Slight Misfire/Shake at Idle After Head Gasket Job

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EPIC Cruisers

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Hello everyone,

Since I got my LX back from the shop that did my head gasket job I have noticed that it has, what I would consider, a slight misfire/shake at idle. Or at least that's what it feels like. It only happens at idle when in Park or at idle while in Drive. It's definitely not a constant thing, but it is consistent in that the shake/misfire happens about every 10-15 of seconds at idle. Otherwise the LX runs great while actually driving. At first I thought maybe everything needed to "wear in" and that it would go away in a couple hundred miles but I still have no change.

I'm sure the shop will take another look at it but I wanted to try and resolve this issue before having to go back to them. Mainly because it would save me a lot of time since they're about an hour away and I'd have to get someone to give me a ride back, etc.

During the head gasket job everything coolant system related was replaced, except for the clutch fan. The head was fully serviced as well. The injectors were sent out to be cleaned and flow matched. New injector connectors were installed. A new fuel filter was installed. We also replaced a the VSV and vacuum check valve under the manifold. I had also already replaced the vacuum hoses, PCV valve/hose, spark plugs, wires, rotor button, and distributor cap before they worked on it. All OEM Toyota parts.

Since getting it back I have installed the VC120 charcoal canister (I had the tank venting to atmosphere and the hose going to the manifold plugged previously). I have replaced the intake boot with an OEM Toyota one. Replaced the cat/Y-pipe with a Magnaflow and both oxygen sensors with Denso ones (was initially going to only replace the sensors but saw that my OEM Y-pipe had almost rusted through on the oxygen sensor mount). I even tried putting my old spark plugs, rotor button, and distributor cap back on.

However after all this I have no change whatsoever and I am completely stumped as to what the issue could be. Anyone have any possible ideas?
 
What about the ignition coil? Did you replace that as well?

No, that hasn't been replaced. I didn't have any issues with the ignition system before the head gasket blew. I only replaced most of the ignition system as preventative maintenance. Do you think that could possibly be the issue? I guess that would explain why it only happens at idle and not while under load.
 
What about the ignition coil? Did you replace that as well?

No, that hasn't been replaced. I didn't have any issues with the ignition system before the head gasket blew. I only replaced most of the ignition system as preventative maintenance. Do you think that could possibly be the issue? I guess that would explain why it only happens at idle and not while
 
Check the various vacuum lines. The ends develop cracks as the rubber ages. Even possible one was missed and just dangling? You may need to clip the ends of a few hoses and reinstall if they look cracked, etc. All the on/off of work like this will bring this up. If they look generally good, inspect as best you can, then try running it to see if the issue is resolved. If not, then move on to the next possibility.
 
My thought is it sounds ignition related and you replaced everything else in the ignition system so that could be it. Or like green truck said could be vacuum related since it's at idle.
 
Check the various vacuum lines. The ends develop cracks as the rubber ages. Even possible one was missed and just dangling? You may need to clip the ends of a few hoses and reinstall if they look cracked, etc. All the on/off of work like this will bring this up. If they look generally good, inspect as best you can, then try running it to see if the issue is resolved. If not, then move on to the next possibility.

I actually replaced the vacuum lines before the head gasket job. Everything seems like it's hooked up correctly but I'll definitely check them again.

My thought is it sounds ignition related and you replaced everything else in the ignition system so that could be it. Or like green truck said could be vacuum related since it's at idle.

I'll look into ordering a new one. It definitely won't hurt to replace it, if anything it'll be preventative maintenance as well.
 
I noticed something similar after doing all of the same work you did and I found that switching to no ethanol gas has cleared mine up entirely. Not sure it's your issue, but it might be worth a shot.
 
I noticed something similar after doing all of the same work you did and I found that switching to no ethanol gas has cleared mine up entirely. Not sure it's your issue, but it might be worth a shot.

I actually am already running 89 octane non-ethanol gas currently. I fill up at the same gas station in town every time. I'm a little too stringent about it. lol

Do you have a supercharger?

I don't, I wish I did though. Haha
 
How many miles since the work was performed? How about spark plugs? Check it with a vacuum gauge if it's a non VVT engine.
Forget about the VVT part I misread.
 
How many miles since the work was performed? How about spark plugs? Check it with a vacuum gauge if it's a non VVT engine.
Forget about the VVT part I misread.

Less than 400 miles. Sparkplugs seemed fine, I even swapped them for the old ones I took out. It didn't make a difference though. I have the stock 1FZ-FE, is there something I can follow in the service manual?
 
I actually am already running 89 octane non-ethanol gas currently. I fill up at the same gas station in town every time. I'm a little too stringent about it. lol



I don't, I wish I did though. Haha

Some of the SC folks have noticed a similar symptom. Best guess is/was that it runs a tad bit lean at idle due to running at 18/20 # of vacuum at idle?
 
Some of the SC folks have noticed a similar symptom. Best guess is/was that it runs a tad bit lean at idle due to running at 18/20 # of vacuum at idle?

Maybe, the only thing is that before the head gasket blew I didn't have this issue. That's what's confusing me so much about this. You would think it would run better now after all this work (which it does besides this small issue).
 
Less than 400 miles. Sparkplugs seemed fine, I even swapped them for the old ones I took out. It didn't make a difference though. I have the stock 1FZ-FE, is there something I can follow in the service manual?

I would hook up a vacuum gauge and see what the gauge is indicating, did they do a complete valve job? Check valve clearance when cold and hot. I had a bad experience with my 3.4l when I bought it from a rebuilder and it had a miss from the first day I installed it later on I found out
that the valves were cut too thin and the guides were all worn out it last 20k miles before it failed. The vacuum gauge is a good indicator for any mechanical issues.
 
I would hook up a vacuum gauge and see what the gauge is indicating, did they do a complete valve job? Check valve clearance when cold and hot. I had a bad experience with my 3.4l when I bought it from a rebuilder and it had a miss from the first day I installed it later on I found out
that the valves were cut too thin and the guides were all worn out it last 20k miles before it failed. The vacuum gauge is a good indicator for any mechanical issues.

Yes, a valve job was completed. Where/how should I hook up the vacuum gauge? Or will anywhere work?
 
While making sure that all the vacuum lines were hooked up correctly I discovered this...

IMG951882.webp
 
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