: P0300 and just filled coolant

01-13-09, 10:45 AM
Two weeks ago, my Mom's 98 Eldo was missing a little at idle. A few days later she tells me she has a low coolant level, so I add coolant and it took a whole gallon. That concerned me? Now it has a service engine light and running rough at idle. I had the code pulled and it's a P0300-Random Cylinders. I had two coil packs replaced at an out of state dealership last year when it had a similar problem. While driving it this morning it had a rough idle but when I got back home and put it in park, it ran smooth? Do coil packs go bad or intermittant? Please give some place to start.

01-13-09, 12:18 PM
Start by having the coolant tested for the presence of exhaust gases. It has all the symptoms of a bad head gasket. DO NOT test or have it tested soon after added coolant. You'll get a false negative.

01-14-09, 12:25 PM
Yep - HG