Audi a3 1600 1999 car cuts out when cold after taking foot off the throttle but once warm normally ok but this doent happen all the time. Erratic rev counter when problem about to occur

I do believe you are correct, but here's how the system works. You turn the switch on, the computer is activated, the temperature sending unit, sensor sends a signal to the computer that it's cold so the computer sends out a signal to the engine to go into cold start mode. The fuel is enriched into the cylinders by raisin the idle just a bit placing more fuel into each cylinder, and the idle is advanced by a little electric plunger at the throttle body. Once the engine has warmed, the water temperature sensor sends a message to the computer to take the engine out of cold start mode and into normal run. Now you can understand why the temperature sending unit/sensor is so vital to proper starting procedure. Replace the temp sending unit/sensor and she will work just fine. School's out. Time to go to work.

When the plugs are black and fouled, the engine is getting WAY too much fuel, constantly. Normally, the computer will put the engine into cold start mode when first starting, once warm it cuts back to normal fuel flow. Since it's steadily getting too much fuel, I'd say it's in the computer causing excess fuel delivery. Have the Temperature sending unit checked for proper operation.

Your toyota technician should know what a "cold starting solenoid" is. It is the little thing that works your throttle until the motor warms up and something else takes over. I'd suggest going to another technician.

sounds like it has jumped timing you'll need a mechanic or see your dealer

The issue is one of over-fast idling. First thing is to check coolant level in the engine. Make sure that the coolant is at the 'max' in the reservoir (1:1 mix of water : antifreeze). Low coolant would preve nt the ECU from detecting the car is at operational temperature. When the car is cold the ECU extends injection times to keep the car running but when warmed up the injection times are again shortened to reduce engine speed at idle. Also at idle, the Idle air control valve (IAC) on the throttle opens to allow air to by-pass the closed throttle plate. Check that as the engine gets warm that the coolant hoses to the throttle body become warm (showing that no blockage is preventing coolant circulation). Check that IAC air passage is clear and that valve can open freely. If the IAC coolant hoses are blocked or the valve is jammed open this would account for the very high idle speed. If everything looks OK check the PCV hose from the valve cover to the throttle and make sure that there are no blockages in it.

you car is fitted with a "no fuel"system,so when you take your foot off "no fuel" goes to the engine untill it reaches 1200 revs.then it will allow fuel to flow to keep tickover/smoothness.(its computer controlled)you need to get your car onto the diagnostic computer,(skoda/seat/vw/audi)so you have the codes/items that need to be sorted.The tdi engine was one of the first engines that VW computerised and it is very reliable/powerful,compared to the peugeot/citroen engine.(briefly,the fault is not just a switch/cable),

You need a 10 mil and 8 mil spanner, carb cleaner and mabie some wd40.
Remove the big hose which goes from the throttle body to the air filter housing. Under the throttle body there is a idle control valve, unplug it, spray some wd40 on the 8mil bolts and take them off. Clean the idle control valve and housing and anywhere else which looks dirty, dry it with a lint free cloth and then put everything back on.
remove the battery negative terminal and leave it off for 30 minutes, this will reset the ecu to factory settings.

On the top of the throttle body there is a black circular rubber screw cover, take that off and there should be a plastic screw.

Connect your battery and start your engine, unscrew the idle speed control (plastic screw) so it revs at 2000rpm cold. When the temp needle reached the middle so it revs at 1000rpm hot.

This should solve the problem, if you drive around and find that you in 4th gear, with your foot off the accelerator and the idle is going up and down madly then the idle control valve is worn out and it needs replacing. Cost around £125 on ebay.

This problem can be several things. When your engine is cold, your computer is in a "closed loop" and just pretty much keeps the engine running until warmed up. After reaching operation temperature, the computer starts reading all the sensors. If one sensor is not connected or is defective, you will experience performance problems. Most of the time this will turn on the check engine light, but not always. Second is the fuel pump. This too will cause erratic engine problems.

Hi, Check all vacume hoses and fittings make sure there are no vacume leaks also make sure ignition timing is correct.

What is the engine temperature during this? You state that it starts out OK then develops this problem later.

When you have problems starting it is this after running it or after it sits like all night and is dead cold?