1995 Jetta CSL petrol idles irratically. What could cause this? Rev counter also jumps when idling. Replaced fuel pump recently.

Has it been serviced recently? Check the basics for petrol engines. Clean air filter, clean fuel filter, clean oil and oil filter. Is the battery fully charged? Is there fuel in the tank? (Yes, I've done that one). If there is a fuel tap fitted to the bottom of the tank? Is it in the open/run position?
Yours sounds like a fuel supply issue. How old is the bike? Does it idle smoothly when it does run? A good starting place is the fuel pump. Some scooters use a vacuum system for the fuel pump and the rubber diaphragm inside the pump wears out. This doesn't pull the fuel through fast enough and leaks air into the fuel system. This starves the engine of petrol, causing it to stall.
A lot of older bikes also use carburetors which need to have the fuel jets and idle jets cleaned occasionally, especially if there has been poor quality fuel in it at some time. Newer bikes use an injector which can clog up as well but this is less common.

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for unleaded fuel around 6? on idle ,this vehicle has a distributor as such and its possible to adjust this by the 10mm headed bolts on the housing any higher than 8? and the engine will pink .

sounds like throttle body not fitted correctly or needs adjustment of idle sensor or idle speed control

check elec

Your problem sounds as if the thermo sensor....which controls the air fuel ratio when engine is cold....is faulty. It is a common fault on this model.
This is not an expensive part, and takes only a short time to fit.
Good luck
John

sounds like the idle speed sensor,if your rpm's are idling up and down

renault ---dealer only

There is an idle air control valve that controls the idle rpm, which causes the nice smooth idle. When they go bad, it won't idle, jumping from hi rpms to low enough to cause the car to die. The ones that I've replaced were easy to access and replace, usually on the intake manifold area. This will also give you a check engine light. Beyond this, has the engine had a good tune up lately? To check this correctly you should check fuel pressure coming from the pump, check spark coming from distributor. Good luck. Colin

sounds like filter (fuel) is clogged. causing a strange fuel flow.