Car Questions

Notifications
Clear all

Car Misfires When Cold Started

   RSS

0
Topic starter

 Hey Scotty. I have a 155000 mile Toyota Corolla 2004. The car runs fine, but it's rough idling and having misfires only when cold started. After the car gets warmed up, the problem stops. It has new OEM spark plugs and coils. Any idea what could be wrong? I recently added Royal Purple to the gas tank, don't know if it could be that. I have codes p0300, p0301, p0302, p0303, and p0304 on my scanner.

8 Answers
3

Could be a lot of things on a 19-year-old car. What do your fuel trims look like?

STFT stays around -2.0 and 5.0 but most of the time it's at 0
LTFT stays around 5.0 and 8.0 but most of the time it's at 7-7.5.

The LTFT indicates that extra fuel is being added by the computer, possibly due to a vacuum leak.

3

Please check the FAQ

1

Why did you add Royal Purple gas treatment in the first place?  Did all these misfire codes occur after the addition or before?

2 or three days after the addition. I added it because as it is an old car, I thought it might help the fuel system. Also, I was getting (and still am getting after adding the fluid and resetting the CEL) other codes that I thought this could fix: p0420, p0442, p0446.

1

It appears from these codes that you have a malfunction, leaks, valves, in the EVAP system.  Fix those first.  They can and probably are contributing to the misfire codes you said you had.  I would not be wasting any more money putting expensive and useless additives in your gas tank.

1

Did you check the gap before you installed them 

They sometimes come out  bad from the factory 

 

Did not check gap. Is it safe to regap these?

1
Posted by: @henryej7

Is it safe to regap these?

Scotty answers this in one of today's videos:

(The takeaway is don't try to regap iridium spark plugs. Other types would be OK.)

Thanks, I watched it earlier today and when he said not to regap them I was thankful I hadn't tried to, haha.

0
Topic starter

 My Toyota Corolla 2004 has 156,000 miles on it. At the time I bought it when it was at 150,000, I replaced the spark plugs. All the old ones looked awful, they were rusty on the threads and electrodes. I'm getting some missfire codes every once in a while. Could the new spark plugs have gone bad after 6000 miles from rust spreading to them? Should I have used or done something before installing the new plugs to avoid them from getting rusted (such as using anti-seize)? I have not checked the condition of the new ones after 6000 miles of use. Should I inspect them?

0
Posted by: @henryej7

Is it safe to regap these?

why wouldn't it be? Just curious.

I don't know haha. I've heard some spark plugs are not supposed to be touched. No regaps, no anti-seize none of that. What I mean is, will I break something by regapping them?

that's because they come pre-gapped. I don't see what could break.

Ok, I'll take a look at them and see if there's anything interesting going on, measure their gap and all of that. Thanks for the tip.

Share: