Will not rev for 30/50 seconds after starting, then ok although a little sluggish
The "won't rev" part sounds like a preventative so you won't destroy the engine from cold start-up. The sluggish part sounds like bad fuel or spark plugs. Where do you buy your fuel and what octane is it? and have you Changed your plugs?
SOURCE: when cold, it idles rough, revs high then low! After warmed up it runs fine
if it runs high when you first start it then mellows out,, theirs no problem , all of our chevys do that.... but if its sputtering or you hear a quiet popping noise check spark plugs
SOURCE: starting problems golf mk4 1.6 petrol
There is a part between the air intake manifold and the air box on your engine, it's usually black on a golf, will look like a 15cm tube around 80-90mm in diameter with a plugged wire leading into it, this is your MAF sensor or MASS AIR FLOW sensor and if dirty / faulty can cause an incorrect temp reading from the air intake and cause rough engine starting, this is a very common problem on mk4 golfs... the part is apparently cleanable, with isoprop alcohol, or I assume white spirit. the actual sensor needs to be removed from its housing for cleaning, and as always treat carefully... the part replacement, depending on where you go can be around $50 - $100 used or even new.... part number off the existing one on your car, try ebay as you can do well for price :) could be fouled spark plugs from rich fuel mix on bad airtemp sensor, could be a million things but the MAF sensor is one of the golden oldies I'd be checking first :) Goodluck, Chas
SOURCE: running rough, no power misfiring
i had that problem once. when i got under half a tank of gas in the tank. What i did was i dumped one bottle of gas line deicer in the tank and i have never had it agian. you may have some water in the tank. from condasation or i have a stong feeling i got my water from the gas station. i was using the same station all the time. so i tryed another gas station and so far no more rough idleing which was caused by the water i think and i am getting better fuel milage to. i hope this helps.
SOURCE: I am having ongoing problems with the truck miss
Misfire is a common driveability problem that may or may not be easy to diagnose, depending on the cause. A misfiring cylinder in a four-cylinder engine is, pardon the pun, hard to miss. The loss of 25% of the engine's power output is the equivalent of a horse trying to run on three legs. The engine may shake so badly at idle that it causes vibrations that can be felt in the steering wheel and throughout the vehicle. The engine also may be hard to start and may even stall at idle, depending on the accessory load (air conditioning, headlights and electric rear defroster, for example).
When misfire occurs, performance suffers along with fuel economy, emissions and idle quality. And, when a misfiring vehicle is subjected to an emissions test, it will usually fail because of the unusually high levels of hydrocarbons (HC) in the exhaust.
What causes a cylinder to misfire? Basically, it's one of three things: loss of spark; the air/fuel mixture is too far out of balance to ignite; or loss of compression. Loss of spark includes anything that prevents coil voltage from jumping the electrode gap at the end of the spark plug. Causes include worn, fouled or damaged spark plugs, bad spark plug wires or even a cracked distributor cap. A weak coil or excessive rotor gas inside a distributor would affect all cylinders, not just a single cylinder.
"Lean misfire" can occur when the air/fuel mixture is too lean (not enough gasoline in the mixture) to burn. This can be caused by a dirty, clogged or inoperative fuel injector; air leaks; or low fuel pressure because of a weak pump, restricted filter or leaky pressure regulator. Low fuel pressure would affect all cylinders rather than an individual cylinder, as would most air leaks. A leaky EGR valve can also have the same effect as an air leak.
Loss of compression means the cylinder loses most of its air/fuel mixture before it can be ignited. The most likely causes here are a leaky (burned) exhaust valve or a blown head gasket. If two adjacent cylinders are misfiring, it's likely the head gasket between them has failed. Also, if an engine is overheating or losing coolant, it's likely the head gasket is the culprit.
Intermittent misfires are the worst kind to diagnose because the misfire comes and goes depending on engine load or operating conditions. They seem to occur for no apparent reason. The engine may only misfire and run rough when cold but then smooth out as it warms up. Or, it may start and idle fine but then misfire or hesitate when it comes under load. Also, it may run fine most of the time but suddenly misfire or cut out for no apparent reason. Intermittent misfires can be a real challenge to diagnose, so let's start with a steady misfire in one cylinder before moving on to intermittent misfires.
Hope this help.
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