93 Accord LX Wagon automatic, 154,000 miles. Daughters just brought it home from school. Idle vibration follows engine speed (1 per rev?) bad enough to make the steering wheel resonate, a lot worse than my 93 EX coupe auto. Smooths out considerably above 1100 rpm. Vibration is noticeable even in PARK and NEUTRAL.
- No check engine light, no D4 light, no codes when jumpered
- Compression is good, 185-190 across the board
- Spark plugs, wires, cap, rotor new within the last 2,000 miles
- Warm idle speed steady at about 750 rpm
- Stethoscope says all injectors are working, injector resistance and injector resistor check OK
- All cylinders firing (pulling each plug wire results in VERY rough idle)
- Rear engine mount solenoid and vacuum unit working correctly, but there doesn't seem to be much difference when I disable it.
- Haven't checked fuel pressure yet (need a set of sealing washers), but this would affect all cylinders equally.

Questions:
Can anyone suggest a method to determine the frequency of the vibration? I have an oscilliscope, but not an accelerometer.
If 1 per rev, maybe one of the balance shafts is off a tooth? I guess I can pull the timing cover and check the balance shaft alignment marks.
If every other rev, maybe an injector screen is plugged and not delivering all the fuel it should (and is masked better at higher speed/load)? I'll get a set of seals, pull the injectors, and check the screens.

Any suggestions on how to verify functionality of the rear mount; if it provinding any damping at all? Whether the fluid is still inside? I'd hate to change this without knowing it really is bad.

 

what kind of plugs are you using? ngk is best. the set timing might be off. undo the computer or bridge it and check the timing. sounds like it wouldnt hurt to clean the air control valve and tb too. i'd start there before taking off the timing belt.

 

Stock NGK plugs. Timing was set over Christmas break with valve job. I think it vibrated then, but I had bigger issues to deal with at the time, and they complained about it on the trip home. Air control and TB would affect all cylinders equally, wouldn't they? Idle speed is very consistent at 750 rpm, no hunting or up/down, it's just that the engine vibrates. I wasn't going to take off the timing belt, just the lower cover to check the timing marks on the balance shaft pulleys. If I find an adjustable strobe light, I should be able to figure out the vibration frequency.

 

my engine vibrates slightly too, let me know what it is when you figure it out.

 

Balance shaft timing is OK (reset it, but I had it on TDC #1 exhaust, then redid it at TDC #1 compression). Doesn't appear to have improved any. Thought of a strobe light to determine vibration frequency, now I just need to find one. Injector seals should be available tomorrow.

 

Checked ignition timing last night, about 14 degrees BTDC. Tweaked it up to about 16. Found a slight leak from #3 injector this morning when I started it (upper o-ring). Seemed to run a little smoother during the day, a little better at idle, smoothed out at 1000 instead of 1100 and seemed quieter in normal driving range (did find one of the air intake tubes pulled partially out of the filter box). Pulled the injectors this evening, all screens clean. Reinstalled with new seals and new filter while I had the system depressurized. Fuel pressure with vacuum off about 43 psig. Little running tonight didn't seem any different than during the day, still more vibration than the EX. I'll see what it does going to work tomorrow.

 

As stated above, better than it was when I started, but still more vibration than my 93 EX auto. Haven't found a strobe light yet. Tried a timing light on the coil wire (should yield pulses 2x engine speed), showed a little variation in timing between cylinders (+/- about 1 degree), but tough to tell vibration frequency.

Any other suggestions for what I think is a 1/rev (or 1 per 2 rev) vibration of engine?