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Discussion Starter #1
Hello all!

I've been having a problem with my car idling rough 500-600-700-800 rpms back and forth. Also when I rev it it sticks at 1200 rpm or so. I have already changed the egr solinoid valve, air regulator, spark plugs, spark plug wires, and most air hoses.

I want to check the cylinder head temp sensor (chts) without replacing it. If I unhook the harness, which I believe I see next to the #1 spark plug, and hook it up to a new harness with a new chts attached will this do any damage? Maybe I don't need to let the engine get too hot?

I also saw where someone on here recommended unhooking the mass air flow sensor and then cranking the car. I don't know if they were talking about removing the unit itself or just unhooking the electrical connector. I unhooked the electrical connector and the car would not crank.

Thanks for the replies.
 

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My first recommendation would be to check your codes if you haven't already. That should tell you right off the bat what the problem is. Let us know what it says and then we can help better. Does it only do this when the engine is cold or all the time? If its all the time, then it probably isn't the CHTS. Give us these details and we can help more.
 

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Discussion Starter #4
Thanks for the replies.

85 zx non-turbo, manual trans.

Sorry, yes, I ran the codes the other day and everything was normal.

It does it when it is cold all the time, and when it is hot some of the time like when I'm sitting at a red light. When I take off in the morning (cold) it bucks. When hot and moving no problem except it uses about 25 to 50% more gas than it used to.

Besides what I indicated in my previous post about parts changes (listed below),

"I have already changed the egr solinoid valve, air regulator, spark plugs, spark plug wires, and most air hoses."

the fuel filter is new, and the distributor cap and rotor are practically new.

Also, the car sat for 2 years but I have burned out all the old gas--2 tanks since then. Black smoke is coming out the tail pipe sometimes (most of time). Although, I can only tell this when idling. The spark plugs were covered in black carbon.

Thanks again!
 

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jacrum -

I also have an 85 non-turbo and I was experiencing the exact same problems that you were describing. After much research and help from Slicktop at z31.com I found the solution to the problem and my z31 has been running smoothly, regardless of temperate, since.

Check out this link which I am just now posting on my website:

http://www.zheritage.com/index.php?page=leansurge

I don't know if this is your problem but what you are describing is exactly what I was experiencing for 5 years prior to this fix.

If you ran the codes and they didn't flag the CHTS then it is almost certainly not your problem.

Good luck!



Post Edited (Oct 21, 8:35am)
 

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"Also, the car sat for 2 years but I have burned out all the old gas--2 tanks since then. Black smoke is coming out the tail pipe sometimes (most of time). Although, I can only tell this when idling. The spark plugs were covered in black carbon."

Ok, my recommendation: get a timing light and verify your timing. sounds like if your plugs were covered with black deposits, you're getting detonation or preignition and your timing is probably off.
 

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In addition check the o2 sensor if you are getting that bad of gas mileage. If the car is still doing these things when warm, there is something more than the CHTS wrong. Like phxz31 said, check timing and i would check the o2.
 

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Yeah it probably would have thrown a code, but I'm just recommending he check other things because it could be the CHTS causing the cold start issues, but something else is obviously wrong if it still does it when warm. This problem is a serious hassle to diagnose sometimes.
 

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Discussion Starter #11
Thanks for the replies!

I ran the codes again with a different computer and it gave no error codes. I changed in three other computers and two them did pretty much the same as the first one I did codes on--first post above. The other one acted like it wanted to choke off. This was somewhat different than the other three (original + other two I swapped in).

I did this from first post:

"I want to check the cylinder head temp sensor (chts) without replacing it. If I unhook the harness, which I believe I see next to the #1 spark plug, and hook it up to a new harness with a new chts attached will this do any damage? Maybe I don't need to let the engine get too hot?"

and I got the same bad results as before--no change. The engine was warm but the cylinder head temp sensor was outside temp (90 degrees). The car's temp gauge was half way up the dial. I may do it again in the morning when engine is cold.

One thing I noticed is that if I take off the hose that goes from the engine to eventually the fuel pressure regulator at the engine point, this will let in more air to the engine and it will run better. It will almost run smoothly but not quite, and some black smoke still comes out the tail pipe.

I don't have any experience with a timing light. What is the difficulty in using it?

Thanks!
 
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