jdelhorbe Posted November 7, 2006 Report Share Posted November 7, 2006 I had a rough idle problem that turned out to be 1 bad coil. I replaced the coil and the problem went away. The car is a 1993 STS with 57,000 miles. Looks like old age or high miles can cause problems. I found the problem using a $10 VOLT/OHM meter from Radio Shack. I checked the spark plugs and spark plug wires with the ohm meter and found they were ok, i.e. the resistance was within specs. I then checked the voltage output of each coil with the volt meter and found 1 coil was only putting out 20% of the volts of the other 3 coils. The car ran/started/idled ok even with the bad coil, but power and MPG was way down. I had a clogged EGR valve on the same car last year and the symptoms were different. The car would stall at idle and was very hard to start. I hope this informatiom helps others who have similiar problems. I read all the posts on rough idle problems from the last 2 years that were posted on this board. They helped me determine what the problem was without replacing parts at random. Link to comment Share on other sites More sharing options...
BodybyFisher Posted November 7, 2006 Report Share Posted November 7, 2006 I had a rough idle problem that turned out to be 1 bad coil. I replaced the coil and the problem went away. The car is a 1993 STS with 57,000 miles. Looks like old age or high miles can cause problems. I found the problem using a $10 VOLT/OHM meter from Radio Shack. I checked the spark plugs and spark plug wires with the ohm meter and found they were ok, i.e. the resistance was within specs. I then checked the voltage output of each coil with the volt meter and found 1 coil was only putting out 20% of the volts of the other 3 coils. The car ran/started/idled ok even with the bad coil, but power and MPG was way down. I had a clogged EGR valve on the same car last year and the symptoms were different. The car would stall at idle and was very hard to start. I hope this informatiom helps others who have similiar problems. I read all the posts on rough idle problems from the last 2 years that were posted on this board. They helped me determine what the problem was without replacing parts at random. This is VERY interesting, can you detail how you checked coil voltage with a volt meter? What range? Do you think there is a danger of shocking yourself? Did you notice if the wire arched through? Can you explain how you did this? thanks, Mike Pre-1995 - DTC codes OBD1 >> 1996 and newer - DTC codes OBD2 >> https://www.obd-codes.com/trouble_codes/gm/obd_codes.htm How to check for codes Caddyinfo How To Technical Archive >> http://www.caddyinfo.com/wordpress/cadillac-how-to-faq/ Cadillac History & Specifications Year by Year http://www.motorera.com/cadillac/index.htm Link to comment Share on other sites More sharing options...
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