Car misses horrible at times at idle and lower RPM's, shakes the whole car. MPG around 32. Runs better when car is fully warmed up. P0171 and PO 300, 301 and 304 codes come up. Here's what I've done so far to try to correct the problem: Cleaned mass air flow sensor. No change. Replaced mass air flow sensor. No change. Replaced plugs and ignitors (coils). No change. Replaced PCV valve. No change. Replaced upstream O2 sensor. Same codes come up but MPG increased to 37. Replaced throttle body. No change. Car does not miss when accelerating hard. Sometimes runs perfect at idle and lower rpm's, but mpg is way low as it used to be in the 50's or higher. Car idles perfect in neutral. Always runs perfect the first 3-4 seconds when you first start it, then starts shaking. If I put my finger in the throttle body when it's running poorly, apparently disrupting the air flow a bit, the idle smooths to perfect. It's some kind of fuel-air problem, but I can't seem to figure it from here. I have an extra computer, although I don't know if you have to program the key for it to work. I don't suspect this is the problem anyway. I haven't changed the fuel injectors. I can't hear a vacuum leak. I've read a few stories online with folks that have the exact same problem....but none of them ever posted a solution that worked. The only things I'm looking at trying at the moment is the intake gasket and injector seals, although I could probably test those for a vacuum leak with a spray bottle .
This is a good idea. In addition I suggest that for fun, you disconnect the negative 12V battery cable for a few minutes, then reconnect. See if that makes any difference. The idea is to give the engine and hybrid vehicle ECUs a chance to reset. The hybrid vehicle ECU has to cooperate closely with the engine ECU to get the engine to idle, since MG1 has to counter-rotate to allow the engine to operate at idle speed. When I owned my 2001 I noticed that from time to time the engine would act like you were driving a manual transmission-equipped car, were coming to a stop, and failed to depress the clutch pedal as you were slowing down. This was because the hybrid vehicle ECU was not spinning up MG1 appropriately.
I checked the injectors. The gaskets are in poor condition, but aren't leaking. The intake isn't leaking. I disconnected the 12v battery, but the same codes come back. I took it for a 60 mile drive. The engine was running perfectly. 53mpg in town at mostly 45 and 30, with the hybrid battery doing much of the work. At 55, the mpg was 38. At 72, it was 28. Got home, car running perfectly, shut it off, start it again and it almost shakes you out of the car....and the process starts over of driving for a bit, the engine smooths out after a short while, then runs fine but with low mpg. It should get around 50 at 55mph and 45 at 72mph from past experience. Also, when the engine is shaking all over the place and running poorly, disconnecting the mass air flow sensor makes the idle perfect for about 3 seconds....then back to the shaking.
The first few seconds it's not running, it's going through a start up procedure. I've seen similar symptoms on a very high mileage engine (260k) How many miles on the car (and where is the car located?) What is the history of the car? Have you owned it for a long time and it recently start doing this stuff or did you recently buy it at an auction or similar?
It has 165K. I bought it locally cheap. I'm in MN. The previous owner had the car for 5 years and said it had been running like this for some time, but didn't have the funds to have anyone look at it. The car always starts and drives and the hybrid battery and system seem to be rock solid. No smoke and clean oil...the motor seems to be in good shape and the the CVT works fine. I figure it's worth fixing. I know approximately what the mpg should be from owning a 2001 prius in the past.
If you have a donor car for parts, try swapping the crank sensor at the bottom of the drive belt crank pully, especially if the electrical connectors is damaged and water/oil/dirt have gotten into the wiring.
I'm going to try a few inexpensive things.....change the injector seals and intake gasket. I don't think they are leaking but they are cheap and easy to change. The new mass air flow sensor I bought was only $20 and the car barely ran I tried it. A new exact Denso is $75. I tempted to try that also.
It sounds like there may be a mixture control problem. I would probably start with: fuel trim values, O{2} voltage swings - looking for evidence the car may be trying to adjust but running out of 'headroom' fuel pressure? - a weak or failing fuel pump with engine air filter removed - does "finger" blocking or a spray fuel (aka., cold-start can) have an observable effect on roughness? - indicating too lean, not enough fuel flow, or too rich, stalls it out taking extreme safety precautions - a 'rag soaked with gasoline' on a coat hanger . . . a primitive, 'hillbilly' carb, DANGEROUS . . . can of cold-starter is much safer . . . this is a farm tractor or a lawn mower, right? I'm grasping at straws here. Bob Wilson
P0171 indicates mixture too lean, which is completely consistent with the idle improving when you restrict air intake. The other codes just tell you it's misfiring, which is just the result of the problem. Either too much air is entering the engine at idle, or not enough fuel. From your later posts it sounds as if you've ruled out vacuum leaks in obvious places. Have you ruled them out in all possible places? If too much air is ruled out, attention turns to fuel delivery - fuel pump pressure and capacity, or injector condition. Fuel pump pressure test shouldn't cost too much at a shop ... I haven't tried to DIY that because the set of tools and fittings I'd need to do it would end up getting used probably once and then taking up toolbox space. There are services that will test injectors and give a written condition report for about $8 each if you have time to mail them away, and if their condition warrants you can have them returned to you reconditioned, which adds another $12 each or so. You might find local shops with the same equipment offering the same service. My own experience with an injector service (I didn't have any P0171 code, I was just curious about their condition at 205k) was that they tested in very good condition and I probably had no need to service them. But in your case there is a P0171 and if you completely rule out air leaks, fuel supply is next. -Chap
