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85 300zx non-turbo, manual trans.

First I changed out my oxygen sensor and it cured my erratic idle and black smoke coming out my tail pipe. (Thanks for the previous help guys.)

Although, my car still will not idle correctly. It goes to about 1200 or 1300 rpm and mostly stays there (even when at operating temp.). I started the drivability test and did the timing.

(I still haven't changed out the cylinder head temp. sensor.) (I haven't run the codes again yet but there were no error codes when I ran them before fixing the oxygen sensor.)

Here is how the timing went, with question:

It was off by 3 to 5 degrees (25 degrees PTDC). I adjusted it to 20 degrees PTDC. While watching the light after adjusting it (after tightening it down) it would sometimes show the mark about 2 degrees before 20 degrees PTDC and sometimes it would show the mark about 2 degrees after 20 degrees PTDC. Is this normal for the timing light--to sometimes travel to the left or right of the point you have set it on--or should you only see the point you set it on?


Also, I unhooked the idle-up solenoid valve and the rpms went to 800 rpm. It is very hard to turn the little screw to adjust it. How far do you have to turn it to the left or the right to get it to go to 700 rpm? I turned it about 33% to the left and it did nothing. I hooked it back up and the rpms went back to 1200 to 1300 most of the time but never all the way back down to 800 rpm. It would go to 1000 rpm sometimes. I would rev the gas then it changed a little.

Any suggestions? Thanks a million!
 

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I have the same problem. Its the aac valve from what i can gather and its stuck open. I got a used one and it did the same thing so i put a valve in the hose and adjusted it to 700. I never tried a new one but i am happ now
 

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Thanks for the correction phxz31. I just remembered the acronym wrong. It is BTDC. Does the B stand for before? That makes no sense to me as far as the marks go.

The mark it was on before changing it was the mark next to the last mark on the right (while looking at the front of the car). The Factory Service Manual (FSM) showed this as 25 degrees BTDC. I put my car on the mark to the left of the mark it was previously on, which would be 20 degrees BTDC. The FSM said it should be on 20 degrees BTDC +2 or -2 degrees.
 

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"The mark it was on before changing it was the mark next to the last mark on the right (while looking at the front of the car). The Factory Service Manual (FSM) showed this as 25 degrees BTDC. I put my car on the mark to the left of the mark it was previously on, which would be 20 degrees BTDC. The FSM said it should be on 20 degrees BTDC +2 or -2 degrees."

that sounds absolutely right.
 
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