mr_g

i have a problem with my car idling....sometimes when my car has been running for awhile my rpm jumps up 200-300 up and down....like if it idle's at 700-800 it'll jump up to 1000-1100 and go down to 700-800 back up to 1000-1100 over and over....also sometimes when im crusing steady or when i go over 55mph+ i can feel the car jerk stop and jerk stop over and over....it only jerks a little but i can feel it....like the rpm's going up and down i dont know what the problem is so if any of u guys out there might know what my problem is please let me know....i have a 1985 nissan sentra 2 door hatchback 1.6L (carburetor)....

bob89sentra

Fluctuating idle can mean a few different things...
First check your spark plugs and wires along with cap and rotor.
Could be plugged fuel filter
Could be vacuume leak
Could be Burnt valves.
The fuel filter is an easy and inexpensive change out. If you have a vacuume gauge you can hook it to the intake vacuume, and see what it is doing. There is a whole section in the chiltons repair manual that helps diagnose what the readings you get mean. Also If you have a compression tester you can check your compression, using the wet/dry test. First check the compression on each cylander and write it down. If it is between 80 and 140 PSI and within 10-15 PSI of eachother they are probbaly ok, if they are low or one differs from the rest squirt a little oil in each cylander before you recheck it. If the compression numbers go up signifficantly, you have worn piston rings. If they stay the same you have burnt/ leaking valves.
Bob

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89 Sentra owner 9 years 205,000 miles and counting!

mr_g

i got new spark plugs, cap, rotor, pcv valve, and fuel filter....im thinking maybe i have a vaccum leak somewhere....