: Rough Idle and Stuttering Acceleration



nytwodees
02-02-06, 11:59 AM
I have a 1994 Cadillac Eldorado with the Northstar engine - the mileage is 70,300 miles.

Problem: Beginning about 2 weeks ago my car has started idling roughly. At a Stop Light the car usually Idles smoothly about 600 rpms. Now the car will surge to about 750 rpms and settle back to 600 rpms repeatedly. In addition when I accelerate, the car stumbles and will finally accelerate when I ease up on the accelerator (almost like a bad accelerator pump in the old days). Despite these annoying problems, my car still gets very good gas mileage for a combination of city/highway driving.

I brought my car to my favorite mechanic. He checked the car with his computer and did not find any problem codes. He removed the new gas filter and checked it for any obstructions but found none. He checked 2 of my spark plugs (platinum tipped) and said they were perfect. He checked the coil or its equivalent and said it was OK. He said that the 1st thing he would do is change the spark plug wires.

I have added dry gas and fuel injection cleaner to my gas, suspecting I might have gotten a bad load of gasoline. This did not remedy the problem.

Does anyone have any suggestions as to what might be causing my problems. Your help will be greatly appreciated. Thanks!

Dan

Ranger
02-02-06, 12:15 PM
I would suspect wires.
http://www.cadillacforums.com/forums/showthread.php?t=25119&highlight=stutter

acklac7
02-02-06, 01:43 PM
I have a 1994 Cadillac Eldorado with the Northstar engine - the mileage is 70,300 miles.

I have added dry gas and fuel injection cleaner to my gas, suspecting I might have gotten a bad load of gasoline. This did not remedy the problem.


Dan


Be carefull when adding a solvent based fuel injector cleaner, as the solvents can/will kill your fuel pump :(....Always use a non-solvent based cleaner, such as lucas fuel treatment ...And I wouldn't run it on/near empty for at least 3 fill up's ;)

EcSTSatic
02-02-06, 01:45 PM
Wires could be bad but if you did get some bad gas then your filter is probably fouled up. I'd replace it if I was you.

I had a similar situation on my TurboCoupe. The throttle position sensor was bad but it did not throw a code.

Let us know what happens. We're here to learn.

Krashed989
02-02-06, 07:00 PM
I think you have a good mechanic.

I would also suspect it to be the spark plug wires.

nytwodees
02-05-06, 01:40 AM
My mechanic replaced all the ignition wires today with genuine AC Delco replacements. Unfortunately there was no change and the car is still idling roughly and stumbling upon acceleration. Any other suggestions?

Krashed989
02-07-06, 12:18 AM
Well the next thing to do would be to find out what cylenders aren't firing. You can do that with one of two ways. The first way would be to just pull each spark plug wire off one by one with the engine running (re-attaching each one before moving to the next). To try and see which one Least affects how the engine is running.

OR, You could tell him to go into diagnostics mode with the engine running. Then when it gets to "PCM?" press the fan up button to go into that submenu. After that press the fan down button untill you reach "PCM OVERRIDE?" then press the fan up button to enter that submenu. Once in there press the fan down button again until you reach "PS04" (injector disable) On the climate control LCD display it will show you what injector you're messing with. The cooler (blue) button will disable that injector for the duration that you hold the button down, and the warmer (red) button will make you select the next injector. Go through each injector and disable them one by one to see which one has the Least effect on how the engine is running. If there is more than one cylender that isn't firing, take note of what ignition coil is running them. If the misfire is sporadic and in all of the cylenders, check your FPR (Fuel Pressure Regulator). If you use fuel injector cleaner too often it may have eaten away at the diaphram in the FPR and caused this problem.


To check the FPR you have to remove the plenum/beauty cover and look at the fuel rail. The FPR on your car will NOT have a vacuum hose going to it because it's inside of the manifold and doesn't need one. After the plenum is off, DO NOT start the engine. Instead just turn the key to the "ON" position to pressurize the fuel rail, and see if fuel leaks out of the vacuum nipple on the FPR. If any fuel at all comes out, the FPR is bad, and needs to be replaced.

Hope this helps.