slayrdave Posted July 6, 2009 Report Share Posted July 6, 2009 My 91 Deville DTS with 72k miles has a rough Idle. My MPG started started declining so I changed the plugs. Did I forget/do something wrong? No Check Engine Light and the MPG has improved. I am using 91 octane. However , my parents may have used 87 octane when the price of gas was high. Rough Idle shakes the steering wheel/car Link to comment Share on other sites More sharing options...
BodybyFisher Posted July 6, 2009 Report Share Posted July 6, 2009 My 91 Deville DTS with 72k miles has a rough Idle. My MPG started started declining so I changed the plugs. Did I forget/do something wrong? No Check Engine Light and the MPG has improved. I am using 91 octane. However , my parents may have used 87 octane when the price of gas was high. Rough Idle shakes the steering wheel/car What engine 4.9? Check the distributor cap, rotor, check the ignition wires 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...
Ranger Posted July 7, 2009 Report Share Posted July 7, 2009 DTS? The DTS didn't come about until 2000. Recheck the firing order. You may have crossed a wire. Link to comment Share on other sites More sharing options...
slayrdave Posted July 24, 2009 Author Report Share Posted July 24, 2009 DTS? The DTS didn't come about until 2000. Recheck the firing order. You may have crossed a wire. Sorry- Deville Touring Sedan with 4.9V8........I have replaced plugs, Ignition Wires,Cap,Rotor ,and Fuel Filter.I'm sure I don't have a wire crossed. Car still has a rough idle. Almost feels like it hesitates when you first get on the gas. Could it be a sensor or catalytic converter ? still no check engine light... maybe the coil? Link to comment Share on other sites More sharing options...
Ranger Posted July 24, 2009 Report Share Posted July 24, 2009 DTS? The DTS didn't come about until 2000. Recheck the firing order. You may have crossed a wire. Sorry- Deville Touring Sedan with 4.9V8........I have replaced plugs, Ignition Wires,Cap,Rotor ,and Fuel Filter.I'm sure I don't have a wire crossed. Car still has a rough idle. Almost feels like it hesitates when you first get on the gas. Could it be a sensor or catalytic converter ? still no check engine light... maybe the coil? I recall our old Guru once mention that a bad TPS would act like that. Somewhat like a bad accelerator pump on a carburetor. Link to comment Share on other sites More sharing options...
slayrdave Posted July 29, 2009 Author Report Share Posted July 29, 2009 DTS? The DTS didn't come about until 2000. Recheck the firing order. You may have crossed a wire. Sorry- Deville Touring Sedan with 4.9V8........I have replaced plugs, Ignition Wires,Cap,Rotor ,and Fuel Filter.I'm sure I don't have a wire crossed. Car still has a rough idle. Almost feels like it hesitates when you first get on the gas. Could it be a sensor or catalytic converter ? still no check engine light... maybe the coil? I recall our old Guru once mention that a bad TPS would act like that. Somewhat like a bad accelerator pump on a carburetor. My mechanic has discovered #3 cylinder not firing.No voltage from the ECM for that cylinder(injector). Suggest new ECM. Can anyone relate? Link to comment Share on other sites More sharing options...
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