Hello, I have a 1990 regal that one day just out of the blue started running rough when it warms up, I have pulled plug wires to see if I am dropping a coil, so far to no aval.

What other ideas does anyone have to check next, I was thinking Converter overheating (creating to much back pressure) injectors, and fuel filter.

any help would be appreciated

Thanks Doug

On these cars, rough running once warmed up is caused by one of three things.

1. Ignition component heat-sinking (ICM, crank position sensor, cam position sensor if equipped, ignition coil, etc...)
2. ECM failure (it's mounted under the hood)
3. EGR valve not opening, throwing off air/fuel ratio

Thanks, where are these located and is there a test I can perform on them.

I have had a similar condition in the past and replaced a coil, but that did not solve it so I put a ignition module in and that was it, so I have an extra good coil to use it that is it.

I just am not familiar with the ECM (and its location) and where the EGR valve is (1st time having to deal with one)