TERRIBLE vibration!!!

[elwesso]

When I am in 3rd gear, and am at about 50mph (RPMs are just short of 2500), theres this real low pitched vibration that shakes everything... It sounds like a subwoofer.... Ive noticed its ***SLIGHTLY*** not as severe when I use better gas (IE amaco ultimate instead of bargain basement).... its not that much, and its probably the placebo affect anyway..... Its been this way for a while, but its gotten worse over the course of my ownership......

So, what do you think this is..... Could it be my knock sensors (known they are bad), dirty injectors (never cleaned, but have used FI cleaner and BG44k)

Also, my idle is too high (probably sticky IAC)..... it idles fine at cold (1250), then it drops down to ~700, then when its fully warmed (driven for about 10mins), its up to 1000...... I had to adjust it higher, because when it was at intermediate it was at 500 and would shake at a stoplight in park...... So I guess what Im asking is whats the factory set for the IAC..... I think Dennis said its something like all the way out, then 6 turns in.....

Thanks........

[elwesso]

Ive driven quite a few miles lately, and it has seemed to have gotten a little better...... It sorta has its good days and bad days....

[louiegz]

I'm not a mechanic, but I do know that a Q is set up to use 91 octane fuel. I always use Sunoco Ultra 94 or Mobil Super.

[elwesso]

I always use 92 or 93 octane......

[maxnix]

There is a TSB that describes this problem in 1995 Q, but I know it occurs in 1994 Q45 also. It occurs in both of mine at slightly different speeds due to different diameter tires.

[Q451990]

Idle should be about 650 if I remember correctly.

Heath

[elwesso]

So the vibration is due to tires??? Hmmm....

Also, heath... If I set the idle lower like that, it idles too low in DRIVE (approx 500).....

[szh]

I had exactly this same vibration in my 1995 Q! At about 50mph in 3rd ... it was relatively minor, so I did not worry about it.

Interesting that it seems to be a commonplace item ...

Z

[elwesso]

Well, I noticed that today at various speeds, it still vibrates some, but not at 50 in 3rd..... It seems to want to do it at just below 2500, but its much worse at 50 in 3rd..... In 1st or 2nd its neglegable, and in 4th Im not sure.....

It is kinda loud, and it doesnt sound right..... Which leads me to believe it might be one of the other things i mentioned.

[Q451990]

Is your car a CA Q? If not it's not a part of the TSB that szhosain mentioned. Check the first set of cats for "Y2" stamped on the heat shield. The TSB mentions the drone at 2250 RPM (50MPH in 3rd and 70MPH in 4th).

The only 1994 Models affected were the CA models, and Federal Models with Active suspension. All 1995-1996 models built before 10/26/1995 with a VIN of JNKNGO1D*TM401749 or lower have the "Y2" catalyst.

The TSB mentions that the drone is created by "engine vibrations transmitted to the body..." so eliminating those vibrations by getting that plenum cleaned, IAC adjusted, injectors flushed, and KS fixed would be my first plan of attack. Hopefully having the ECU running rich due to the knock sensor failure hasn't damaged the cats.

Heath

[Q45tech]

Motor mounts should be changed every 100-120k.Tire vibration frequency is a function of rotation speed.....1,2,even 3 vibrations per tire rpm [radial force and simple imbalance].

The problem is that all tires are not tied together so you could have 4 separate sources times 1 or 2 or 3 vibrations that change phase as the speed changes slightly.........turn the wheel and the front tires change vibration positions.....spin the rear tires slightly and the relative phases change.

All you can do is use a Hunter 9700 to make sure all the tires wheels are below 5 pounds of radial force imbalance and all tires are less than 5 grams of dynamic imbalance.........ALL THE TIME.

[elwesso]

Heath, I got your email..... Thanks.... Funny how you are emailing me, adn I already have all the TSBs..... I need to start checking those.....

And I do hope the cats havent failed either.... I have no idea how long the KS have been gone, but the previous owner didnt anything other than fluid changes..... ..... Is there a telltale way to know if their clogged???

Also, would Joe be able to get me the parts id need to do the TSB......?

And I dont think mine is a CA or Federal model, but I dont know.....

[Aus94Q45]

Isn't this a transmission related issue? What happens to the vibration when you let off the gas? I seem to recall alot of talk about this in many Q's in 3rd gear just shy of 2500 rpm cruising flat on the highway. If it stops vibrating as soon as you let off the gas, I doubt its the tires. There was a thread on this . . . .

[Q451990]

And I dont think mine is a CA or Federal model, but I dont know.....

On the emissions sticker under the hood, it should say something like "complies with all federal and CA emissions regulations for the year manufactured." If it's just a federal, then it'll leave out the CA part.

I'd suspect a transmission mount or exhaust hanger problem before the cats. I'd address those at the same time as the knock sensors. Once you get the engine putting out it's designed horsepower, a lot of other problems will disappear.

Heath

[elwesso]

Well, I checked it out, and it says COMPLIES WITH ALL EPA AND CALIFORNIA EMISSIONS FOR THE 1994 YEAR..... Hmm, now what does that mean?? Are CA models bad???

Ok, so how will I know if transmission/engine mounts are bad......?? The vibration lets off somewhat after I let off the gas.....

[Q451990]

Not bad, just that your car is included in the TSB. Probably not a lot of difference in the mechanicals - just the ECU programming and maybe an additional sensor.

Fix everything else first, then worry about the cats. If the motor rocks much when you rev the engine, they're probably bad. If the transmission mount hasn't been replaced - it's bad.

Heath

[elwesso]

Well.... When I call Joe for my plenum parts, Ill be sure to ask him about the TSB!