As far as the growling noise, i had a similar problem. It would make noises when stopped in neutral and also make noises when you would let off the gas at high rpms (letting the transmission push the engine). The Honda D series transmission have a common problem of the input shaft bearing going out because the oil fill level is below this bearing. I took mine apart to find the bearing on both sides of the input shaft were shredded. Also replace the seal for the input shaft.
If you take the transmission off to do something like replace the clutch, its fairly clear if its the input shaft because there will be tons of slop in the shaft. also make sure the throwout and pilot bearing are smooth while its apart.
On my '90 Si, the pilot bearing is a press-fit into the flywheel.
When I first bought it, it growled loudly on decel in every gear. I pulled the transmission out and found the pilot bearing ate itself up, and the hole for the pilot bearing had been worn larger so a new pilot bearing would not press-fit. When this happened, it took out the input shaft bearing. It was cheaper to buy a used transmission than to repair it. That was 7000 miles ago and everything is still ok.
Now I need to see why the previous owner duct-taped the clutch pedal.
An exhaust leak ie cracked manifold wreaks havoc on a VX because it throws off the O2 sensor. That may have been 60% of your problem right there.
Even if your O2 sensor is good you should periodically clean off the carbon build up. The best way is to heat it up with a torch and then blow it out with compressed air. Never use any kind of solvent on it.
repairs made since: new o2, tranny bearings fixed, tranny seal fixed, bought a tach to chk rpms
mpg this pump @ 30mpg better than my 26.. but still having horrible mileage compared to everyone else... will try next..
will get a new exhaust manifold this week (they are expensive anywhere to get a cheaper one than $250) , and also tires and alignment done. anything else that could be going bad? maybe my cat? that would effect my mpg... i would be happy for just 40mpg.. even thou i see people breaking past 50...
Can you have you exhaust manifold welded? I had a cracked manifold on my 3000 gt and only paid 20 bucks to have it done. I had to remove and reinstall it but i saved the manifold and is good to go. check around at some muffler shops.