1995 gmc suburban idles rough

Answer 1

There are a number of reasons for a rough idle. Best to do a standard tune up. This includes new plugs, wire set (plug wires), pcv valve, distributor cap and rotor, oil change, air filter, fan belt or serpentine. While you are doing this look for any sign of a vacuum leak. First I do the rotor and the cap followed by a timing adjustment, then I like to do a full compression test on all cylinders. I usually do this as I am replacing plugs. If compression looks acceptable than I will continue to doing a vacuum test after new plugs are put in. Vacuum is often where you find the problem. A vacuum will tell you if you have a vacuum leak, but it will actually give you a very large diagnostic view of how your engine is breathing and running. If the vacuum test looks good, and you are still idling rough, clean your carb or throttle body for fuel injection. With carb you can make necessary adjustments if you handy with carbs. In case of Fuel injection you can clean the throttle body like a carb, by spraying carb cleaner inside. Read then can and follow the instructions. Be careful because especially with fuel injection not all parts should be soaked real hard and the spray is highly flammable so use care around the hot parts. There is the possibility of needing new injectors, or it could require an overhauled carb. Also there are various sensors that communicate with the ecm on engines with computer. These sensors can cause a lot of hell on an idle and on overall performance. O2 sensor is a relatively cheap and easy to access sensor that can cause a lot of problems. Also, I have seen idle problems related to temperature. For instance a vehicle I once had had a thermostat that was too low, a 160deg instead of the 195 deg. It caused high idle because the engine never thought it was warm enough. There a lot of things that can cause idle troubles. Good luck. Start with the basic stuff and work yourself through it. Good luck.