OK, I've searched and I've found a couple of my symptoms in other posts, but nothing that hits them all.

Last week my car started to have an electrical and RPM problem. I'll be driving and every ten seconds my speedometer and RPMs will dip down and then come back up. Speedometer will dip by 10 mph or so and RPM will drip by 500rpm or a little more. Also, my cruise light comes on. If I have the cruise on, it disables it. My RPM dips enough that if I'm sitting and idling, the dip will kill the engine.

My check engine light has been on for a year. The code reader said that my ECM was bad. I didn't have the money to replace it at the time, and for a year, I didn't notice any consequences for a bad ECM. Until now.

Also, I turn my key to the ON position, and every ten seconds there will be an electronic rrrrrring sound from the engine and two codes will come up on my display. One is 601 (i think) (Bad ECM) and the other one is 1684 (i think) (The battery has been disconnected within the last 50 starts). The 1684 code doesn't make any sense since I haven't disconnected my battery lately.

Sorry for being chatty, I just can't figure out what is wrong with my car.

 

For about $200 you can replace the computer. Search on eBay for a service that programs the new computer with your mileage and VIN.

Check carefully for a bad ground somewhere. Occasionally, a bad ground can result from corrosion. To have a good electrical ground, there must be good metal-to-metal contact. That means the electrical connector must penetrate the paint and hit metal underneath. This can result in corrosion developing after a number of years, especially in the presence of electrical currents.