Vibration at idle, What to try next?

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avu3

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I've had a vibration at idle since I bought my 95 at 45K miles in 99. The dealer did work on it, not in relation, that had no effect. They rebuilt the heads and replaced the cams/timing chains/tensioners.

Since then I have replaced the IAC, Plugs, wires, O2s with no effect. I've also cleaned the Maf and throttle body a few times. None of those things ever changes it.

The only other suggestion I have had is motor mounts, but those are a real pain to replace. I've poked at them and I have no indication they are bad.

Does anyone think I might have missed something that could be easy to fix?

That vibration really ruins the car, which I've noticed more and more having to drive a tow-rus while I wait to fix the Mark from the dog incident...

Scott
 
RE: Vibration at idle, What to try next?

That's really a stumper. My old '96 Mark VIII with 100K was so smooth at idle that I'd often have to look at the tach when at stoplights to be sure it was running. My '97 isn't quite as smooth, but still barely noticeable. Is it like a steady, single cylinder miss? Does it go away at slightly higher rpm? Have you had a shop put a scope on it so see if all the plugs are firing good at idle?

John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L
 
RE: Vibration at idle, What to try next?

Did you remove the air silencer? I noticed that mine doesn't run rough necessarily, but it doesn't run as smooth as it used to before we took the silencer out.
 
RE: Vibration at idle, What to try next?

My vote is for motor mounts.
P.S. How is completely redoing a head not tough,but replacing motor mounts is???????
 
RE: Vibration at idle, What to try next?

My vote is for motor mounts.
P.S. How is completely redoing a head not tough,but replacing motor mounts is???????
Click to expand...

When someone else does the heads, and you have to do the motor mounts yourself.
 
RE: Vibration at idle, What to try next?


When someone else does the heads, and you have to do the motor mounts yourself.
[/quote]

I couldn't have said it better myself.... They did the heads because it had a tapping, and they found a valve seat damaged. I would have to do (or pay for) the motor mounts...

I did recently remove the silencer, but that had no effect.

The vibration is not like a cylinder miss, its just rought. It is in a particular RPM range, from just off idle up to about 900 rpm. Above that it smooths out. I can affect it a little and get periods of smooth by turning off the hvac and causing the compressor to cut out, but it will eventually come back, compressor on or off.

I have not had a shop put a scope on it. I have never gotten decent service from an auto mechanic nor found one I trusted... I guess its time to give that a shot...

Scott
 
RE: Vibration at idle, What to try next?

Motor mounts would not be that hard.. youi have to drop the K memeber. While you have the K memeber down, might as well put a big swap bar in there, along with some headers. Once the K member is dropped the motor mounts are ultra easy to get to.
 
RE: Vibration at idle, What to try next?

That was going to be my next questions. I have no lift or hoist... how hard does that make a motor mount swap? I would assume you have to relieve pressure off the mount to change it.

And, were I to do that, I would replace the sway bar. Good point.

Scott
 
RE: Vibration at idle, What to try next?

Scott - I personally don't think bad motor mounts would cause what you're seeing. If a car's running smooth, it's not going to vibrate just sitting there, even if the mounts are bad.

I'd be willing to take a run up there this Sat. or Sun., just to see if two heads together might be able to come up with something. I don't really have any equipment other than tools and a multimeter, and I've only got tech info for '96 and newer, but if you want, I'm game...

John
http://mark8.org/users/johnaec/Mark_VIII_s.jpg
'97 Mark VIII LSC
'96 T-Bird 4.6L
 
RE: Vibration at idle, What to try next?

Thanks, John. The next two weekends are no good. We have to get the race car off to paint, and still need to get the new brakes on and a few other odds and ends. That's saturday - then Sunday we have to get it down to SJ for paint.

The following weekend I have family in town. Maybe the weekend of the 7th.

It's not an urgent/panic thing. I've lived with it for four years, I just thought I might see if anyone had any new ideas for me.

Scott
 
RE: Vibration at idle, What to try next?

Take a look at your harmonic balancer. If they replaced your timing chain, they removed/replaced it. It may be loose, installed without the key, or the rubber may be disintegrating.
 
RE: Vibration at idle, What to try next?

Mazda RX-7 in NASA and SCCA. We get to run Thunderhill, Willow Springs, Sears Point, Button Willow, the new Reno Track, California, Las Vegas and Phoenix.

We've just about got the car done, it just needs paint, the dash fabricated (we need the window out, part of paint) the front suspension and to replace all the rubber on the motor.

Scott
 
RE: Vibration at idle, What to try next?

No, I won't be at the nascar race... too much of a circus for me. It'll be august or sept before we get on track. They just ran at Inferior raceway this weekend.... had a huge crash and had to fly a guy to the hospital. He's going to be ok.

Coilpacks... Yeah, but before I got replacing things I probably need to find a decent mechanic with a scope...

Scott
 
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