Idles roughly until accelerator pressed

07 Prius with about 180,000 miles. The engine shakes badly and has a knocking sound on startup and while idling. If the accelerator is pressed slightly the engine smooths out.

I have replaced coils and plugs, cleaned the MAF sensor with proper cleaner, but the engine still runs rough.

The fuel injectors were replaced with new ones a few years ago.

All the old plugs had oil on them and a couple were badly burnt.

Any thoughts on what I should check next?

 

I’ve cleaned the throttle body in the past and checked it recently. No visible build up although I do see oil pooled at the bottom.

The engine knocking sounds are violent. But it does cease when giving a bit of fuel.

Unfortunately I could not read the engine codes to see if the misfires are no longer present.

Would dirty fuel injectors be a potential cause? I put new injectors in about 3 years ago.

 

NAPA Echlin Part #: CRB 238724

 

Sorry for the slow reply, thanks for responding. This is my dads car so it took a while to get the answers. And I was just able to check the engine codes today.

Oil burn rate?: approx. 1 quart every 5,000 miles
Did the knocking/shaking change?: less knocking after and it smooths out when pressing the accelerator slightly, but still misfiring
Have plugs been changed before?: Yes, 3 years ago. When changed this time they were covered with oil and burnt.
PCV valve checked?: that’s next. I bought a new one from Toyota and planned to replace it.

The fuel injector replacement I did 3 years ago originally solved the problem. I also sprayed the MAF sensor with proper cleaner and cleaned the throttle body at that time.

I cleaned the MAFS again this time and checked the throttle body which didn’t look too bad.

Just checked the codes again. Random misfires on cylinders 1, 2 and 4. P0301, 302 and 304. That’s with new plugs and coils. What are the odds that those injectors have problems? Would the pcv valve make that much difference? Is ECM a potential problem?

Obviously a trip to a decent mechanic for full diagnostics is probably necessary but the collective knowledge here is usually very helpful.

 

Any more thoughts on the symptoms as described? Thanks

 

Still looking to do the engine check.

Coil packs were Toyota parts, 90919-02240. I checked and that was an exact match with original part. Plugs were either Bosch or NGK iridium plugs from the local parts store.

My dad has always changed the oil religiously every 3000 miles. The car only began losing oil after a dealership pulled the injectors out years ago without permission. They were instructed to put them back rather than my dad paying them $1200+.

Wondering if the replacement injectors could be a problem again. The car ran great for a few years after changing them.

 

Thanks for the reply. Not yet but hopefully soon. Planning on ordering a new set of injectors and plugs from Toyota again to replace the existing parts that I replaced earlier. Also a new PCV valve. New Toyota coil packs are already in along with some other recommend parts.

This is strange because the car ran great for a couple years after putting in the plugs and injectors. Maybe something is causing issues with the injectors.

 

Great advice. Root cause may be something else since the first replacement set was NGK purchased from a local auto parts store. And those plugs went bad prematurely. But maybe they weren't as good as Toyota source parts. I'm ordering plugs from Toyota and will also check the injectors and probably order those again new from Toyota. The fact that gently pressing the accelerator smooths out the idle seems to be a clue pointing to fuel issue.

I don't know, the first change of plugs and injectors worked wonders. This should not be so difficult to troubleshoot. Will just have to divide and conquer per the good advice given here until it's working. Most difficult step will be checking compression.