1996 vw golf 1.8 se Idles roughly when warm only

There is more air taken in. Combined with the progressive fuel supply after starting, this results in high refs. When the engine gets warm or the extra fuel supply stops, the engine runs lean. To the extend where combustion stops. Riding with an air leak is ill advisable. Check everything related to air intake. Usually the rubbers right before the engine become brittle and crack or perhaps the metal strap around them failed to hold them on. It is called a vacuum leak.

check spark plugs and distributor. look for bad wear and missing parts. It must be a faulty spark plug which is not igniting fuel in one cylinder. If you decide to replace the plugs its best to change all of them.

a car of that year should have an ecu controlling fuel air mix etc. this normally controls the timing.
To reset the ecu on my '95 VW Golf disconnect the battery (negative / black terminal) for 15-30 minutes depending on who you ask. So I do 30 minutes.
If it has central locking make sure you don't leave the keys in the car when reconnect it. swich on the ignition without starting the engine so the dash lights up with the oil light etc. for 30 seconds then off for 10 seconds. then start your car. It will relearn so it will run a bit rough for a while but should settle down. take it for a spin on different types of road ie. slow and fast.

hi RAF340 have you found the solution to your car coz my polo doing the same thing and i cant work out what it is. HELP ME PLZ

Best advice is buy an Official VW Repair Manual by Bentley, Publishers for your specific year and model. It is available from your local VW dealership network and most VW independent repair shops as with other VW internet web sources.

You must have bad ignition wires. The high voltage electricity must be leaking out of the boot(s) and arching from the moist air surrounding the coil pack.
Use a spray bottle filled with tap water. Set the nozzle to mist and not stream, you want to have a misting effect. With the engine running, spray at the area of the spark plugs, wires and coil pack. Do this in a dark area so you can easily see if any arching is produced. Observe while spraying water if the engine starts to run rough. If it does you definitely have an electrical leak and need to repair or replace that part. Some people apply JB Weld epoxy to a cracked ignition coil pack housing, I would just replace the coil because it can cause misfiring of a cylinder and ruin your catalytic converter. For a 2.0 AEG engine it would cost about $70 for the part. If it were the ignition wires, they usually cost the same price.

if it works leave well alone,lots of cars appear noisey in reverse with a manual gearbox

have you tried reseting the computer
disconect the batery and wait 5 mins then re conect the baterie

try changing distributor cap & coil

have the fault codes read to get the problem area