If its computer controlled engine, it more than likely a dirty or bad Idle Air Control Valve.
my 1990 300zx is idling rough what could cause this?
Any number of things could cause your vehicle to surge. You need to take your vehicle to a tune-up shop and have it diagnosed.
clean your injectors.
Bad EGR valve
Home Again with Bob Vila - 1990 Surge Protection Plumbing Bamboo Blinds and Garden was released on: USA: 10 December 2005
Yes it is - only when idling and if I turn the heater on it cools down - thermostat?
Engine idling in Park. Pull dipstick and read the level.
A 1990 Suzuki Samurai may flood while idling due to several reasons, including a faulty carburetor that allows too much fuel to enter the engine, a malfunctioning choke that remains closed, or issues with the fuel delivery system such as a stuck float. Additionally, worn spark plugs or ignition problems can prevent proper combustion, leading to an overly rich fuel mixture. Ensuring proper tuning and maintenance can help resolve these flooding issues.
If the engine is revving high and low while it is idling, then that can be the idle air valve (what was told to me by a professional). I don't know if it can fix itself because I had mine hibernating for about a year and it stopped.
It could be a vacuum leak in the throtle body or intake manifold. Get some carb cleaner and check it. Be careful as the cleaner is flamable.GoodluckJoe
why is my 1990 305 gmc idling rough when on the gas peddle runs great
There are several things that can cause your 1990 Volvo 740 to stall while driving. The most common cause is a bad fuel pump.