Slight miss, a real head-scratcher!!

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Ggradtech

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So I recently developed a slight miss. Seems to be an issue once the vehicle is warmed up, and doesn't happen when its cold.
As a needed "preventative measure" due to the fact that it has 210k on the clock, I had the original injectors professionally serviced/overhauled/bench tested, new coils, plugs and wires. After this, the 4runner ran much better. I did this work yesterday. Today it ran great when I first drove it for about 30 minutes. I then parked it for about 30 minutes and then when I started it and drove again, the miss came back. It stayed like this with the miss/shuddering for about 30 minutes of driving. Idle seemed a bit low as well. Then in the last 5 minutes or so of the drive, the problem went away. Any ideas? Thanks in advance.
I also cleaned the MAF meter and the throttle body looked immaculate when I took off the intakes to do the injectors. What is the IAC? Could it be this or maybe a an EGR valve?
 
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Could be a number of things. Do you have any codes?

Chances are disassembly messed up some of the old rubber in your engine. Lots of times intake boots and vacuum hoses crack/break apart on older vehicles. Do a smoke test to see if you have a vacuum leak.

If that's not the case, then start checking your spark plugs and wires.
 
An error code just came up on the dash. I'm gonna drive to the parts store and see what comes up. I changed the plugs and wires, they are new. I did change some rubber hoses that were worn as well when I removed the intakes. It's strange how it's so intermittent.
 
The error code is P0304. It's the #4 cylinder I guess. I changed the coils and plugs and wires. Injectors are rebuilt as well. I looked at the oil dipstick and didn`t see any obvious evidence of a bad head gasket. It's running way rougher now then when I first swapped out these parts. I guess I could move the coil packs around and see if the code changes number?
 
Ggradtech said:
The error code is P0304. It's the #4 cylinder I guess. I changed the coils and plugs and wires. Injectors are rebuilt as well. I looked at the oil dipstick and didn`t see any obvious evidence of a bad head gasket. It's running way rougher now then when I first swapped out these parts. I guess I could move the coil packs around and see if the code changes number?
Click to expand...

When you put the injectors back in, did they all seat correctly, meaning before torquing down the fuel rails did the injectors rotate smoothly? An incorrectly fitted injector can cause leaks, both in fuel or in air.

If a coil pack goes bad, normally you get a code for both sides of the engine, so the coil cylinder and the slave cylinder. Make sure the spark plug boot is not loose, has plenty of grease in the connectors, and has no pinches/damage.
 
I feel confident that I lubed the plug boots/coil connections properly. I also added a small amount of O-ring lube on each end of each injector as well. They seated nicely and almost "clicked" when I installed them. I'm nearly 100% sure it's not injector or fuel related.
Funny thing....... I swapped the NEW coil pack that is the slave to the #4 cylander/spark plug with the OEM original one just to see if the new pack is bad. It ran the same (missing somewhat) with the old OEM coil pack as the new one, so I reinstalled the new one. The 4runner then started with no miss and no engine light!!! What the heck is going on???? Could it be a vacuum leak?
 
Ggradtech said:
So I recently developed a slight miss. Seems to be an issue once the vehicle is warmed up, and doesn't happen when its cold.

I had the original injectors professionally serviced/overhauled/bench tested...
Click to expand...

The coil in the injectors can test in spec when cold and then fail when they get hot. Maybe look at injector resistance on #4 cylinder again using the technique discussed in this thread....

http://www.toyota-4runner.org/3rd-gen-t4rs/234290-maddening-misfire-mystery.html#post2659446

Or swap #4 injector with another cylinder to see if the problem follows it.....

Buckaroo
 
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Maybe you got dielectric grease on the actual metal contact area and changing the coils scraped it off. I cant imagine it would insulate that much though with the pressure of the little spring connector.
 
