Junior Member
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Join Date: Apr 2014
Location: Wisconsin
Posts: 7
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Junior Member
Join Date: Apr 2014
Location: Wisconsin
Posts: 7
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Solved rough idle, multiple P0300 errors after valve cover replacement
Greetings, I thought I would relate my experience after doing what I thought would be a not too difficult valve cover replacement.
Spoiler: The problem was that I had a air leak in the lower intake gasket.
Now for the Tale and the Troubleshooting:
Vehicle:
1997 4Runner Limited, Automatic with the 3.4 L V6 engine, 235K miles.
Issue:
I was getting tired of smelling burnt oil, that seemed to be leaking from the valve cover gaskets. After researching a bunch of articles and videos from this forum I decided to order new valve cover gaskets, Cam Plugs, Spark Plugs and intake manifold gaskets and do the job.
It took me about 8 hours, with a good 4 hours cleaning the valve covers, removing crud, cleaning the 4 1/2 moon cam plugs, installing the new spark plug grommets.
When it was all finished, everything connected, I went to start the car and it idled terribly. At 750 RPM it would die. Above 1500 was OK. I was bummed!
I spent the night looking over this forum trying to think what it could be the problem. I'm a big believer in cause and effect, so what did I change that would cause this problem?
The next morning the first thing I tried was to clean the very dirty engine ground on the driver side of the intake manifold..... No change.
I then tore everything apart with the exception of removing the valve covers, double checked, put it back together... The idle was a little better, but still rough. I went for a 7 mile test ride and then check the engine codes and saw:
P0116 Engine coolant temperature sensor Rage
P0171 system too lean Bank 1
P0306, 0305, 0303, 0302, 0301 (misfires on 6,5,3,2,1)
Cleared codes, ran again, sprayed carb cleaner near center of intake manifold near fuel rails.
RPM increased (maybe leak in the gasket, it is a hard metal gasket)?
Got: P0130 02 Sensor Circuit (Bank 1 Sensor 1)
P0133 02 Sensor Circuit Slow Response (Bank 1 Sensor 1)
Pulled ELM fuse, reset it, no difference.
As the engine is running I started spraying carb cleaner around the vacuum hoses and intake, and near the front of the intake on the bottom, I could hear a RPM increase.
This morning I pulled of the intake, and noticed on the bottom of the lower gasket there was a small 1/4" roundish buildup of smudge, that almost looked like compressed graphite. I cleaned up (again) all 4 mating surfaces of the intake system, put in new gaskets (again, but this time I tried the fel-pro brand), the previous new gasket was LIMICAR brand.
I put everything back together, hit the key and it started right up and idles like it should. Went out for a 10 mile test ride, and it runs great! No idle issue, no engine codes, will idle at 750 RPM just fine.
Thinking about the issue with the air leak in the lower part of the intake it all makes sense.
When at a low RPM, below 1500, Too much air was getting into the engine causing random misfires on each cylinder and also other engine codes including the P0171 system too lean Bank 1. At a higher RPM the small amount of air sneaking in was not enough to affect the larger volume air entering the engine.
Well I spent about an additional 10 hours trying to understand/fix this issue, but I learned a few good lessons.
1: If something is not working, what is the last thing you changed.
2: Engine Idle/Misfire issues will be related to fuel, air, spark. First check what you worked on. I was pretty sure spark was good (new plugs), fuel should be good, I did not touch the fuel system, that leaves air.
3: A small leak on the intake manifold can disguise itself as different issues.
I had all these codes all because of the intake leak:
P0116 Engine coolant temperature sensor Rage
P0171 system too lean Bank 1
P0300 Misfire detected
P0306, 0305, 0303, 0302, 0301 (Misfire on specific cylinder)
P0130 02 Sensor Circuit (Bank 1 Sensor 1)
P0133 02 Sensor Circuit Slow Response (Bank 1 Sensor 1)
Attached are pictures of the offending issue:
-andy
Last edited by AndyFromWI; 01-19-2020 at 11:16 AM.
Reason: Added Image
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