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Hello everyone, I am experiencing an unusual problem with my 1980 NA 280ZX. Sometimes when I'm driving, after the car heats up it will idle high ~2500 rpm then sometimes it goes back down to normal later. It happens about 80% of the times I drive it, and doesn't seem to be running rich, or lean, and it's fine anytime I'm in gear. I tried checking for vacuum leaks with water (no luck) and would prefer to avoid checking a hot engine with starter fluid or propane. I also tried wiggling all the vaccum lines I saw, with no luck. I checked to make sure the throttle is returning all the way, and checked the cold start injector. I bought the car about a year ago but this didn't start happening until a month or two ago. Has anyone had a similar problem or have any other things I should check for?

Also I appologize if someone else has posted about this before, I tried to look through the other posts and didn't see anything quite like it, but I could've missed one.

Thanks!
 

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The best way to check for vacuum leaks is with a hand pump and pack of cigarettes. The method for this is all over these forums.

That said - your problem is most likely the "matchbox" on your distributor. These go bad and create these issues so you will need to replace it. For reference, this the black box (it says e12-80 in green):
 

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1983 280ZX Turbo
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The "matchbox" is the ignition module on the side of the distributor.

I had one go bad on an 82 ZX, and in my case when the engine got hot the tach would drop to zero and ignition would cut off completely. After a few minutes it would start again.

I devised a test. I carried a thermos of ice water with me. When the engine cut off, I pulled over, popped the hood and doused the module with ice water to cool it off. Got back in, the car started, and I knew it was the ignition module. It's an easy test to try.
 

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The "matchbox" is the ignition module on the side of the distributor.

I had one go bad on an 82 ZX, and in my case when the engine got hot the tach would drop to zero and ignition would cut off completely. After a few minutes it would start again.

I devised a test. I carried a thermos of ice water with me. When the engine cut off, I pulled over, popped the hood and doused the module with ice water to cool it off. Got back in, the car started, and I knew it was the ignition module. It's an easy test to try.
Dumping ice water on an electrical component didn't short it out?
 

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1983 280ZX Turbo
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Dumping ice water on an electrical component didn't short it out?
Think it over. It's outside the distributor, and designed to be driven through rain and inclement weather. Everything inside that engine compartment can get wet. And it's a sealed box with one wire coming out.

Not a problem, and you're not going to pour a gallon of water over it, just a few ounces to cool it off. Don't worry about it.
 

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Think it over. It's outside the distributor, and designed to be driven through rain and inclement weather. Everything inside that engine compartment can get wet. And it's a sealed box with one wire coming out.

Not a problem, and you're not going to pour a gallon of water over it, just a few ounces to cool it off. Don't worry about it.
gotcha - fair enough
 
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