2003 3.4 impala vibrates (not shakes, vibrates) at low RPMs

[sbpr]

2003 3.4 impala vibrates (not shakes, vibrates) at low RPMs I've got a 3.4 impala,~195,000 miles. Symptoms: The car vibrates at low RPMs, when slowly accelerating, or holding speed. If I rev hard it doesn't vibrate, if I coast down, it does not vibrate. In addition, when I am stopped and idled at a red light, it _was_ vibrating, but I changed out the spark plugs and wires, and it's better but not fixed. Pre-plugs, it was really bad - to the point where I thought the car might explode.@_@ Post-plugs, it's annoying, but functional. That said, I don't want it to worsen again to the point I'm worried it's going to explode again (really really really loud), so I'm trying to fix it, not just mitigate. Any suggestions?

[oldblu65]

Sounds like a possible vacuum leak on the engine . Open the hood with the engine running and listen for a " hissing " sound , being careful not to come in contact with any hot or rotating components ! The rubber hoses on the engine deteriorate with age and the many heat cycles they go through , and break or crack , causing the engine to lose vacuum and it causes the engine to run terribly at idle or low engine rpm's .

[sbpr]

standard disclaimer: i am not a car person. Most of this stuff is pretty new to me, it took me a week to do the spark plugs and wires because I had to ratchet up the engine. That said, I like to do it myself when I can, and once I did it, I know it pretty well. So - uh, which one are the vacuum lines and how do I identify them? ^^;

[oldblu65]

Vacuum lines are generally black in color and range from about 1/8 " up to maybe 1/2" in size . There are a few exceptions where a small plastic line will be used for the majority on the length with short rubber lines used to attach the ends to the components . Most often they are slipped onto fittings with no clamps or devices to hold them in place as they are under vacuum instead of pressure . They are essential to proper engine operation and must be installed in the proper location for everything to work as intended . If you get them mixed up and install them in the wrong place , the engine will run terribly , perhaps not at all ! Always make notes or digital photos so you'll have a reference to go back and look at if you become confused ? Generally , don't remove more than one at a time to limit your chances of making a mistake on where each one goes . You could take it to your favorite auto parts store and get one of the knowledgeable and experienced guys to show them to you . They may even be able to show you if any vacuum lines are in need of replacement or if any have become disconnected or are missing . I think I have a diagram ( somewhere ) of the vacuum line layout but will have to try to locate it ? If I can find it , I'll try to get it to you . I did find a link to the needed diagram , not sure if it's the correct one for your particular application , but try the link ( http://www.mechanixtrix.com/article/...?articleid=176 ) . If the link doesn't work , I'll need an email address to send a copy to you . When received , make a copy of it and take out to your vehicle and see if it matches your layout before removing any lines !

[sbpr]

Ended up taking it in to firestone, the vacuum lines were a little too much for my current automative DIY skills. Anyways. It wasn't the vacuum lines at all - it was the exhaust not giving enough backpressure. I'm out $600 for that, but hopefully this info helps the next dood.