Rough Start

The plug wires are arranged so that water can collect and seep into the spark units (whatever the coil replacements are called). There is a sealing compound that is supposed to prevent this, but it can leak over time.

Tom

 

The Prius (and most newer cars) has Coil on Plug technology. Instead of high voltage plug wires that lead from a coil (or igniter) it has a separate coil mounted directly on each spark plug. There is a low voltage signal sent by the Engine ECU to fire each coil at the appropriate time.

The water issue that Tom mentions is a possibility, or maybe just worn spark plugs. The plugs are supposed to be good for over 100k, but they degrade over time, so a change of plugs may help.

 

I belive they're called "ignitors" now, all self-contained. Power,
ground, trigger input, and the IGF "I went zap" feedback lead.
.
There's no sealant around where they insert into the head, just
rubber gaskets. If enough water piles up on the valve cover it
has no place to go and would eventually leak down into the ignitor
wells. Some Priuses have had trouble with this if the rain-gutter
cowling or the hood gaskets failed to keep water off the engine;
corrosion could start down around the plug electrode and make
a shorting path to the block.
.
There's a tiny weep hole at one place around the circumference of
the ignitor gaskets; I assume these should be at the back as it's
the downhill side, but it goes into sort of an air-channel maze so
it may not matter as it's probably more for pressure equalization
rather than actually helping drain water.
.
Might be prudent to pull the cowl off and remove the ignitors
and have a look down in there, clean things out, and if you've
never had the plugs out also crack 'em loose carefully and get
some anti-seize onto the threads.
.
_H*

 

No, he has a 2008 so it's not likely to be worn plugs. It's possible there was a poor connection in the wiring. Some new cars experience this. It usually corrects itself.

If the oil is thicker than recommended the Prius engine will run rough when cold. Have you changed the oil yet? Did you/they use 5W30? 10W30 can cause rough starts/rough shutdowns.

Dew doesn't usually get under the hood. As stated above, the Prius has "coil on plug" technology. The high voltage is deep inside the valve cover sparkplug tube. What you see on the top of the engine is the coils.

I wouldn't worry unless it becomes repeatable.

 

Injector cleaner you add to the tank is at best a placebo. You wouldn't need it even if it worked until you got way more than 60,000 mi on the car.

The way they "clean" the fuel system and intake tract is they disconnect the fuel line and run straight cleaner into the engine.

If you have old injectors which really need cleaning, they remove them and send them out to a professional cleaning service. They run them with very strong cleaner in a special box, measuring the flow before and after cleaning and giving you a printout. Usually this isn't needed until -well- after 100,000 mi is on the engine.

Because the Prius engine isn't heavily loaded it is unlikely you would -ever- max out the injectors. The ECU automatically adjusts the injector pulse width/rep rate to compensate for poor fuel or clogged passages in the injector.

 

Just for fun, check your throttle plate for smooth rotation. It isn't very likely but the humid morning is consistent with the problem I'd had.

Bob Wilson

 

fyi--I also have a 2008 and had this happen to me as well. Only once, about 3 weeks ago.

Car shook for about 5 seconds, no problem since.

 

The ECU learns over time. If you usually garage it, but left it out this time, it may need to learn a new startup profile. Until the cat and O2 sensor warms up it is in a programmed (open-loop) mode, not closed-loop, and the "old" program that worked before may not be right for the new conditions.

 

.

 

This is graet info my 2002 has a rough start sometimes. I still use an injector cleaner every 3 months hoping to keep it clean for $2-3 I can't complain. I assume is works.

 

Any chance it could be some condensation[water]in the gas or crude. H

 

You got to be careful with fuel additives as they can harm Cats and other pollution devices? Just buy good quality fuel. H

 

I have a 2005 Prius 170,000 miles (273.5 km) driven so far.

Experienced rough cold start up for the first time a couple of weeks ago. It only happened at first start up and only for a few minutes. Felt like a cylinder was not firing. Couple of days of this and the check engine light went on.

Took it to the dealer (Manhattan Beach Toyota, California). They had to keep the car for a couple of days because the symptoms were so short and only when the car was cool. They needed to make some measurements to be able to get some idea of the problem. Ended up replacing all 4 coils and spark plugs. Two coils were measuring out of spec and a third one was boarder line.

A week went by and car started up fine. Then the rough start started up again. No engine light warning this time. I took it to the dealer again. They kept it for another couple of days to run some tests. They even requested the Toyota Corporate Engineers to come over and take a look at the car. They determined that the Mass Air Flow Sensor was dirty. So they cleaned the sensor and area around it and did some calibration adjustments. It has been a week and the car is starting up fine.