2000 T4R misfire on startup

[fotorunner]

2000 4R with 307k. On start up it will run rough for anywhere from 30 sec to 1 min. Then it seems to level out and run normally. This is also intermittent, doesn't happen on every start up. Replaced timing belt recently and for a few weeks after that it didn't have that issue.

On the highway it seems to accelerate normally with no missing.

Had it at a dealership yesterday and they checked for codes and there was nothing.
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[Paul cammack]

What kind of coils are you using? I had some performance coils and was having this happen maybe 1-2 times per month and finally pinned it on one of the coil packs. Swapped out all 6 for Bosch coils and have had no misses since.

 

[JoeT4R]

Can you elaborate a bit on how its running rough?

 

[BretMann]

I had similar symptoms and it turned out to be a failing plug wire where it was corroding where it connects to the plug. As the engine would go from cold to warm the connection would change. I changed all the wires and then the coils too just to eliminate future issues - while I was in there, and that fixed it.

 

[fotorunner]

Thanks for the replies.

This has the original coils on it.

Intermittently at start it will miss and smells a little gassy. This usually lasts until it comes off of fast idle. Then it seems to run fine.

Thanks, I need to check when we replaced the wires last.

 

[JWaldz]

[MENTION=8550]fotorunner[/MENTION] run a combustion leak tester (block tester) just to eliminate onset head gasket failure.
Pretty easy to use and I believe you can rent them from an automotive store.
FWIW, it could still be very preliminary head gasket failure and not test positive for a combustion leak.

Rough startup can be a multitude a things, and without it throwing a code, you're just going to have to try multiple things, or wait for it to eventually throw a code.

From experience, my head gasket failed on Cylinder #3 and had very minor issues in the beginning, but was showing some signs of a problem. It didn't throw an actual code for the cylinder misfire until they started getting more frequent, about 3-4 times a week, and usually only after sitting for the night. Otherwise, aside from some spiky coolant temps under heavy load, it drove fine. It took around a couple years of every day driving before it finally gave out.

 

[mtbtim]

You most likely either have a bad head gasket or cracked head. The reason why it runs rough after a cold start is coolant that has pooled on top of one of the pistons is burning off and fouling out the spark plug. Once the coolant burns off, the cylinder fires correctly and the misfire disappears.

You should do a leak-down test of each cylinder and you'll most likely figure out your issue. My guess is one of your heads has cracked. It's very common.

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[JWaldz]

You most likely either have a bad head gasket or cracked head. The reason why it runs rough after a cold start is coolant that has pooled on top of one of the pistons is burning off and fouling out the spark plug. Once the coolant burns off, the cylinder fires correctly and the misfire disappears.

You should do a leak-down test of each cylinder and you'll most likely figure out your issue. My guess is one of your heads has cracked. It's very common.

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Cylinder #3 for me :sad:

 

[Daryl Elmore]

You most likely either have a bad head gasket or cracked head. The reason why it runs rough after a cold start is coolant that has pooled on top of one of the pistons is burning off and fouling out the spark plug. Once the coolant burns off, the cylinder fires correctly and the misfire disappears.

You should do a leak-down test of each cylinder and you'll most likely figure out your issue. My guess is one of your heads has cracked. It's very common.

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Unfortunately what Timmy said. I had the same thing, rough idol at cold start for a very short period of time, it also blew just a little smoke, once warmed up everything was fine. I had w small cracks between the valves in #4. once warmed up, the metal expanded and sealed the cracks, when cold it allowed coolant to seep into the cylinder.