1998 Toyota Camry Intermittent misfiring

Hi Guys,

Sometimes, usually after a long drive and a lot of stop start (e.G. Peak hour drive to work) my '98 Toyota Camry V6 (automatic transmission) will start misfiring severely and really chugs when idling. When accelerating it's pretty smooth but if I'm coasting with accelerator slightly depressed it will misfire and be jerky/rough. The problem is very hard to reproduce due to the randomness of it, probably happens 1 out of every 5 drives in to work (approx 30km drive in peak hour). It will ALWAYS happen when I try to tow a heavy load (e.G. Trailer load of sand) and I was doing this when it first started happening.

When I idle, the tachometer needle will swing from 200 to 800 revs alternating probably every second or so. If I leave it for 30 seconds it will stabilize at around 400-600 revs and will chug. The car normally idles around 800-1000.

Engine temps are normal.

If I turn the car off and let it rest for 5 minutes or so and attempt to start it up, it will struggle and crank over a few more times than normal but when it starts it's fine and back to normal.

I've changed over plug leads to no avail, I've assumed plugs are OK because if it was a plug problem it would always happen.

Any ideas anyone?

Thanks in advance.

Regards,

Daniel