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Engine Misfire?

Hello good people. I have '94 Olds that has been acting weird since I bought it almost a year ago. When I start it in the morning, it runs fine for about a minute, and then the engine starts shaking, as if the car is about to stall (while still in idle). After a few seconds of shaking, the engine revs itself as if I’m pressing on the gas, and the problem goes away for the rest of the day (even when I start after leaving work). If I don’t allow it to “shake” while in idle, and start driving right away, it will do the same after a minute or so, i.e., it doesn’t respond well to pressing on the gas. Recently, the problem has been occurring throughout the day. I had it tuned up (new spark plugs, wires, PCV valve, air and fuel filter). I also replaced the fuel pump when it went bad a couple of months ago. Any thoughts on what the problem is? Thanks much for your help.

Suspect the idle air control valve.
Here is more information about the idle air control valve. http://www.autozone.com/autozone/repairinfo/repairguide/repairGuideContent.jsp?partName=Idle+Air+Control++IAC++Valve&pageId=0900c152800cc507&partId=0900c152800cc507 At www.autozone.com. Go there and register, and you can see the information. Let us know if you have any difficulty seeing the information.