Intermittent hesitation in a 2008 Prius

I suggest you obtain the current DTC and if it shows a misfire (DTC P030x where x is 1 to 4) then check the wiring harness connectors to the associated spark igniter and fuel injector.

 

Has the throttle body been thoroughly cleaned?

Are you the one owner and if so was the car ever in a wreck specifically the front end?

And lastly what kind of oil do you use when you change the oil and how often?

 

Thats your problem. The throttle body has never been cleaned. The maf is just a sensor way upstream of anything that can make it dirty but good to clean it once in a while. Any maf issue it will throw a DTC.

The Prius TB like most modern cars gets very sooty and really requires attention every 15-20,000 miles.
Take the air cleaner box off and with a flashlight look down the throat while turning the left spring to open the butterfly. I bet its very dirty and the butterfly edge is badly corroded.

Many posts here of people never cleaning them and require the TB be replaced to the tune of $1500.

 

Fuel induction and or injector service has nothing to do with the throttle body. The throttle body only regulates air not fuel and it is way upstream of the Injectors. I question the shops competency that suggests a fuel service when asked about a throttle body cleaning. BK 44K does nothing to address the throttle body as none of it flows through the TB. Your thinking of a carburetor from 30 years ago.

Like all modern cars the pcv valve output dumps crankcase vapor and blowby directly into the top of the throttle body which is troublesome as crankcase vapor is pretty nasty stuff.

Poor oil maintenance of the engine or the car spending its life on dino oil exacerbates any crankcase vapor contamination intensity.

I suspect your throttle body has never been cleaned in it's long life and if so its surprising the engine is even running. Please do as I suggested in post #5 and see how bad it is.

 

See if the trans fluid smells burnt. I just heard about a gen 2 with similar weird intermittent hesitation except at all speeds. The trans was very low on fluid. Planetary gears were grinding up. Metal chunks came out with the fluid.
This is just a guess but the lugs that bolt down the wires for mg1 or mg2 could be loose. That would cause fluctuating control of mg1 and the computer would probably compensate by changing engine speed.

 

Has anyone, professional or otherwise suggested checking/replacing the in-tank fuel filter? I assume they are designed the same as the Australian deleivered spec cars. I replaced ours at 80,000km in our 2007 that we bought new and I was amazed at how dirty it was already, I cut it open and expanded the paper to look. I noticed an immediate return to more torque/power and smoother running all round. That was at 80k with immaculate service history, genuine oil and filter every 5-7,000 km. I have just bought a second hand 2005 with 220k not going with a bad injector causing misfire and shut down. I have addressed the offending injector but it still has issues particularly when cold, rough, erratic idle and slight misfire across all cylinders. I'm going to pull the fuel filter and replace it plus clean all injectors. This car was serviced twice in 70,000km and it shows. I had to put rings in the engine as the oil rings had become stuck down. I'm tipping it's not getting the fuel it needs cold and runs lean causing misfiring. Coils are ok. Maybe your's is suffering a similar prob?

 

North American Classic and 2G Prius have the fuel filter within the fuel tank and it is necessary to replace the tank if the filter has a problem.

If you have photos showing what your fuel filter looks like, and how you accessed it, pls post.

OP says that there is no hesitation above 50 mph so I doubt the fuel filter is the issue here.

 

It appears to be the same design. I know it sounds counter intuitice that it may perform well under load abd yet exhibit idle issues however I can only share what I observed by experience. Low fuel rail pressure and minimal injector pulse width can show up these issues. WOT conditions increas pulse width and can mask this condition. Its worth exploring when it last had a filter if ever.

 

The filter is in some markets suggested for life unless a problem occurs much like the trans ws fluid. This is simply madness in my opinion. I have replace several and all were dirty at distances of between 80-150,000km. Even if it doesn't address the prob its worth doing imho.

 

It really sounds like the throttle body. The tb is fly by wire no cable so you really can't feel if the butterfly is getting stuck.
Please take pictures of the throttle body bore as I suspect whoever cleaned it did not do a good job. See how free the butterfly is by rotating the end with the spring on it. The tb motor is on the other end of the butterfly and may be gunked up too.

Also be aware this engine uses oil pressure to actuate the variable valve timing. That drive oil has to flow through a very fine serviceable oil filter before it hits the actuator. If the car was not serviced well that filter may be getting clogged and the car will run poorly. It can be found behind a hex head bolt underneath cylinder #1 intake.

How many miles on the car when you bought it and has it been doing this since you bought it?

 

I agree with Edthefox5, regarding the throttle body. The fuel filter in the tank on the US Prius is not changeable "as stated by Patrick" requiring replacement of the fuel tank at $1000 +.

John (Britprius)

 

I doubt it Brit. The same pump and filter assy is used worldwide. It may not be specified as a servicable item in some markets but you may be sure it is the same design. As I say, low demand, ie: narrow pulse width combined with compromised rail pressure can show up as a hesitation that disappears as pulse width increases, effectively masking the problem. Rail pressure often increases with throttle demand with some designs. Yes Ed, quite right, TB is an obvious nil cost elimination and sensible thing to do.

 

Bruce, it is not a case of what pump or filter is in the tank.
The US fuel tank is sealed totally the only way in is to open it it up with a hammer and chisel or large can opener. It does not have an access panel as in most cars. The area outside the bladder to the inside tank wall is monitored for fuel vapor, any leakage gives a DTC.

John (Britprius)

 

So what do you do in the event of a fuel pump failure?

 

For the US gen2 Prius fit a new tank.

John (Britprius)

 

Ok Brit, I can be wrong as I'm human. lol. That has got to suck! With my car it would be a 30 min operation and cost 50 bucks, so that is why I say if you can, do it. They are specified every 80,000km here in the service schedule, but not in all markets. I bet it's the same assy inside, just not accessible for replacement.