held to one side, and it is perfect. Maybe your problem will be a little thing like that which will be easy to fix

I feel you on that one. When I bought my car I test drove it and it started right up, no problem. Drove it a few mile, ran GREAT. I got an 2 hours down the road made a stop, and it wouldn't start right away. Then it started after a couple tries. I didn't think anything of it, thought maybe it just needed a tune up. Then I got home parked it, and the damn thing didn't start again for two days. After a couple weeks of that crap, I finally narrowed it down to the IM which fixed the first of many problems with my car. Since I replaced all the connectors in the engine compartment I haven't had any problems with my car though. I got sick of trouble shooting problems that just ended up being bad wiring, so I just replaced it all.

And as far as the problem above, I definitely check out the head temp sensor and your TVV's. Couldn't hurt to check the TPS, but since it sounds like your problem is temperature related, I'd check those too.

Denzil,
That sucks man, although I had the exact same thing happen to me a day or two after I started to drive the Z regularly. I fixed mine, hopefuly you can too.

try this...
(In my 81 this is how it is) stand on the driver's side front fender in front of the duct hose connecting the AFM to the throttle chamber.To the immediate right of the throttle chamber housing there is a "T" plumbing connector with a hose coming from the bottom into it and later exiting towards the firewall. If you look through the open hole at the top of the "T" connector you will see a screw, the air regulator screw.

With your engine running (it will be assisted by a friend I take it) and warmed up, adjust the screw back or forth a tiny bit at a time. Have your freind monitor the rpms. I believe the normal operating idle is 700rpm in neutral (not under load) with the a/c off, maybe someone can confirm that.

That I hope will alleviate your erratic idle issue. The only drawback is that with the a/c on you rpm will be higher then 1000, sucks for gas milage.

If that does not help then check and eliminate as follows...
-Idle adjustment screw locatred below throttle valve switch housing in my car anyway, a biiawtch to work at with the rust and all.
-Throttle valve switch (may be opened insufficiently at idle) if malfunctioning will need cleaning of all contact points inside or replacement of the part.
-intake air duct (AFM to throttle chamber etc) for leaks, wear and tear.
-Seized injector (listen for clicking sound)
-irregular fuel pressure (check fuel pump for good wire connections and corrosion etc)

Hope this helps.
Ali

Thanks for the interest guys, I think I found the problem, but I'm not to sure how I'm going to fix it yet. Incidently I'm from South Africa, we don't have emission control over here, and leaded fuel is still available, my car does not have a EGR, TVV, Cat or Cyl head temp sensor. I used the fact that the car idles fairly normal if the cabin fan is turned on as my main clue/lead.

Below the inspection light, there is a small vacuum cylinder, with 3 vacuum hoses and 4 wires connected to 2 electro/vacuum switches. This operates the air ducts/vents inside the car. This is the only place where vacuum and electrics get together, where the inside fan can have an influence. Two of the pipes come from the manifold, one goes straight on and the other is connected to a small diaphram that forms part of the "idle bypass" pluming. I plugged these 2 pipes, the problem remained, but this time the inside fan did not have any affect. I then connected these two pipes with each other thereby cutting out the vacuum cylinder. Bingo, the car was back to normal, and the inside had no affect. The vacuum from the one connection opens the diaphram on the "idle bypass". I now need to sort out the vacuum switches, as I want the A/C to work (remember I'm living in Africa).

Why did the car run normally for the first 300 miles? This is what I think. I bought the car in Jo'burg, 6000 ft above sea level, I then drove the car down to the Zululand coast where I live. The problem started when I came down the escarpment. The elecro/vacuum switches causes an air leak, but due to the thin air in Jo'burg the car was running fine, as soon as I got to sea level it was obviously running too lean. For the first 300 miles the car was very light on fuel, I was cruising at between 90 and 100 mph and achieved 27.5 miles to the gallon. This might support my, running lean, theory. What do you guys think?

I think you should be a detective!!!

Nice work.

Rod.

Ali, yes this did help. Once I got the motor running smoothly I started on getting the A/C working. :rolleyes: I honed in on the 2 electro/vacuum switches on the little vacuum cylinder. The blue wire has current when you switch the fan on, thereby allowing the vacuum to open the vents in the car. The yellow wire has current when you switch the A/C on, thereby opening the diaphragm on the "idle bypass" plumbing, allowing the motor to idle faster to pul the A/C. The pipes were swaped around and the idle speed was to slow. Swapped the pipes, cranked up the idle and the motor is purring like a kitten at 750 rpm, A/C on or off.

To recap, the yellow switch, gets the yellow wire and the pipe with the yellow stripe, connected to the diaphragm on the idle bypass. Took me the whole weekend to sort out. :D

Thanks for the help. ;)

Good to hear that it worked out for you...and thanks for providing insight into a potential problem someone here could face at sometime