Toyota Repair: Injectors staying on, toyota camry vienta, cattle grid

Question
QUESTION: Hi Ted
I have a 1996 Toyota Camry Vienta v6 with 160,000km.  It has developed an intermittant miss that is sometimes very light, sometimes not there at all and sometimes is so bad it feels like I'm driving over a cattle grid!.  When the car misses it puffs white / blue smoke that smells heavily of fuel and a little of oil!  When not missing, the engine is purr-fect & produces no smoke.  I have had a mechanic inspect and also taken it to Toyota.  We replaced leads, plugs and the distributor rotor (which had a tiny burn hole underneath it where it had been shorting out).   The problem persists although it can dissappear for 3 days (300 + Kms) at a time.   My mechanic had a similar experience recently and suggests the ECU has a problem.  He lent me a little light to plug into the injector wires & this reveals that some injectors are being held open at those times when the engine is missing.  I noticed when I had my head under the bonnet and the engine stalled that the problematic injectors were erratically buzzing while the ignition was left on.  Toyota elected to ignore the electronic type problem and suggest AUD$2,500 to remove & recondition cylinder heads due to worn valve guides causing valves to stick open.
I look forward to your comments, Kind regards. Michel


ANSWER: I don't agree with the valve problem diagnosis,it could be a problem with the ECM or a loose computer ground point, is there a check engine light on?

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QUESTION: Thanks Ted.
No, there is never a check engine light on.  I have tried driving after unplugging the most troublesome injector and find that the smoke clears up quickly.   There is then the obvious miss from not firing on that cylinder and the occassional further miss from the other injector playing up.   Can you suggest where to check for a faulty ground point please.

Answer
The computer ground points are usually located behind the left and right side kick panels, the wires are white/black, there are several connections on each ground point, you may also try to locate the computer, normally located behind the glove box, and remove and check the connectors, check for any corrosion on the connectors, if a DVOM is available check all the computer wires that are brown/black with the ohm meter to body ground, all these wires should be directly grounded to the body(negative earth to you in AU).