Hi guys. I own a 2007 Toyota Tacoma SR5 PreRunner 2WD 4.0 L. I looked for this topic because this is

Hi guys. I own a 2007 Toyota Tacoma SR5 PreRunner 2WD 4.0 L. I looked for this topic because this issue of chronic, alternating check engine light and blinking engine light had been a regular occurence for me since summer of 2019, plus the infamous DTC P0306 which is now a familiar fixture for me. Don't get me wrong it is still a bad ass on the road. But, coming out of nowhere, something triggers it, then these pestering DTC P0306 pop up, and if you are not used to it, could stall you, like it did me once, in from of my son's school 4 way stop sign.

Background of the problem: we were driving it in August last year here in Southern CA, as we were shopping for an apartment; we were apartment hopping practically everywhere looking for that ideal place. As we stopped in one of the guest parking spots, I ran the engine idle for about 5-8 minutes. That was when I saw the A/C button started to blink as we steadily lost cool air. Turned it off. Then back on. Never went away. When we took a break in our search to pick up our youngest in his school, the A/C system went back to normalcy.

However, as I approached the schools 4-way stop sign, the engine choked and stalled. Took me 10 seconds to fire it back. As we sped to our old house, I noticed that the thermostat started to rise to near overheat levels. Since we were only about a quarter of a mile from our house, I went on. That's what when I saw white smoke in front of the engine bay. I lifted the hood. and discovered that the large hose connector hooking it to the thermostat housing was disconnected, basically spilling coolant on the road.

Here was what I did: 1. Did a radiator flush, the small radiator under the dashboard included. The radiator flush would have been it, but I had lingering doubts: did I blow my gasket? 2. I removed the thermostat from the housing and had the truck ran on distilled water. Did a test run without coolant and it was ok, no overheat. 3. I put blue devil thinking still of my gasket. That was when the dreaded DTC P0306 started popping up. I have an OBD scanner, ignored it by clearing but it was a nightmare of alternating check engine and blinking check engine light. 4. Compression test was negative. I did remove the intake manifold and replaced the valve cover gasket. No good as the code persisted. I checked all the vacuum hoses and replaced the PCV valve and its hose connector. The problem persisted. 5. I replaced the spark plugs, checked the wires, switched the coils but it still persisted. I checked the cylinder for presence of oil or coolant but found nothing. 6. Finally, before the move to our new place, I replaced the belt and realigned the marks to TDC and checked the valve clearance which was still within specks since it was already opened.

The issue was never resolved. Today, the dreaded choking came back and kept popping up even though I cleared with it my OBD scanner but I am suspecting that the vacuum hoses are the suspects for the code this time. I have a hard time accelerating and I could feel the lack of pressure, and intake of air is wanting.

Please help. What did I miss? I maintain our 3 Toyotas but so far this was the most challenging. Thanks.

Last edited: Yesterday at 4:21 PM

 

Any expert insights, folks? I will wait, hopefully I generated enough hits for members to react, including the mechanics, DIYers like me, so I can eventually solve this issue. Funny, even with check engine lights blinking, last Monday night, I and my wife drove to San Diego. The truck did not act up for some reason, no check engine lights, so I thought the problem went away. However, the following morning, as I drop by my bank, the check engine came back, no choking or hard start though. What is my truck telling me? No CEL on the 5 FWY but on city streets it blinks light crazy. I need your input.

 

So you're saying that you switched the coil pack and the problem stayed with your #6 cylinder and didn't follow the coil pack? This one's new to me. How does your timing chain look? Any teeth worn or stretched links? Maybe the tensioner is starting to wear out on that side.

-J

 

Thanks for the question. Actually I switched the ignition coil#6 with #4 and #5. Looking back, when I had a driveway and tinkering with cars were never an issue in the former place, I should have switched it with #3, and I did not. And believe it or not, the misfire stayed on #6. It was not the coil, or sparks, as they were all replaced.

 

And oh by the way, as for the timing chain when I replaced the valve cover gaskets, checked the valve clearance and aligned the timing marks, it looked pristine, like new. Did not see any worn teeth or stretched links. I replaced the tensioner in 2018 when I replaced the water pump and the corresponding parts.

 

Is it possible that the valve cover gaskets had to do with this? If oil was leaking on the gaskets, could it cause a misfire and a blinking check engine light that ends up stalling the truck and loss of pressure or speed?

 

I'm not 100% certain that a faulty valve cover gasket would cause a misfire but just because I haven't seen it happen in the past doesn't mean it cant happen. You said piston was holding pressure so that weeds out your piston rings/seals. When you did your valve cover, did you torque down all the head bolts correctly? Star pattern (crisscross)? Are you suspecting a head gasket leak? Pull your radiator cap when the engine is cold and run your vehicle, check for bubbles rising in the coolant. With that said, I don't think that would cause your intermittent code. Do you by chance have a rodent issue where you live? Rats/mice like to get in the channel between the heads to keep warm. They may have chewed on your ignition cables or the wiring that's between your banks. You'll have to pull a lot of stuff off again to check or you could rent a bore-scope from an auto shop and look. If there's a lot of nesting debris in that channel, I would suspect that is your problem or at least one of them. I've also read that it may be your fuel injectors. Could you try swapping the fuel injector from #6 to #3 and see if it follows that? If that's the case, then I suspect you may need to clean your injectors and change your fuel filter. It'll be in the tank so you'll have to drop the tank or pull the bed (read: slide it back), which ever's easier for you to do. There's those STP fuel injector cleaner bottles you can buy and run through a tank but I don't really trust them. It's akin to running Draino through your pipes vrs using a plunger.

-J