RPMs going between 1 and half while on drive not on park?

HUSSEINALIM

MEMBER
2008 NISSAN SUNNY
1.6L
4 CYL
2WD
AUTOMATIC
800,000 MILES

I was driving and the car had the battery light on. After a while the A/C went into giving only air but without being cooled, the fuel pedal didn't work on drive at all or just giving a little push to the car but not while on park or neutral. I drove to a mechanic, but it stopped on an uphill road for which I had to transfer it.
They said they'd fixed the dynamo and that was the problem.
Took the car and after a while I experienced an issue where the rpm goes very low (below one or even below half) while speeding down on a bump or in traffic to the point that the car even shut down and I had to restart it and use brake and fuel pedal together to prevent this in traffic or at very low speed.
Now the problem is still but to be accurate when on drive and not moving the rpm goes fluctuating between 1 and half and even shuts down frequently and the AC flow goes though from very good to low. Note that I had changed the camshaft sensor recently and upper sensor so. The battery is 2 years old. Fuel pump changed recently. Spark plugs changed and are inspected now and in good condition. Coils inspected for tear and no tears present.
Thank you.

1 Reply

AL514

MECHANIC
4,793 POSTS

Hello, not too sure what they replaced meaning "dynamo", but I'm sure the check engine light has been on through all this, with the battery light on as well, did you have the charging system checked fully to begin with? And have the engine computer (ECM) scanned for diagnostic trouble codes? If so, what codes were set? The US model comparable to this is the Nissan Sentra, and it uses a Mass Air Flow sensor to read the amount of incoming air into the intake manifold, and the idle is controlled by an electronic throttle body, so if the vehicle wont idle on its own, the ECM is having trouble keeping the throttle plates open enough for any number of reasons. But you might want to have a better shop look at the vehicle, it doesn't sound like they were being too honest about their diagnosis. This isn't going to be an isolated issue like a spark plug or ignition coil, it's something affecting the entire engine management, which should be setting a trouble code, especially on a 2008. The AC is going to be affected because the air conditioning is a major load on the engine and it can't handle that right now, so disregard that until you get the idle issue figured out.
Here are a couple of guides, but I would start with getting the entire vehicle scanned for trouble codes, write them all down, and we will be able to give you some better direction. Tell the place, wherever you take it, you need a full system scan done. They should be able to print you out a health report for the vehicle. If the battery light is still on, low system voltage will cause everything in the vehicle to malfunction.

https://www.2carpros.com/articles/engine-surges

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge