98 Camry V6 Misfiring (only sometimes)

[pinchedloaf]

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 (1MZ-FE engine, 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

[AlmightyCamry777]

some things i would check

-replace spark plugs. They can misfire under load and be fine at other times.
-replace fuel filter...there's no practical way to check it, you have to go by the last time you replaced it to know when to change it.
-check air filter, can you see the sun through it? If not, replace it.
-does this engine have a distributor cap and rotor? If so, remove the cap and inspect inside it and on the rotor for burning and pitting. If found, replace cap and rotor - i had a truck at work that would barely run, we replaced the cap and rotor and this fixed it.

-Clean inside the throttle body and throttle butterfly with carb cleaner or sea foam spray. This area gets very dirty in Camry engines and needs to be cleaned about every 30,000 miles.

[73sport]

No CEL as of yet? Is that idling in gear?

I can say I went down a path very much like this only w/ 6 coil packs not 3. Key words are missing under load says the spark is not there.

See if you can find an auto store that will let you install the coil packs for a test drive, but you want the clause of "return if it doesn't help" in there.

Everything you say implies its missing under load which as Almighty said, can be from bad plugs. Fine at idle, fine at cruise, but when the engine demand is high the ignition system is put to the test and it fails.

Do plugs if no change, do the coils. Confim no new cel codes and get the freeze frame data if possible.

Here's a some reading for you: 2, 4, 6, All lean, Why? Need Help!