mhilldruf1024

So I am new to this forum as well as automotive maintenance so I am just trying to get some advice from more experienced z owners. I have been having an issue where as soon as I start my car it idles low at like 300 and fluctuates to 500 and back down and makes a sputtering noise. If I apply any throttle greyish white smoke will come out the exhaust. Also, the car is '76 but the engine is an '83zx and I am not sure if I need to replace the afm and ecu or if the shop that did the work recalibrated the ecu for the newer engine. The problem existed with both engines. Anyway, I will be performing a vacuum and timing test as soon as I get the chance, I am just weeding things out at the moment. Any knowledge of my issue would be helpful!

NismoPick

Welcome to ZDriver!

A basic check over would be the first thing to do. Make sure you've downloaded the FSM (see link in your Welcome PM).

Check:
-Compression
-Timing
-Fuel pressure
-Read and compare spark plug tips
-Check color of oil and coolant
-Check all sensors

The major difference between the 76 and 83 engines is the cylinder head temp sensor (CHTS) for 80-83 and coolant temp sensor (CTS) for 76-79. The CHTS is located between spark plug 5 and 6 in the cylinder head, while the CTS is located in the thermostat housing. You need one... and doesn't really matter which. But that is a major component for the a/f ratio.

mhilldruf1024

Thanks for the tips! Actually I have replaced the coolant temp sensor as well as the coolant. I have not checked the cylinder head temp sensor because I looked and there is nothing connected to it, and I dont even see any loose connectors near it so could be an issue. As for the other checks, compression is good, fuel pressure was good but I checked behind the fuel filter, not near the injectors. Spark plugs were charcoal black when I replaced them 6 months ago, havent checked again yet. Next on my list is the timing check though. Thanks again for the info, I will take a look at all of those and see if I find anything

NismoPick

Hopefully you mean this, in the thermostat housing? As long as it's connected to the ecu instead of the CHTS, it's fine... otherwise yes, the CHTS needs to be connected.

CHTS and CTS is the same sensor, just different locations:

mhilldruf1024

Ahh ok, i understand now. Yes it is connected to the ecu, guess the cths is just there to plug the hole in the block.

rogerz

no the hole is a dry hole. the CHTS is a two wire device the sensor for the temp gage in the cockpit is a single wire. If you got an 83 engine why in the ten thousand names of god would someone put the chts in the thermostat housing. the moron couldn't figure out how to rewire to it?

Have you checked for vacuum leaks they are the bane of the FI engine.
You didn't really check the fuel pressure if you did what you said. You need to know the pressure between the filter and the fpr. but I don't know your definition of behind the fuel filter most people use inlet and outlet to avoid confusion.

mhilldruf1024

The sensor in the thermostat housing is a coolant temp sensor. And yeah i checked the pressure right behind the filter so i need to check again between that and the fpr. Also i have not checked the vacuum yet, but that could def be an issue.

mhilldruf1024

So I randomly pulled off the plug that is on my throttle body (everything is capped since the EGR stuff has been taken out) and the idle issue jumped up to normal immediately. It still fluctuates 100 rpm, but it's where it's supposed to be around 800 rpm. If I place my thumb where the cap was the issue immediately comes back. Could that indicate something is wrong with my air flow meter right before the throttle body?

NismoPick

Please post a pic so we can see what you mean.

mhilldruf1024

First picture is with the plug on, second with it off. Runs much better with the plug off