Engine rides rough for first few minutes

My 1998 Sienna (139k) rides rather rough for the first ten minutes after sitting for ten hours or more. The engine jerks (misfires I believe), won’t accelerate easily, etc… The problem is more pronounced in colder weather, but it happens in warm weather too. It drives fine after warming up. I’ve replaced plugs and wires to no avail. The problem has gotten worse over the past year.

When was the last time you replaced the fuel filter? Chances are, the filter is clogged up and restricting fuel flow. The van needs more fuel when started cold than when warmed up, but if the fuel system cannot meet up with demand, you’ll get those symptoms.

Also, the CEL will not go on because the oxygen sensors are not read until the van is warmed up. Oxygen sensors don’t give good readings until warmed up.

First start with the free stuff. That is stuff that should have been done and may not have been done like the fuel filter, spark plugs and wires. There are other things, but check that stuff out first. If it is due or past do, do the maintenance first and see what happens.

That’s right: the CEL hasn’t come on despite the rough riding. I’ll replace the fuel filter and let you know. Thanks!