Cadillac Repair: 97 Eldorado - Enging running Rough, mileage engines, ac delco

Question
I have a 97 Eldorado that has recenlty been ideling and running rough.  We changed spark plugs and wires plus the air filter....no help, actually runs rougher.  At a stop you can feel it a bit as though its missing.  Any thoughts on what to check next?

Answer
Hi Diane, Since the engine seems to run rougher than before I would recommend checking that the sparkplugs are tight enough in the holes. Usually 15-20ftlbs useing a torque wrench on a cold engine would work. Then make sure that the plug wires are routed correctly.   

   When you had the wires off if 1 or more coil towers where the sparkplug wire attached showed signs of rust the coil might be arcing. You could try to clean the terminal with steel wool otherwise I would suggest replaceing the coil and see what happens. On the subject of sparkplugs there are 2 brands that I don't seem to have much luck with and will actually make a GM engine run rougher. If you installed Autolites or Bosch plugs I would take them out and install the AC delco platinum plugs and the running problem could be solved. There is a possability that a plug may have been cracked eithor before or durring installation and after running for a couple hours sometimes you can see a dark line where the crack is.

    There is a possability that one or more injectors could be restricted and running some injector cleaner into the gastank might help after a tank of gas has been used. I would recommend useing the Valvoline Extreme...I think that is what its called...it will say for high mileage engines.

    Past that if it still runs rough there is testing that would need to be done to determine where the problem is. It could be spark related such as one or more coil terminals aren't sending a spark to the plugs. The oxygen sensor could be staying in the rich or lean setting. Checking for codes and useing a scan tool to look at the engine data might lead to the fix. Also monitoring fuel pressure might determine that the fuel pump is weak, an injector is leaking or not working propperly or the fuel pressure regulator is leaking fuel to the vacuum hose. That last thing is easy to check. Take the cover off the engine like when the plug wires were replaced and you will see the fuel pressure regulator in the fuel rail attached to the vacuum hose. Remove the hose and see if gas comes out. If so then it needs to get replaced. If no gas then turn the key to light the dash lights  several times to allow gas to pressureize the fuel rail and then see if you get fuel.

    Try those things and hopefully something will show itself. Let me know if you need more help. Bill