Engine runs rough when cold. No check engine light.

A couple weeks ago my truck started running rough when it was cold, didnt think much of it because it wasnt too bad. About 50-60 miles later it has become worse, almost where the truck will barely take off. It gets a lot better after the truck warms up, almost running perfect but still a little miss in the engine. I wasnt worried thinking it would throw some codes and I can start from there but none have come up, no check engine light. I did hook up my Obd reader to see if there were any codes but none came up. Truck has 217,000 and T belt was changed @ 198,000.

I pulled all plugs they look like they are all firing no gunk build up. The gap was around .40 so regapped them to .31 as it states in the owners manual. Put 15 gallons of fresh premium gas, cleaned the MAF sensor, checked all vacuum lines and cleaned the throttle body but has made no difference.
Before I start throwing parts at this, fuel filter, coil packs etc... I was wondering if anyone else had a similiar problem and point me in the right direction. I do appreciate all the help and advice.

 

If the plugs were worn to. 040 my first thought is how many miles are on them, what brand and type.

 

Run some fuel injector cleaner too

 

Replace the plugs and run a can of Seafoam p/n SS14 through it.

 

Not sure how many miles are on the plugs but Im going to change the fuel filter today, if the problem is still there I will change out plugs.
Thanks

I usaully run Top tier gas in it so I would think that the injectors would be clean. I guess it wont hurt to run a can of BG44k through the system.

I thought about the seafoam but I heard it was bad for your catalytic converters.

 

I've been using SeaFoam in my oil & gas since the mid 90's, it has never caused a problem - it only solves / prevents problems.

 

I never have used seafoam but I have read that it can clog up your cats with all of the carbon and gunk that the Seafoam cleans off. Thats what I have read but never tried the stuff myself. I might try it if the filter and plug change doesnt work out.

 

Sounds like you've done all the obvious stuff so I would move on to the not so obvious.

As cheap/easy as they are to replace, I would do the plugs and fuel filter. I'd also test/check your charging system (battery cable tighness/cleanliness and alternator). I had some weird issues with mine doing a rough cold start and actually dying and once I replaced the negative battery cable, it runs like a top. The next item on my list was going to be fuel pump but mine has been great ever since. Here are the threads of me chasing it down:

https://www.tundras.com/threads/slight-hesitation-while-stopped-sometimes-dies-when-starts.54963/
https://www.tundras.com/threads/occasional-crank-no-start.57039/

 

Thanks, I checked the negative cable and grounds and all looks good. My alternator was charging at 13 something volts so it's fine. Replaced the fuel filter, same problem but now she finally threw a code. Shows misfire on #6 so I need to do a little homework and see how to check that coil with my multimeter. Oh and might as well get new plugs.

 

These coils are known for cracking. Again, as as easy as they are to work on, swap #6 coil to a different cylinder and see if it misfire follows. Also inspect them.

 

Pulled out #6 (on left) which the code indicated misfire and # 4 (right), defintely a discoloration on the #6 boot and plug. I see I can buy a replacement boot for $7.00. Would just a bad boot cause a misfire, or should I just buy a brand new oem coil from the dealership for $90.00?

 

Replace the plugs and swap the #6 coil to cylinder #4. If the misfire follows, you know you have a coil problem.

Are there any cracks along the coil? Here is an example:

 

I read through your thread awesome to see you got your truck up and running.
The coil looked good no cracks just the boot had discoloration. As you mentioned I swapped the coil to #4 and for some reason it's finally throwing me codes. Now it shows misfire on #4. I just went ahead and ordered a new Denso coil and plug, should be here tomorrow. Hopefully this fixes the missfire. . Out of curiosity I'm going to take off the new boot and put it on the old coil just to see if that would have fixed the problem.

 

Sounds like you are on the right track!

Wild guess but maybe the boot discoloration is from the coil arcing through it and causing it to get hot/light colored.

 

You could be right. I just switched over boots on the coils and it still pulls up misfire on #4, so I answered my own question lol. The boot had nothing to do with it looks like a bad coil.
Just got the new coil in and she runs like she used to.
Appreciate the help