MY 2011 PRIUS SHAKES WHEN APPLYING LOW GAS

For a car that age with that many miles you will likely have a few more issues down the line. If you're intent on keeping it, the first order of business would be to get your hands on a copy of Techstream and a suitable cable.

Even if you don't perform your own repairs, Techstream lets you perform active tests that can help you diagnose issues. That way you're not relying on the dealer or mechanic every time you need a diagnosis, and you can give forum members specific information pulled from the software so they can point you in the direction of a fix.

 

Likely head gasket failure. Very common with those miles. Unscrupulous owners add stop-leak to mask symptoms. Assuming the EGR system (Exhaust Gas Recirculation) and intake manifold have not been cleaned, they will be choked with carbon, contributing to the head gasket failure. Toyota is dodging the issue.

 

The symptoms described in post #1 are rough engine running that does not happen at idle, does not happen at high load, but does happen at moderate load.

The car's Exhaust Gas Recirculation system is not used at idle, and not used at high load, but is used at moderate load. Therefore, the symptoms being described correspond to when EGR is being used.

The intake manifold contains small passages for the EGR to pass through, ending in small openings within each of the four cylinder ports. Those passages can become slightly clogged so that different amounts of EGR flow to the different cylinders. This has, of course, no effect at idle or at high load, when no EGR is used, but will make the engine run roughly at moderate load where EGR is used. The symptoms described match this pattern closely.

It is not a long or difficult job to remove the intake manifold and clean its EGR passages.

A person doing that job might also choose to clean the rest of the EGR system at that time, though the job gets considerably longer if that is done. The upstream portions of the EGR system are common to all four cylinders; they can be clogged to some degree or other, but that doesn't cause imbalanced flow to the four cylinders, the same way clogging of the manifold passages does.

Mendel's suggested diagnosis of head gasket damage usually presents with different symptoms, such as rough running only when the engine is started, after it has sat for a while. It is not commonly associated with the pattern described here.

Mendel is invested in a theory that head gasket damage is caused by restricted EGR flow, and so (a) he is likely to give a strong recommendation that the whole EGR system be cleaned, and also (b) he is wont to say it's too late and cleaning the EGR won't fix a head gasket that is already damaged.

(b) is true, of course, when the symptoms really are because of a damaged head gasket. On the other hand, symptoms like the ones described here usually aren't caused by a head gasket problem; they are simply caused directly by an imbalance in EGR flow because of clogged manifold passages, and there's no reason for thinking it's too late for those to be cleaned. The mid-load rough running will probably stop when they are.

 

For head gasket failure, a boroscope inspection of the combustion chambers, preferably with the engine coolant system pressurized, might help with the diagnosis. You're looking for "tears" of coolant. Tends to start with cylinder one. A leak-down test would also be good.

Perhaps I tend to jump to conclusions, as explained by the professor above, so take me with a grain of salt. Consider though, the car has 242K kms (159K miles): this is more or less the appointed time for head gaskets to let go on third gen, in particular with neglected EGR cleaning.

Consider also: the car was for sale, with those miles. I wouldn't touch a third gen Prius with those miles; there's one tediously regular reason they're for sale. And part of the "sprucing up" tends to be a bottle of stop-leak, which just compounds your problems: everything in the coolant circuit is gummed up with that junk.

 

Yes look at your EGR all of that business It's probably plugged up your intake manifold those little passages chap is talking about are probably 60% closed or something You look and tell me and then on top of that it is very probable that water is quenching the fire in one of your cylinders or adding to not full combustion causing a miss which causes a stumble and a rattle this is an open deck engine design and you want to be very careful about how much money you throw at this engine with this problem It will get away from you quickly so just be aware of these situations as people are telling you you need to spend $5,000 etc this will be the next series of conversations oh and good luck.

 

welcome!
i had those exact same symptoms on my 2012. cleaning the egr circuit was too much for me, and i couldn't find anyone willing to do it, so i traded it in.
all the best!