3.4L, Rough run after Hot Restart

Over the last month, my 3.4L V6, 4x4, SR5 has run into a complicated-to-diagnose rough running engine.

When a cold engine (first start of day or shut down more than 2hrs) is started and driven, I have zero problems. If I shut the engine down right away and restart it, no problems. However, if the engine is left shut down for 15-20 minutes (like if you go inside a grocery store), and then attempt a restart, it runs incredibly rough. At first, I would start to drive despite the roughness and it would clear up 100% after the first mile of driving. Now, it continues non-stop.

I was only able to generate a code once- P0303. Once I cleared the code, it never returned over several weeks. Today, I ohm checked the coil pack and fuel injector for the #3 cyl. All were within spec. I swapped the spark plug for #3 cyl with #1 cyl for giggles but no change.

1999 Toyota Tacoma. 3.4L V6, Manual. No mods. The engine has 228,000+ miles on it. All spark plugs, leads, and wires were replaced about a year ago. I cannot understand why the engine runs so well except after a hot start after it's been sitting for 15-20 min.

Thoughts or suggestions?

 

Engine coolant temp sensor or sticking EGR valve.

 

X2 on ECT sensor. When it goes out the sensor tells the ECU that the engine is cold (although it isn't) and dumps in more fuel for a cold start thus making it run rough.

 

Fuel pump.

You can find the Denso pump on rockauto.com for $100 and it takes 2 hrs to replace it.

 

Will look into ECT sensor or EGR on my next set of days off.

Meanwhile, new symptom is it randomly died at an engine idle value when it was running smooth.

Still no codes being thrown.

 

I was going to say fuel injector. My runner did this at 165k. I let it go then the check engine light came on and it would flash. Took it to a buddy who is a Toyota mechanic said that's the only time the check engine light will flash.

 

Decided to drive it around a little more just for grins. It's now throwing a code more or less continually, a P0303. I'll clear the code and it's the only one that keep reoccurring. I am going to guess that it's a fuel injector. The multi-meter may have been throwing me off since it was reading "in spec" but was done with a cold engine. The heat may be causing it to fail which explains why it runs rough when it's hot.

 

Your welcome. Hope you get it fixed. I did not have to diagnose like you I took it to my buddy who is a Toyota mechanic and he figured it out and fixed it. Good news I fixes the one bad one and its been running like a champ ever since my gas mileage has improved since the fix as well.

 

If you are consistently getting a P0303 then it is misfiring on Cylinder #3. The causes could be:

-Bad spark plug
-Bad spark plug wire
-Bad coil
-Bad Cam Sensor
-Bad Crankshaft Sensor
-No compression.

I just went through this on Cylinder #6 on my truck. I had 100,000 miles on my plugs and wires. I checked the plugs and wires and everything was in spec. I decided to put new plugs and wires on anyway. It fixed the problem.

I bet the order of likelihood is in descending order as I listed it. Have you tried plugs and wires? Have you switched the coil pack positions to see if it stays with Cylinder #3 or jumps to another cylinder?

I would try that next.

 

I did too same code and same things he is going through I changed most of the list you said and then I took it in. It was an injector.

 

Gave up troubleshooting and took it into a shop that only works on Toyota/Lexus vehicles.

The P0303 code only comes on every once and a while. I was shocked when they called me and said they also weren't sure what was going on but wanted to start with the plugs and wires. Well shoot, I can do that myself and save the labor.

I replaced the plugs and wires with genuine Toyota parts...problem remains, unchanged. Taking it back next business week for them to continue troubleshooting.

I figured shops that had high levels of experience working on these engines could have a higher tech way of diagnosing the problem. Sounds like they are just doing what I was doing...throwing parts at it till the problem is fixed.

I'll keep y'all posted..

 

Resolution: New fuel injector for #3 Cylinder. Old fuel injector was only acting up with heat after a sit. Have driven it for half a day post repair and all seems to be well so far.

Lessons learned: Multi-meter mislead me by providing a correct resistance per the Haynes manual. Since the injector was intermittently failing, I must have used the multi-meter when it was intermittently working correctly.

Thanks to all who posted solution advice.

 

Bad temperature sensor. It controls fuel like a choke

 

Run some Lucas fuel injector cleaner through it. Will not hurt anything. But - most likely just a band-aid

 

First post to bump a 5 year old thread? I like your style.

 

Post #12: bad fuel injector