TB Clean + mpg drop

I took off my throttle body and cleaned it along with the MAFS and the intake manifold at 121k miles. Looked real bad, but now it is shiny. I tried to get all the gunk on the rag, but some of the carbon on the intake manifold obviously went through the engine. I started and ran the truck for 30 minutes (driving). It seemed to make white smoke for about 10-15 minutes. The next tank of gas was great. I got 25mpg city... which i've never even got on the highway before. I was so excited, until the last 2 days.

1-2 gas tanks later I'm getting 15mpg city (110miles on 7.5 gallons). My thought is I either plugged the pre-cat O2 sensor or the cat itself or the MAFS went bad (doubt this), or I somehow hurt the piston heads/rings (but I don't feel a power loss). The truck also idles at 600-650rpms instead of 700-750 rpms. There is no check engine light.

Tests? Thoughts? Help?

I'm considering:
beating my head against a wall pulling out a rusty O2 sensor for cleaning/replacement
chopping off the exhaust before the cat & replacing with new O2/resonator/muffler & no cat (I have an emissions test from October & I hope to move to a part of Texas in the summer where emissions testing isn't required)
living with it
going on a long drive (leaving the truck burning in 2nd gear)

 

Bump,
I would check the maf but I don't have a clue

Good Luck!

 

Yah I'm really betting it is the O2 or the CAT. I just don't understand how a dirty O2 after the engine would lead to a "rich" setting. Because logically when something is dirty it makes sense it reads less O2 in the exhaust than O2 actually present equaling a lean mixture. But I guess somehow the deposits could increase sensor voltage and give a false O2 high.

Also... maybe my short city driving hasn't been long enough to heat up the O2 and give a CEL. But then idk why the O2 readings would even matter.

 

Are you throwing a CEL? If not everything mentioned here seems completely normal to me...

Make sure you fully attached your MAF connector. Running a straight pipe with no cat/resonator? Could be affecting your back-pressure.

 

fouled plugs?

 

Should I do anything besides take them out and spray them with cleaner? Like should I turn the car on an run a little bit of TB Cleaner through the engine to make sure I got everything? Because last time I just did it with the car off.

 

well now cleaning the spark plugs these days esp. with spray cleaner is new to me.. now back when i was 16 and you had to tune a car every 12,000 miles my grandfather had a plug cleaner he got at sears. it sand blasted them. not up on all the info on the 4 banger, but i assume you should replace them with the standard toyota plug (nothing fancy) evey 30,000 miles or so. in the old days they would foul quick, now they just wear out..
the O2s sensor can be strange... i think u have 2 also, but the one near the motor does most of the "sensing" the other is a back up, and when they start to go your engine performance can slip till you get the CEL and have you checked your PVC valve?

 

If you have 2 O2 sensors on a single exhaust manifold (4 banger not a V engine) then the first determines the correct AFR and the second controls the CEL for the Catalytic converter being bad. no "backup" sensors

 

I haven't check the pvc valve because idk where it is lol... I know there are tons of pictures that show it, but I still don't see it on my truck. It's like the one thing I'm not familiar with.

Also, my plugs only have 5k miles on them so cleaning & brushing might work. I haven't looked at them yet though.

So everyone here agrees the first O2 sensor before the cat won't throw a CEL?

 

That one can throw a CEL if readings are out of normal, but will not throw a CAT code

 

dont know if i missed it but what kind of plugs did you use?

 

Most use stock Toyota plugs. you can search for Chris4x4's truth about spark plugs too

EDIT:

http://www.tacomaworld.com/forum/technical-chat/152726-truth-about-spark-plugs.html

 

no, no, thats good, long time ago before i knew better I was gun ho about the latest and most expensive plugs...
I remember these two threads, maybe the one will help before you have to spend any more money. I understand its a pain, but there is a answer to this.