: Throttle Body, Rough Idle



akaz87
03-02-04, 12:08 AM
Hey, My 1998 STS with 100k miles has a slight rought idle. It has all its normal power its just a rough idle. Someone said it could be the throttle body with to much build up carbon. Can someone explain how to clean this? I know where its at but I'm not sure if I can just pull off all the wires. When I'm driving the car seems to shake a little, i'm not sure if its the idle or the gas, or the tires. I am going to buy new tires to see if that helps. Well If anyone can help that would be great!

Thanks

BeelzeBob
03-02-04, 12:05 PM
Read the post above http://www.cadillacforums.com/forums/showthread.php?t=9007 for some more info.


There is a misfire diagnostic on your system that should be turning on the SES if there is a misfire. If you have no SES light then it is probably running fine.

Cleaning the throttle body is a good idea and will prevent a sticky feeling throttle but it likely will not help the idle quality.

You might also remove the EGR valve and clean the passage in the base of the valve and the shaft of the pintle inside the passage in the base. The valve may be sticking open slightly and causing the rough idle. Do not let solvent run into the can of the valve (down the shaft) as it will ruin the valve by eating the insulation off the wires inside.

Is this just starting or is it a "new" car to you that you are feeling this roughness on??? 98 STS's had quite a few idle quality complaints as the idle isolation of that platform (new for 98) was not as good as previous and the slight "quiver" that the 300 HP engine has due to the Hi-Perf cams would cause the car to shake very slightly at idle. The roughness you feel at highway speeds is likely tire induced. Those cars were very sensitive to tires and tire imbalance and lateral force variation. A set of Michelin tires is the simple fix usually as the Michelins typically have the most uniformity of any of the performance tires.

akaz87
03-02-04, 09:11 PM
Read the post above http://www.cadillacforums.com/forums/showthread.php?t=9007 for some more info.


There is a misfire diagnostic on your system that should be turning on the SES if there is a misfire. If you have no SES light then it is probably running fine.

Cleaning the throttle body is a good idea and will prevent a sticky feeling throttle but it likely will not help the idle quality.

You might also remove the EGR valve and clean the passage in the base of the valve and the shaft of the pintle inside the passage in the base. The valve may be sticking open slightly and causing the rough idle. Do not let solvent run into the can of the valve (down the shaft) as it will ruin the valve by eating the insulation off the wires inside.

Is this just starting or is it a "new" car to you that you are feeling this roughness on??? 98 STS's had quite a few idle quality complaints as the idle isolation of that platform (new for 98) was not as good as previous and the slight "quiver" that the 300 HP engine has due to the Hi-Perf cams would cause the car to shake very slightly at idle. The roughness you feel at highway speeds is likely tire induced. Those cars were very sensitive to tires and tire imbalance and lateral force variation. A set of Michelin tires is the simple fix usually as the Michelins typically have the most uniformity of any of the performance tires.
I've had the car for a while. Now it is doing this rough idle. In the last 3 months I've replaced the FPR & Fuel Pump. I need to get a socket that will fit the bolt for the EGR Valve. Should I clean out the Throttle body? Isnt it kind of a Pain in the ass on the 98's? The fuel lines right over it, and its hard to get to. My idle isnt horrible, its just annoying. It does seem to run a little bit funnyer then normal, just not normal, I cant put my finger on it.

akaz87
03-02-04, 09:12 PM
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