Lower mileage after cleaning throttle body and MAF sensor

What did the dealer do to your car?

You won't get any better mileage by cleaning the throttle body and I have never seen that mentioned here.

Take the air cleaner box off and check all the hoses are connected. Take the big hose off the back of the tb and spray the cleaner through that port. That's the one that gets dirty as the big hose is the pvc hose. Check for free play with the butterfly by turning the springed end. Lubricate the springed end. I know the maf is plugged in because if it wasn't it would throw an instant dtc.

Then when you put the air box assy back on make sure the throat clamp underneath the air box is tight also.

 

The dealer didn't do anything- he decided to do the job himself..

... day late and a dollar short..

 

1. Please explain your exact procedure used to clean the throttle body and mass air flow sensor.
2. In general, less is more when doing these cleaning procedures. This means you do not need to use 1/2 can of throttle body cleaning fluid and drown the intake manifold in cleaning liquid, to achieve a good result. The Toyota recommended procedure is to spray some cleaning fluid on a clean cloth and use that to scrub dirt off the throttle body interior and throttle plate, rotating the throttle plate shaft to gain access to the underside of the throttle plate. This avoids having dirty cleaning fluid laden with dirt getting into the throttle body motor shaft and binding the motor. Obviously the air cleaner housing has to be removed for access.
3. The mass air flow sensor is cleaned by removing it from the air cleaner housing, and spraying the sensor bulb and bare wires with MAF cleaner. Do not touch any of those cleaned parts and make sure you have a good seal when reinstalling the sensor in the air cleaner housing.
4. It is not reasonable to expect improved mpg by performing those cleaning procedures.
5. The point of doing the throttle body cleaning procedure is to avoid engine no-start issues (DTC P3191 for example) which can happen if the throttle plate binds up.
6. The point of doing the MAF sensor cleaning is to improve the engine ECU's ability to manage fuel delivery to the engine, and avoid a DTC being logged (such as DTC P0171, P0172, or one of the P010x codes.) That might result in a marginal mpg improvement but that should not be the primary motivator behind that cleaning activity.
7. Make sure the wiring harness connector to the MAF sensor is properly engaged and locked.

 

You killed the MAF.

 

1. It is not helpful for any debris to be allowed into the intake manifold. The concern is that the paper may stick to the edge of a valve, carbonize, and prevent the valve from sealing properly.
2. What did the MAF sensor bulb and wires look like, after they were cleaned?
3. At this point, if your car is not logging any warning lights, you should just drive it and perhaps the mpg will improve over time.

 

I feel another guess coming on. The additional cleaning fluid in the bottom of the intake manifold has dissolved the oily residue that collects there and when ingested into the engine has temporarily fouled the plugs. It is more likely that the 12V battery has decided to give up the ghost in conjunction with this procedure. Working on your car with the windows down and your favorite radio station playing for 30 minutes or more (guessing here) might have been all it took. Excessive engine run times and a corresponding drop in mpg are a good indicator of a weak 12V auxiliary battery. Run this check and if the second voltage value is much below 12.0V you probably need a new battery.

 

A reasonable hypothesis, and the OP can prove or disprove this by removing the iridium spark plugs for inspection.

 

Have you actually measured the 12V battery voltage? If not, you might be unpleasantly surprised: Prius won't run. | PriusChat
See posts 5 - 7.

 

I am reporting the exact same experience; I cleaned the MAF and TB yesterday using the CRC spray cans (MAF cleaner for MAF and TB cleaner for TB) and my Prius (2007 with 91K) doesn't turn ICE off as quickly as before. I didn't use paper to clean, I used a clean cloth to clean the TB. I did liberally spray the TB cleaner on the butterfly and underneath; no, I did not spray more than 5 or 6 times.

 

Ecu just needs to learn characteristics of changed throttle body. If it was dirty enough it may not even shut down engine at first. It learns it bit faster if you disconnect 12v battery for 10min to reset ecu. Or you can just drive it and it will eventually learn it.

 

I re-checked and re-tightened all the screws that I had removed/loosened for the job, found one screw that was loose, oops. Now, my Prius is back to normal. Thank you!

Stone

 

What about the non related MPG decrease as winter approaches? OP doesn't have a location listed.