In a effort to make my '88 740 dependable enough for my daughter to use (she lives about 200 miles away), I've replaced a number of components. However, I've been unable to eliminate a vibration while the car is at idle, auto trans in drive, and foot on the brake. The vibration shakes the whole car, but disappears when the transmission is shifted to park or neutral or when you increase the engine speed by slightly depressing the accelerator. When you put the car in gear, the engine speed drops about 200 rpm's (the tach doesn't read accurately so I can't tell exactly what the engine speed is, only that it drops). I've replaced the cap & rotor, spark plugs (gapped at .028), intake manifold gasget, amm to throttle body bellows, vacuum hoses and cleaned the IAC and flame trap, checked the timing (12 degrees BTDC). Plug wires were new within the past 2 years. Any help to diagnose and cure this vibration would be appreciated.
Marlin

You mentioned that you cleaned the IAC but it's also a good idea to test it to see if it's operating properly. They can be clean but still not open all the way. Connect the pos battery terminal to the middle pin and ground the outer pins one at a time. It's a torguey little motor and the valve should flip back a forth quickly. Maybe remove the throttle body and also give it a good cleaning. How's your air filter ???

Replace your engine mounts... about $30 and 2 hours of your time.

I replaced these with Volvo parts in 1998 at 100,000 miles and it now has 244,000 on the clock. Do these compress? Will the oil pan be resting on the crossmember?
Marlin

The passenger side mount tends to go bad first; maybe because it gets oil spilled on it if it isn't covered when the oil filter gets changed. Maybe that's why the oil filter tends to be the first thing to hit the cross member as the engine starts to tilt to the right. Spin your oil filter 1/2 turn and see if there is evidence that it's been touching. Also, do your motor mounts have metal straps on them and are the straps broken? I don't think the straps are there for anything but to warn you that your mount is bad.

I think after 144K, it is reasonable to suspect the mounts.
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Andy in St. Paul. '89 244 160K mi, '91 745 209K, '91 745 213K

No, engine mounts should not compress at all. Volvo mounts are intentionally short-lived - a safety feature. You should probably check your tranny mount as well.
No, the oil pan should NOT be touching the crossmember!
Do a search thru the FAQs on this site for 'advice' on changing the mounts easily.

Happy Motoring.

Mike H.
89 740 B230F M47

If your engine mounts are bad, your oil filter will be perilously close to (or touching!) the cross member. You also have a transmission mount which could be bad.
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Andy in St. Paul. '89 244 160K mi, '91 745 209K, '91 745 213K