Stumped by P0301 and P0302

This has been an ongoing issue with our 2006. We purchased the car about a year ago and have put on just over 8,000 miles. Rebuilt the battery pack and replaced the 12v battery. This is my wife's car and I have a 2005, so I have done some diagnostics, tuneup, and even swapped some parts between the two cars trying to narrow down the issues.

Only recently have codes been recorded. The car is has a noticeable misfire at low RPM. Here is what has happened up until now:

11/29/15 - replaced spark plugs - #1 was fouled so I swapped coils between cylinders 1 and 4

2/25/16 - replaced 12v battery with new battery

4/1/16 - P0300, P0301 codes were first recorded and reset to see if they came back

4/10/16 - swapped Integration Relay with my 2005 (part # 82641-47010). My 2005 ran poorly after the swap, so I put a used one in my 2005.

5/29/16 - P0300, P0301 were back. Replaced plug again on cylinders 1.

6/23/16 - Codes P0300, P0301 were back. Swapped 12V batteries with the 2005 - no change. Put new seals on all 4 injectors.

7/9/16 - After a test drive, code P0301. Codes cleared.

7/10/16 - MAF sensor cleaned and swapped with 2005. A bottle of HEET added to tank and tank was topped off. Codes cleared.

7/16/16 - Codes P0300, P0301. Codes cleared.

7/17/16 - Throttle body swapped with 2005 and cleaned thoroughly. I verified with my Mini VCI that both O2 sensors passed their checks. The only issue it seemed to record was misfires on #1.

7/24/16 - Downstream O2 sensor swapped with 2005. Cleared codes. P0301 code came back after a short test drive.


A few notes - My wife has been driving my 2005 since the 2006 started having so many issues. I have been driving my old truck. The 2006 is misfiring so badly that it isn't practical to drive and hasn't been driven except for test drives since 6/23/16. As I have been able to do some test drives with my Mini VCI, I have noted a few things. The car stumbles like crazy when it is below 1,200 RPM, records lots of misfires on #1. Once the engine gets above 1,300 RPM it does not seem to record any additional misfires.

Any thoughts?

 

It is at 207,000 miles. We bought it at 199k. It uses some oil, but not anything more than I would expect for a car of this age/miles. This doesn't use any more oil than the other Prius.

 

Thanks guys. That gives me some things to think about. I figure it is something that I am just overlooking. Easy to miss something to check off the list. I was going by the factory manual (PDF version online). The P0301 misfire on #1 is keeping the car from being driven.

The MAF and throttle body were both swapped with the 2005 and cleaned. Neither one made a difference in either car (would have expected the 2005 to crap out). The plugs are NGK, just as factory. I hadn't given much thought to the EGR, so I will likely try to tackle that as time permits.

Regarding the fuel PSI, I wanted to test it just to rule it out. I don't suspect it as the problem, but better to make sure. If it were the problem, I would likely see random misfires across all cylinders, right?

 

When I replaced the plugs in November it was because the car was running poorly. The car hadn't given any sort of codes at that time. I didn't know when the plugs had been replaced, or what type of plugs were in it, so I decided it was cheap maintenance. Turns out they were not terribly old and were NGK. #1 had fuel on it so I deduced there was a misfire occurring. Decided to swap the coil packs between 1 and 4 to see if it made a difference. No such luck.

 

I have given it some thought. Trying to avoid that as it could be a fair amount of work. I have been trying to tackle the simple stuff first. It is still on my radar as a possibility.

 

So I have some "updates". Unfortunately so.

I haven't done squat really on my wife's 2006. Shortly after the last update, we found her a 2004 Subaru Forester XT (250hp and AWD) for $1,500. She wanted a Subaru again for winter driving since we live just outside Denver and can get considerable snow. The 2006 has just sat with the #1 misfire. I start it from time to time for a minute or two just to keep the engine moving and the battery charged up a bit.

The worst news is that my 2005 now has the EXACT same problem as the 2006. Misfire on 1&2. Just started this morning (the wife tried to drive it after blowing out a Forester tire on debris in the road). The worst part is that it is a BAD misfire. The engine logged around 1,000 misfires within a minute or so. It sounds like it too. Planning to swap coils and plugs with 3&4 to see if anything changes. May also try a full set of new or rebuilt injectors.

 

Good news is that I fixed the 2005 this evening. 4 new plugs, plenty of dielectric grease, and replacing 2 coil packs solved everything. It went from about 1,000 misfires on 2 cylinders every minute down to just 2 recorded misfires on a single cylinder over a 30 minute drive.

Now it is time to tackle the 2006 again. Since it had the same symptoms and codes, maybe I missed something the first time around. As time permits, I will go through the ignition parts and report back. Fingers crossed!

 

The 2005 has been running like a top again since replacing the bad coil pack.

So today I did some more work on the 2006. I put in 4 new plugs with dielectric grease, 4 new coil packs. No change. Then I swapped injector 1 for 3 and 2 for 4. Still no change. So I am still dealing with P0301. This seemed to resolve the P0302 that I had intermittently seen. Nothing seemed to make a difference for the P0301 though. Still plugging away at it.

When I took it out for a test drive, the misfires still all occur at low RPM. When I am on the highway cruising, it doesn't log any. It only really seems to log any when the ICE kicks on, so basically city driving.

For anyone interested, this is exactly how it sounds at lower RPMs:

 

Yeah, I need to see if I can figure out how to do a proper compression test. Will post results if I do anything.