Helpful insight for code P0303 coupled with a bunch of other codes (long story... experience)

Helpful insight for code P0303 coupled with a bunch of other codes (long story... experience)

Codes experienced:

P0303 - Cylinder 3 misfire

P0120 - Throttle pedal position

P0441 - Incorrect purge flow

P0450 - Evap emission system pressure malfunction

Scope of problems:

First off, I’m not an auto mechanic. This entire log has been a journey for me and I gained a lot of experience that I’m thankful for. I hope my experience will help others in similar situations in the future. Sharing this log so you don’t have go through the same headaches.

Within the past year or so, my truck has put me through hell. At first I had no check engine light, no codes... zero problems. I opened the can of worms on myself when I decided to clean my throttle body, the IAC and MAF sensor, new air filter. Thank you YouTube...

Then the problems came... and they came!

Immediately after doing these maintenance procedures I was experiencing a rough idle. So I repeated the cleanings of all these components with no improvement.

Then I replaced the IAC with a new looking OEM one I pulled from a Tacoma at the junkyard, with a new gasket from the local parts store. I also replaced my TPS pulled from the same truck. Still rough idle... no check engine light this entire time, up to this point.

Then the check engine light turns on with code P0303. So I changed the spark plugs and it went away for a good period of time before it came back.

Code P0303 comes back coupled with P0450 and P0441 this time. I replaced the spark wires and the evaporator pressure sensor. Thankfully my friend had the sensor laying around, this sensor is expensive and hard to find OEM.

Code P0450 and P0441 went away permanently, thank the Lord. Code P0303 also went away for a good period of time...

Code P0303 comes back! This time I swapped coil packs with cylinder 5 to see if the coil pack was malfunctioning. Then I got codes P0303 and P0305(cylinder 5 misfire) this time. So I know for sure cylinder 3’s coil pack was damaged! I replaced all of my coil packs for the sake of good measure.

Now all codes are clear for long time, but now there’s still an intermittent rough idle here and there. Even though rough idle decreased dramatically after replacing coil packs. Only once in a while now, I knew I was making some progress.

At this point, I started looking into possible vacuum leaks. I’m thinking maybe my intake tube, resonator or vacuum tubes are leaking. There were cracks on the ends of the rubber intake pipe. I replaced the intake pipe, waste of time.

So then I’m like F... it, I decided to install a K&N cold air intake out of boredom. The once in a while intermittent rough idling continues, still no codes for a long time.

After another long period of time, guess what happened? Yes... code P0303 comes back. This time it’s coupled with code P0120. I immediately changed the TPS again, this time with a brand new one I had sitting around just incase, WVE brand. The check engine light and codes went away again, but the intermittent rough idle is still there.

I began to trace vacuum lines to see where they go. Surfing the internet for any and everything I could find that can cause a rough idle. I was deep in the rabbit hole reading and I came across the PCV valve. I bought one right away, got the OEM PCV with a new grommet off eBay.

Replaced the PCV and the the rough idle went away. I could have cleaned it, but I didn’t want to go through any hassle anymore.

The PCV valve guys... My advice is to replace the PCV before throwing money at anything else when this happens. Can you believe it? All of these problems were triggered by a throttle body cleaning, unbelievable.

My guess is something was thrown off balance after removing all of that nasty buildup in the throttle body and IAC. The system was no longer cohesive.

I’m happy to have shared my experience with you guys. For all the noobs like myself, this thread is GOLD.

 

PC valves are easy to replace as long as you don't jam the grommet into the valve area.

Like I did.


It took some very careful fishing but I managed to pull it after 15 minutes of futzing around. One of those cheap hook and needle kits from Harbor Freight helped me quite a bit.