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Engine RPM erratic fluctuation - Nissan 6

I have an 86 Pickup with the 6 cylinder engine. I recently received it from a relative so I have no real driving history as to the problem. It has 109K. If held (in neutral) at mid-speed the RPM's will dip quickly and than return to the mid-speed. It will keep doing this. It seems to do it more so once the engine is warmed up. If I'm driving I'll notice the hesitation but if I give it gas it will smooth out and take off. It's not missing and does not lack power. I've changed the fuel filter, air filter, PCV, ignition wires and plugs. I'm also in the process of replacing the induction valve filter assembly that is pretty much rotted away. Any ideas? thanks

Reply to
mister880
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Hi.

I had a Subaru that did that: it would especially do it at idle speeds: Erratic changes that would be impossible for the engine to have made. In my case, I replaced the distributor: It had slop in its bearing, causing it to not run properly by the crank angle sensor. It could also be the crank angle sensor - these signals are very tiny and easily get lost going to the ecm.

Hope you nail it soon. Remco

Reply to
remcow

Reply to
John Smith

Sounds to a similar problem I had when I had the same truck (86.5 Hardbody w/VG30 engine). Had it at the dealer for a week. They found the harness connections at the computer (under the passenger seat) needed a good cleaning. Once they cleaned it up, problem seemed to have gone away. Mind you, I only kept the truck for another 6 months.

*FYI: Problem I had while driving at freeway speed (55-60 mph, rpm's on tach would be stable at around 2000 rpm, the drop to low 100's or zero, bouncing up & down, then return to normal. Also, only slight hesitation, then everything ok. Kept happening every time while driving.

Reply to
: )

Thanks to all those who tried to help me solve the problem. I checked out your suggestions but the problem persisted. I finally took it to the dealer who correctly solved the problem; it was the oxygen sensor. Thanks again for your suggestions and help. Mister 880

Reply to
mister880

For anyone who read my post of 12/30 please disregard. I jumped the gun assuming the dealer had the problem solved. I picked the vehicle up from the dealer today and it's even worse. It now fluctuates even when it's cold. Previously it did it only after the truck warmed-up. So much for the new oxygen sensor and the almost $200 charge. I'll post the resolution if I ever find one. It's back to the dealer for now.

Reply to
mister880

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