First off, I'd like to thank anyone that is willing to read this and possibly help with my problem. I've been tackling this problem for a few weeks and I'm not seeing much improvement. I would like to add now that I bought the car about 2 months ago, and that the car mostly sat outside in the sun all day, not driving. It is a 1983 280zx 2+2 Non-Turbo


The Faults:
1. Overheating. After driving around for about 20minutes, the car will warm up like it should. The problem is, I cannot keep it at operating temperature. It will go past and probably all the way to the end of the gauge +, if I never shut off my car immediately. I have noticed that having the engine around 1.5k RPM+ drops the temperature, even if I'm stopped.

2. Stalling. After it warms up and is at operating temperature, after idling at a light for about 2 minutes, the RPMS will start flunctuating. A few seconds later, it will try to shut off on me. It will remain running rough unless I boost up the RPMS, which then it will run fine.

3. Rough Idle. I have my idle set at 900 RPMs. If I try and put it at factory around 750, the engine will start shaking, and the RPMs will fluctuate.

The Car RPMs always fluctuate in Nuetral/Park, but not if I have the throttle open.

What I have checked/Replaced:
Cooling System=
New 160 F thermostat
New Radiator Cap
New Hoses (most of them were cracking when I bought it a few months ago)
New Gaskets
Checked Water Pump
Checked Cooling Fan
Flushed Radiator/Block

Ignition System:
New Rotor
New Dist. Cap
New Ignition Coil
New Plugs
New plug wires
Checked Spark (Also seemed consistent when testing)

Air system:
Checked All vacuum hoses in the engine bay, replaced damaged ones.
Checked AFM, has a small deadspot but otherwise alright
Checked TPS

Fuel System:
Nothing really yet.

I also have no knowledge on bringing back a car from sitting for a long long time, so if you have any useful tips of what I should do / check that would be great. I am going to replace the fuel filter this week since it should be replaced anyways. Thanks for reading!

 

Welcome to zdriver! I'm pretty new, but one of the older members will probably sweep in here soon with more thorough advice.

Engine Temp: Have you checked the Cylinder Head Temperature Sensor? It is located right below the #5 and #6 spark plugs. The one on my car had gone bad and was causing some idling problems. Also, there is a coolant temperature sensor. If your gauge is accurate, though, it might not be the problem.

Unever idle - let's start with the cheap stuff and move up! Have you drained out any old fuel? Have you changed out the rubber fuel line hoses? Made sure that the fuel filter isn't all gunked up? What about the gas tank? could it be rusted on the inside? (mine looked immaculate on the outside, but was incredibly rusted on the inside, even though it had sat in the california sun for most of its life). I would suggest disconnecting the line at the intake for the fuel filter and the fuel pump and and blowing some compressed air through the lines to clear out any blockages. Uneven idle could also be a bad air regulator. My guess (because of the shaking at 750) is that it could be a bad fuel injector, or bad electrical connection to the fuel connector (due to the fact you said you've already checked spark). This could cause you to miss a cylinder and for the car to shake. Just a guess, though.

Don't know if you have it, but the factory service manual can be a great tool for diagnosing. you can download it here: http://www.xenons130.com/reference.html

Searching the forums is also a great tool. Be sure to do an advanced searched, and limit results to the 280zx forums, though.

Best of luck on the Z!

 

My thoughts would be head gasket...

Is your coolant level dropping at all? When the car is idling, take off the radiator cap; are you getting any bubbles coming up?

 

You might want to do a block test and check timing . If the head is blown , it will run hot and/or rough .

 

one quick test for a vacuum leak is to pull the oil filler cap while the car is idling. If it runs the same you have a vacuum leak. If it runs worse than likely not. put a vacuum gage on the system and see what your vacuum is. check the fuel pressure. did you check the ignition timing with a timing light. is the plastic fan shroud still in place this helps direct air flow thru the radiator. borrow an infrared heat gun and see what the temp on the radiator actually is. stock gages are notoriously unreliable. often the sensor as suggested above.

 

UPDATED

My coolant level never drops, and I am sure that it's holding pressure really well.
UPDATE: Took off cap, no bubbles.

I do not have a pressure gauge currently. How do you check the fuel pressure? I do not see any service ports. I did check timing, but it was odd because there's a factory notch and then someone used a paint marker on it. The notch seemed way off, so I went off the paint marker and set it at 8 degrees BTDC while the car was hot. The shroud is still in place. I have used a infared gun, and my temps down the radiator were around the 110 area, and was colder as it was down. I found it odd that the hose that enters the water pump area had a temp of 140.
UPDATE: Idle got rougher when oil cap was odd

I have tested the Cylinder head temp sensor and saw that it was in a ballpark area where it should be. I have already downloaded the service manual from there and have been using it. Very helpful stuff. I have not replaced anything with the fuel system yet, nor tested it besides the electrical connectors. I did notice that 2 of them had weak connections, but after what seemed like fixing them the idle still isn't great. It is very noticeably different when one is disconnect though. I have a whole new set of Fuel Injectors, but have not put them on yet because the fuel rail seems like a giant pain, so I am waiting till I have enough free time. How can I check the inside of my Fuel tank?
UPDATE: Tested ohms of the cylinder head temp sensor, was at 333k Ohms after about a 5 mile drive.

