Check engine light goes on then RPMs go crazy

1998 Cherokee Sport 152,000 miles. Recently I was driving and the engine just started reving. It was going around 60 then took my foot off the gas to coast and the car jerked and then the RPM started flucuating between 2000 and 3000 rather violently. The car jerked a good amount but the speed stayed constant. The check engine light came on so I took it to an oil place where they told me the code said it was a gas gauge problem but it would not affect the engine. He also said the throttle casing was dirty and that he cleaned it. He turned off the check engine light and then about a week later it started up again. Any ideas on how to fix it. It feels like I am giving it quick bursts of gas, which is a real issue in traffic as I think everyone thinks I want to race. It went away for about a month and then came back last night.