Brief : My engine has an extra wobble, and a new sound of something grinding/vibrating/churning, that is especially "wobbly" when the engine is cold. My intention to replace the belts, one by one, starting with the timing belt.

Long : 1991 240 SE Station Wagon, automatic. Her engine is in good shape, until recently when she started producing a strange grinding/straining/churning/vibrating noise and the engine (for lack of a better description) wobbles more. The only consistent moments are these:
... if the engine is cold, it wobbles the most. One the engine has time to warm up (thermostat to 50/50), there is no wobbling.
... if the engine is cold, the grinding/straining/churning/vibrating noise happens the most often. It happens in idle, ceases almost entirely when I change to reverse, and then reappears when I change to drive.
... once the engine is warm, the noise goes almost completely away, except for under stress (e.g., downshifting to power up a hill).

The grinding/straining/churning/vibrating noise, as best as I can describe it, really sounds like a noise & vibration belts would make when loose or such. Like, a belt that when spinning, it has gain room to vibrate at unhealthy levels, but only at times when the engine is churning at particular RPMs.

I've consulted several books (thank you, Haynes) and two mechanics (I cannot afford the formal investigation they wanted to perform) but mentioned it's likely the belts.

What I'm asking is if what I've described sounds about right, sounds way off, and/or if anyone has experience with what I may be experiencing. My intention to replace the belts, one by one, starting with the timing belt.

 

You can easily see if it the belts... or a pulley, may be misaligned: the bushings do go bad and cause may be "wobble".

However, what you describe does not sound like belts at all... why would it change as the car warms up? Better yet, it doesn't happen in reverse, only in drive? This eliminates belts as the culprit. I'd not even bother with the timing belt...

Books won't help you in this case: you need a competent Volvo person to hear it and tell you what's going on.

 

I AGREE WITH LEV....A BELT CAN BE SEEN LOOSE BUT NOT YOUR PROBLEM...

I had a wobble that was due to lack of fuel delivery....intank pump was bad...87 WAGON...

I had a wobble on my 79 242 Manual Trans... and it stop after I replaced the O2 sensor....idled much better...specially when I would go from stand to first gear....chocking itself and shacking...

Just a thought....

How long did you replace the trans fluid?
How long did you due a tune up?

 

check the spark plugs, are all 4 the same or is one darker/lighter than the others?

 

Is the whole engine wobbling or just the belts? If it is just the belts, my guess may be your water pump is worn. The symptoms are a wobbling/grinding type noise at idle that is more noticable when cold. Revving the engine typically quiets it but it will return at idle.

When the engine is cold, pop the hood and have a friend start it. When it is making the sound, check the fan to see if it is wobbling. If so, pull the fan & belts and check the bearings of the water pump (fan bolts to the water pump). If the bearings are loose, time to replace.

 

Lev - thank you very much for the response. I will continue looking for a mechanic who can help me out.

 

analogies - thank you for your response. I will look into both the pump and the O2 sensor. And from what both you and Lev mentioned, I will leave belts alone.

Thank you again.

 

pierce - thank you for the suggestion. I will check those as well.

 

act1292 - thank you for the advice.

It sounds like I have a list of areas to look into, in no particular order:
bearings, bushings, and pulleys
O2 sensor
fuel pump
spark plugs
water pump

I will start all of that with having a friend start the car cold while I observe. I'll also shoot a video during this process, and see if posting it works. Might be useful.

 

A "wobble" is probably a misfire... Many describe misfire in all sorts of creative ways: shaking, dancing, bumping, grinding... Look for a misfire first!

 

hence my suggestion to check the spark plugs, if one cylinder is consistently misfiring, it should be evident.