UPDATE:
I tried to pull off the cylinder head temp sensor, but the nut portion broke right off! I don't know how I can remove the sensor now to properly test it, if anyone has any ideas, that would be great!

 

Hmmm.... 750 seems really low for idle. I have mine set at 1k.

Ok, bear with me here I don't have a picture of this so I'm going to explain it......

Follow the air intake from the AFM back towards the block. When you get up to the intake section, you should see a flathead screw sunken down about a 1/2 inch. Turn that thing about 3 turns to the left and open it up while it's running. Your idle should even out. It won't run faster or slower...much... but that should help.

Also, check to see if your cold start valve isn't stuck open. There is a plug you can disconnect to try and see before removing it. It's like a 7th fuel injector, but it should only open when the car is cold. If it stays open, your car will act like it's flooding.... rough idle.

 

Cooling System=
New 160 F thermostat
New Radiator Cap
New Hoses (most of them were cracking when I bought it a few months ago)
New Gaskets
Checked Water Pump
Checked Cooling Fan
Flushed Radiator/Block

You forgot to replace the radiator it's 30+ years old!!

Also check your fuel prusser!!



Download the Factory Service Manual and do some reading.

 

There are several ways to go about this. The first is to check where you put in gas. If that part is rusted, then the tank could be rusted as well. I got an borescope from Harbor freight for cheap and fed the camera down the tank input hose to look inside the tank. Even though my car had been sitting in California, water had been leaking past the gas cap and into the tank, causing massive rust.

If you don't have a borescope, you can disconnect the input hose from the gas tank. You will have to take off the plastic cover on the passenger side rear wheel, but it is pretty easy to get on and off without dropping the entire tank. The screws for the plastic cover are 10mm (I think). The hose there is pretty thick, and you can see into the gas tank pretty well if you have a flashlight.

The most time-intensive option is to try to drop the tank. You have to start in the cargo area and remove the foam padding and carpet. You will find a circular metal plate, remove that you and will have access to the fuel tank gauge unit. Again, several more screws (these ones can have a tendency to snap, so be careful!). There will also be 3 hoses and an electrical connector you will have to disconnect. At this point, you can get under the car (assuming you have it jacked up and on stands) and drop the tank. The bolts holding the straps for the tank are 13mm (I think) and I needed a deep socket and an extender to get them off with my socket wrench. Like I said, this is the most time intensive, taking about 30 minutes if you are familiar with it, or 2 hours if you are me.

Honestly, I would try checking the fuel line before anything else. Best of luck with the Z!

 

If you are just back there and want to check for rust in the tank, why not just pull the sending unit cover off (remove all those screws) and take a peek inside. Saves the time of dropping the tank if you don't need to. Just few minutes and you have a clear view of the inside of the tank... the only thing that is a pain is if you need to replace that big o-ring and that's usually because you have to wait for the dealer to get it...

Good to check those hoses from the tank to the pump and the return as well...

 

Have you checked the timing yet? Have you verified that your gauge is working properly? I swapped in an analog gauge and though the car was overheating when it was simply a faulty gauge....

 

to check fuel pressure you have to make a rig to put in between the filter and the fuel ring since i have never discerned a viable way to post a pic on this forum you need a pressure gAGE (use one that says oil pressure for about 5 bucks from any parts stores. go to a hardware store and get fittings needed to tee off between the filter and the fuel ring. OR go to harbor freight and buy their 40 dollar model. forget all the exotic stuff and be sure the basics are there.

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, 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.

 

On the overheating aspect you might just need to replace the fan clutch if its bad it will cause ur car to overheat at anything but an idle hope that helps

 

Roger,

I have the exact same problem with my 1972 240z carrying 2 Hitachi SU carbs recently remanufactured my Ztherapy, Schneider 274F cam with .175 lashpads, new rocker arms and springs. Also Pertronix 1761 ignitor with 3.0 ohms Coil. new ngk bp6es spark plugs gapped at .031, new cap and distributor rotor.

Start the car, warm it up for a while then take it out of the garage and whenever stuck in 2 mins traffic lights, Idle becomes rough, RPM lowers and rises. Suddenly it lowers to 500 RPM and rises and after many traffic lights, the car shuts down (stalls). Its really uncomfortable to drive this way. Car has gone through 5 mechanics. None of them have been able to solve this issue.