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Discussion Starter #1
Does anyone with rough idle or engine vibration problems notice variations in sound?

When I bought the '99 in February, it sounded like it wanted to stall at stop lights but it rarely does this now....made me think it was a vacuum leak.......

At other times the vibration sometimes gets so strong the bumper makes a strong rattling noise...but the idle seems to be fine.

At other times, which is more frequent now, I'll sit at a red light and hear a cyclical humming sound...with vibration.... (like clothes in a dryer though it doesn't 'actually' sound like that....the circular repetition, however, makes me think of this analogy)....This is the sound I'm most curious about...

When I first opened the hood, I used to hear maybe a hissing sound, like something kept switching on and off in the engine when it idled....but it's been a couple months and I haven't heard it anymore.....again....makes me think vacuum leak, but I haven't heard it since winter.

Something else I've noticed.....

When I first start the car in the morning, it races really high at the turn of the key (like I've given it gas even though I never step on the accelerator) and is abnormally loud....but then the engine gradually drops back down to a quieter idle......

But it doesn't stop there....

As soon as I get it out of the driveway, it wants to jump out of the gates and I always wonder, when I stop at the first stop sign 50 yds in either direction, if the car will actually stop. I literally have to press down hard on the brake pedal out of fear it won't stop. As soon as I let up on the brake pedal, the car wants to go. After a few more stop lights, it seems fine...but it always does this when I first start out.....

(mod edited - added content from another post of the OP)
 

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first, you have to check for vaccum leaks, down the throttle boby (TB) you have a hose from the purge system, check the integrity of that hose.

also check the PCV valves, from the exhaust manifold to the intake manifold.

also check the EGR valve, maybe it´s stuck you have to clean it.

about the first start and the car rise the RPM it´s normal when but only about 1000 rpm, then it drops to 750-800 rpm, this thing it´s the funtion of the IAC (Idle air control) valve.

about the hard brake, you have a vaccum leak in the brake booster, i think this is the biggest problem, because if you don´t have vaccum in the booster the pedal are very hard so check this thing first, check the hose boostr, check the booster it self, if you push the brake pedal and heard a sound like "sssssssssssssssssss" then you have a broke diafragm booster, you can repair it or just put a brand new booster.

remember chek the booster first for safety and to prevent the high idle.

keep post it you problem
 

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I've got rough idle in my 99 as well. I've replaced the PCV valve, some vacuum hoses, cleaned the throttle body and idle controller, I cleaned out the combustion chambers, ran fuel injector cleaner through it, had the fuel pump replaced, and did a tune-up on it. I have some lifter clatter so I'm thinking my lifters may be shot.
 

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That sound is probably just the harmonics in the exhaust system. Mine does the same with the same bad idle, even worse when the cooling fan kicks on.
 

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Discussion Starter #6
I've got a redundant "service engine soon" again and it's probably related to the IAC. The IAC itself looks pretty clean and the gasket is in pristine shape. I've soaked the IAC twice and the light goes off after I reinstall it. It doesn't make sense but if the IAC is failing....it probably explains why I have such a rough start. The PCV is fine, rattles good, but a little oily/greasy on the end so I cleaned that off. My setup doesn't have the elbow like the '98 did. I don't know much about the vacuum hose setup. All I know is I couldn't pry the vacuum hoses off the intake manifold. The PCV vacuum consist of metal tubing that I don't want to break by trying to twist it off. It doesn't make sense to me when people say "pinch" of the vacuum hoses when testing for certain things since there appears to be metal tubing inside the hose. I'm not sure where to disconnect the EGR valve. The Haynes manual shows it being disconnected from the exhaust. It looks like I could simply unbolt it right below the value and then undo the two screws. I can probably get to the throttle body okay. It's got a little bit of a coating of carbon buildup from what I can see when I remove the IAC
 

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Discussion Starter #7
Had the code checked, it's P1506 again. P1504 didn't show up this time. It idles very nicely right now like it did a month ago when I unhooked the electrical component to the IAC.

I forgot the brakes part....feels like I have ABS even though I don't. I might not be describing it accurately in my previous post.... It's more like the engine doesn't want to slow down and I have to hold the brakes down to prevent the car from lurching ahead....only when I first start out. Could be IAC related......

It's going to be a bit before I can do compression checks and vacuum tests. When I do, I'll post the info.

I've got to take care of the leaking gas tank when I fill it...............
 

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replace the PCV valve, even if it seems "OK"
 
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