Cleaned MAF, now ICE runs more often (doesn't shut off easily)

Before Bisco gets to this thread, how many miles on your car?

 

Dan
I did mine for the first time a few days ago and I noticed the exact same thing. The only thing I've come up with is that coincidentally it was a cool morning the day after I cleaned mine and my heater was running and I didn't realize it (it was 68 outside and auto ac was set at 73). From my searching it looks like the ICE will continue to run at a stop if the heater is on. I've made a point of turning the heat/ac OFF before doing stop and go's to see if things went back to normal and I think that they have. I to would like to know if anybody else has experienced this.

My car has 213,000 miles.

 

Disconnect the 12V battery for a few minutes and then reconnect. That solved this for me after I cleaned my TB and had the same issue.

 

there's an app for that.

 

Roll the window about half way down, then roll up completely and hold for 2 seconds. That should fix it

 

I have cleaned my TB and removed and cleaned my MAF twice now and never had this problem. I can usually count on a tenth or two of a MPG improvement, which varies by season. The idle quality never changes, smooth as silk, no matter how dirty the manifold side of the TB gets. I have also removed the strange liquid that accumulates in the bottom of the intake manifold. It is somewhat oily but not pure oil. I think there is some "splatter" back into the manifold due to delays in the intake valve closing under certain conditions. Might just be coincidental. Something else that will cause excessive ICE run time is a weak 12V aux battery. You might want to check that. Funny how other parts of the car get the hint that you are in a maintenance mood and start acting up.

 

This is correct, that liquid is partially unburnt gasoline which comes out of the intake valves. This is because the Prius engine uses the Atkinson cycle where the intake valves remain open part of the way during the compression stroke. Some of the liquid may be engine oil and condensed crankcase vapors which get deposited via the PCV hoses.

 

Out of interest, just how long was it taking for the engine cut out after you came to a complete stop? Normal is about 7 to 10 seconds, though every now and then I experience a longer delay (rarely, but sometimes up to about 17 seconds) in particularly hot humid rainy conditions.

 

When you say disconnect, do you just unplug the connector to the 12v battery or you disconnected the ground wire?

Thanks

 

Easier to just loosen the negative terminal clamp on the battery, remove, count to five, and replace. I try and stay away from the positive side of the battery with any tools. Alternately you could remove the negative cable mount on the inside trunk wall. I did that once and it is pretty sparky putting it back on. Make sure that connection is clean and tight though.

 

Thanks. You lost me at "sparky" lol. I'll just do the traditional way -- loosen the negative.

 

It is much easier to disconnect the negative cable where it bolts to the body, vs. at the battery itself.

 

So I disconnected the negative cable this morning. It was hard to reach the terminal so I disconnected where it connects to the body like Patrick mentioned. I was surprised to see some sparks.

Anyway, that resets the tripometer, mpg calc, windows one touch, etc... It was 34 F outside this morning but I drove it with the heat off to make sure. I didn't see any difference The ICE shuts down at some stops, but not always. There was one time I came to a red light (at the beginning of it) and the ICE was on the entire time. I don't know... car runs, mpg is around 49 mpg (used to be 52 mpg), no fault code from the OBD II. I drove a good 50 miles since I disconnected the battery. It's just weird to me.

 

How long have you owned this car?
Have you driven the car in cold winter weather before?
What exactly is weird - the fact that the engine continues to run at a stop, or some other issue?
If you are still getting 49 mpg in an environment where the ambient air temp is ~40 degrees F or lower, that seems pretty good to me.

 

It's an 07 Prius with 123k. I bought it used a few months ago. This will be my first winter with it. I think it's weird that it sat at the stop light for over many seconds (10-30??) without the ICE shutting down. The night before, the ICE did not shut down at all for a good 15 minutes in park (but that was before disconnecting the battery). The mpg dropped from 52 to 49 literally overnight after I cleaned the throttle body.

But I supposed you're correct. 49 mpg isn't exactly bad. And, it's my first winter with it so wasn't sure what to expect. The sudden change after cleaning the throttle body bothered me a bit.

 

Did you disconnect the 12V battery at the same time that the throttle body was cleaned?

I would not expect that throttle body cleaning would make fuel economy worse. It is possible that disconnecting the 12V battery may make reported fuel economy worse, for a while.

Was the engine fully warmed up, and the cabin heater on at the time that the car was stopped while the engine continued to run? If so, next time this happens, turn off the cabin heater and defroster functions and see if the problem persists.

Once the engine is warmed up, it should stop when the car is at a stop unless you have the cabin heater on and the engine needs to continue to run to heat up the engine coolant used to heat the cabin heater core.

 

Nope to all. That's why I thought it's weird. I've done this many times on my Corolla and everything was fine. My inexperience with the Prius making me doubt many things. Well, the car runs with no fault codes being thrown and 49 mpg is not bad (especially since you stated that it's quite normal around winter time), so I guess I should just wait it out and stop worrying.

 

Wait and drive for a couple tanks and it'll improve. The car needs to relearn how to be most efficient