Check the Idle Air Control, it controls the idle speed of the engine.
Why Does My Truck Idle High In Park?
Why does my 2000 ram 1500 idle high in park and a little when I'm driving down the road but not all the time
If your car has fuel injection, the IAC, idle air control, a sensor that the computer controls, could be bad. You need to have a mechanic do a scan on the vehicles electronics and see if there is a code stored in the computer. Pep Boy, Sears and other places usually do this for 35 to 50 dollars. They diagnois the problem and you can go from there as to let them fix or yourself do the repairs.
Check for vacuum leak and check timing for your hard start problem
While I was driving today my rpm gauge suddenly went up and my car made a funny sound. It jerked a little then went back to normal. Should I be concerned?
I hate to tell you this, but your problem sounds very familiar to something that just happended to me. I'm drivng down the highway and all of a sudden my rpm's shoot up and come back down. As it turned out, the transmission was angageing and disengageing. In other words, my transmission was on the blink, and it is going to cost me $1400 to get it fixed. If your rpm keep going up and down while driving, check to make sure that your transmission is still engaged. One way to tell is to see if your speedometer is still marking your speed, if not, well, there you have it.