My 1984 Nissan K.K. 4X4 with a 720 engine has developed a idle issue. When cold it runs at 2000 RPMs. When it warms up it likes about 1600-1700 RPMs. When warm it cycles RPMs hi to low but never settles down at it normal 1K idle speed. How do I fix this issue. FYI- 350000 miles orignal engine never rebuilt. Carb never touched, honest.

sounds like a vacuum leak... how fast are these cycles???

Cycles fairly quickly. Lately it has, at times, settled down for a while but starts to cycle again. If it is a vaccum leak where do I look?

How the manual tells you to look for Vacuum leaks Grab some tubing and listen to the vacuum lines (like a stethoscope) until you here a leaking noise.

Or goto auto parts store and start replacing vacuum lines one by one until resolved or you replaced them all. If it doesn't fix the problem look into EGR and carb.

Thanks so much, I'll keep you up to date.

also try cleaning the linkage on the carb, if it gets gummed up the choke will stay on. just use a good carb cleaner.

I have repaired a bad tube under the air cleaner and that has solved the problem. Another question...I have developed a issue with my fuel pump. It shuts off when it feels like it. I replaced the pump but that did not fix the problem. I think it could be a solinoid issue. After the engine dies and I sit for about three to five minutes it starts to pump again. Are they prone to act like what I am describing? Dies thens starts again?