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Two things to think of. Once a spark plug fouls it can go bad right away and also new parts out of the box don't always work. Start with the fact that you computer is telling you its a misfire on #4. Replace the spark plug for just that cylinder and test If you did not toss out your old wire set take one of the wires that did not have a problem and put it on the #1 coil #4 plug and see what that does. You need to concentrate on that #4 cylinder first, so that would be plug, wire, injector
 
St Runner said:
Two things to think of. Once a spark plug fouls it can go bad right away and also new parts out of the box don't always work. Start with the fact that you computer is telling you its a misfire on #4. Replace the spark plug for just that cylinder and test If you did not toss out your old wire set take one of the wires that did not have a problem and put it on the #1 coil #4 plug and see what that does. You need to concentrate on that #4 cylinder first, so that would be plug, wire, injector
Click to expand...

That's exactly it. Since the injector is the hardest to get to, swapping out the plug would be the easiest thing to do.
 
Ggradtech said:
I feel confident that I lubed the plug boots/coil connections properly. I also added a small amount of O-ring lube on each end of each injector as well. They seated nicely and almost "clicked" when I installed them. I'm nearly 100% sure it's not injector or fuel related.
Funny thing....... I swapped the NEW coil pack that is the slave to the #4 cylander/spark plug with the OEM original one just to see if the new pack is bad. It ran the same (missing somewhat) with the old OEM coil pack as the new one, so I reinstalled the new one. The 4runner then started with no miss and no engine light!!! What the heck is going on???? Could it be a vacuum leak?
Click to expand...

Vacuum leaks show up at a P0171 in most cases, so not likely. Give it some time to see if the issue comes back, like I was mentioning it could have been just a poor connection.
 
Ggradtech said:
So I recently developed a slight miss. Seems to be an issue once the vehicle is warmed up, and doesn't happen when its cold.
As a needed "preventative measure" due to the fact that it has 210k on the clock, I had the original injectors professionally serviced/overhauled/bench tested, new coils, plugs and wires. After this, the 4runner ran much better. I did this work yesterday. Today it ran great when I first drove it for about 30 minutes. I then parked it for about 30 minutes and then when I started it and drove again, the miss came back. It stayed like this with the miss/shuddering for about 30 minutes of driving. Idle seemed a bit low as well. Then in the last 5 minutes or so of the drive, the problem went away. Any ideas? Thanks in advance.
I also cleaned the MAF meter and the throttle body looked immaculate when I took off the intakes to do the injectors. What is the IAC? Could it be this or maybe a an EGR valve?
Click to expand...

I know this is may sound crazy, but did you check the TPS? I have had a few go out on me and they mimic skipping/misfire. Only buy OEM when it comes to this part!
 
Thanks everyone. I kinda threw in the towel so to speak. I have a mechanic friend looking everything over. I'll post back once I hear the outcome.
 
I'm getting so annoyed. I had the mechanic look at the 4runner. At the time of service, it was running perfect. He scanned it and found the #4 misfire code in the history. Since it wasn't showing symptoms at that moment, he couldn't do anything. Today it ran fine for a short drive. I parked it for 45 minutes. It then starting misfiring again when I drove it. What the he'll do I do? Is there a sensor to look at?
 
Putting money on a fuel injector. You need to measure the resistance on it. Should be I think 13.6 ohms. With in that range. If it’s not in the spec. It’s bad injector. And you might not feel it when it’s cold. But once it warms up. It can cause it to misbehave.
 
I'll check all the connections again, but the injectors were completely checked. They did also check the electrical components within each injector. On a side note...... I did a head gasket test tonight. The one that uses a bulb attached to the radiator inlet to check for exhaust gases within the coolant. No issue there, so I'm hopeful it's not a small head gasket leak on cylinder # 4. I also moved coils and wires to new locations to see if the misfire codes " moves" do another cylander.
 
Put a brand new plug in only the #4 cylinder and see what happens. I had this problem with my 97. Got a misfire on #4, it was a bad wire. Replaced the wires with oem and a week later it started to misfire on that same cylinder. Replaced the plugs and it has not had an issue since. The plugs were under 15k and in great shape. Its just that once they misfire and foul they could be no good
 
Did you do a compression test ??...could be mechanical issue...valve or lifter...misfires are normally spark, fuel or compression !!
 
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