Check engine light comes on - scan says fuel to lean

I recently took a day and changed sparkplugs, fuel filter, and flushed radiator on my 2000 Toyotya Sienna with 74K miles. Getting to back sparkplugs required my(according to Chilton’s/Haynes manual) to take off upper intake plenum, throttle body control, and all the duct work leading to air filter. Big job, but went ok…so I thought. Van ran great but check engine light came on after about 25 miles. Scan says fuel to lean. Cleared code 25 miles later comes on again. What did I do and how do I fix??? Any suggestions welcome. Will that hurt anything? Van runs good!

A vacuum leak seems like the most likely problem. If you are lucky, you left a hose off or loose. If not, maybe he plenum or TB is not attached properly.

I should have added, any vacuum leak downstream of sensor that measures air intake is big trouble.

I agree with you BandB, about a vacuum leak causing this. Something wasn’t put back correctly and an intake air leak has occured after the MAF sensor. The O2 sensor in the exhaust is detecting the trouble.

When replacing the intake plenum, it’s difficult to not get a wire, or something, caught under the plenum. Did you use sealant on the mating surfaces when you put the plenum on? // On some engines, which sit sideways, different ways to reach the back spark plugs can be used. On one car, I found it easier to remove the alternator, and its bracket, to reach around to the spark plugs. On another car, I had to take off the radiator side engine mount to pull the engine forward 3 to 4 inches, to reach the back plugs. // Sometimes, even with the right pliers and a twist, the spark plug boots won’t come off. Then, since one is changing the spark plugs anyway, use a large screw driver, or pry bar, to BREAK the porcelain part of the spark plug off.