1985 Nissan 720 idles rough in D, fine in neutral

[SCBlake1988]

Hello,

I recently bought a 1985 Nissan 720, and am having trouble. The car starts fine every time and idles well in Park. After driving and the car is warm, the trouble begins. When I slow down at a stop light, it idles rough. However, if I shift to neutral it idles fine.

I noticed that when it is idling rough it goes through a cycle. It will idle for a few seconds OK, then have a rough jolt and there is a clicking sound, then starts over again. Its not completely constant, but that is the general pattern to it. Idle Idle Idle, click click click, idle idle idle. When looking under the engine I couldn't pin point the exact location, however I think it is coming from the passenger side.

The car runs fine in motion, and accelerates fine too. It just idles rough once warm and engaged in Drive, Reverse, etc.

Any ideas?

Blake

[MaximA32]

It sounds like you're having some spark plug wire arcing issues. Do you have a spot you can take it to that is dark? That way you can see if any of the plug wires aare arcing. It could also be a vacuum leak but I would guess that's not the case.

[SCBlake1988]

Yes, I have a garage that I could test it in. Am I just looking for sparks?

Any other ideas while I am under the hood this weekend?

[MaximA32]

Yes, you're just looking for white/blue spark arcing from wire to wire. I would also get some carb cleaner spray and spray the vacuum lines and see if that changes the idle at all. If the idle changes, that means you have a vacuum leak in the vicinity of where you just sprayed.

[jrchester1]

Hi, Blake!

What color is your Nissan 720 by chance? I am looking for a white one and wanted to know your thoughts.

Thanks!

-J

[PEZi]

I was going to go with vac leak. If you don't get it fixed via spark, check all vac lines related to the trans.