Rough idle/misfire when cold until warm - Re-Solved - HG

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PeterTheBeater

PeterTheBeater

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Jan 11, 2019
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Sacramento
Got a 97 FJZ80.

Got a weird issue where under cold start, it idles very roughly for the first 30 seconds or so. No check engine light, full tune up (plugs, rotor, etc) was done about two years ago, including all vacuum lines (valve seals replaced) and filters. Don’t see anything out of ordinary under the hood, issue started randomly.

Thanks
 
PeterTheBeater said:
Got a 97 FJZ80.

Got a weird issue where under cold start, it idles very roughly for the first 30 seconds or so. No check engine light, full tune up (plugs, rotor, etc) was done about two years ago, including all vacuum lines (valve seals replaced) and filters. Don’t see anything out of ordinary under the hood, issue started randomly.

Thanks
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Same here. Just did injectors too. Seams to do it after its hot. I also moved the EFI relay inside the cab and heat shielded the entire wiring harness for it. I also just heat wrapped a large section of the harness that goes around the intake manifold. Gonna see if that helps. Might be vapor lock. I've done a full engine restore and complete fuel system restoration.
 
Can't be a vapor lock; you don't have a carburetor.
 
try removing the throttle body and giving it a good clean. On warm up the IAC plays a decent part in keeping things running smooth and if its sticky or built up with carbon ./ crud will cause erratic / rough idle. The back of the throttle plate also if not sealing right will affect idle smoothness

either way, periodically removing / cleaning the throttle body is a good thing
 
Going to take the throttle body off and clean it. I did do a deep clean two years ago with all the vacuum lines, so I doubt that will fix the issue.

It definitely feels like a misfire when it first starts up and then clears out smooth. I think it might be a head gasket because it runs super smooth and idles great once warmed up a little bit.
 
PeterTheBeater said:
Going to take the throttle body off and clean it. I did do a deep clean two years ago with all the vacuum lines, so I doubt that will fix the issue.

It definitely feels like a misfire when it first starts up and then clears out smooth. I think it might be a head gasket because it runs super smooth and idles great once warmed up a little bit.
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if youre running red OEM coolant I'd remove the spark plugs when stone cold and have a good look. any HG issue may show up as a reddish tinge on the plug

hopefully its not.....
 
Pulled off the throttle body and the EGR, is it a little dirty and wet - yeah,

Is it enough to do anything? IMO - no

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robnicko said:
if youre running red OEM coolant I'd remove the spark plugs when stone cold and have a good look. any HG issue may show up as a reddish tinge on the plug

hopefully its not.....
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It wasn’t stone cold, but pretty cold. I had this issue happen for few weeks now, so I think it would have shown. Pulled all the plugs and looked down the cylinders, they look about the same. Cyl #6 has soot in it just like the others ones, I think if it was a HG it would be shiny and clean.
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plugs all look fine to me.

as for the EGR I cant comment as i'm fortunate enough to not have one on my 80.

inside the intake manifold the wetness, is that oil or fuel over carbon?
check near the oil filter that the coolant temp sensor is connected properly, could be a case of extreme rich running until it gets to temp. I believe there is a second sensor near the thermostat housing as well. one does the dash gauge the other the ECM
 
robnicko said:
plugs all look fine to me.

as for the EGR I cant comment as i'm fortunate enough to not have one on my 80.

inside the intake manifold the wetness, is that oil or fuel over carbon?
check near the oil filter that the coolant temp sensor is connected properly, could be a case of extreme rich running until it gets to temp. I believe there is a second sensor near the thermostat housing as well. one does the dash gauge the other the ECM
Click to expand...
It’s the oil, my PCV valve is super wet.

ECM Coolant temp sensor is actually new as well, was replaced when I did the valves seals.

One thing I forgot to mention, cyl 5 plug was not even snug, like I could break loose with my hand.

I buttoned everything up and it started up fine, no miss during idle. I’m going to try again tomorrow morning and see how it does, it was very consistent in the misfire.

One hypothesis is it was low on compression or the plug wasn’t properly grounded by being loose, until it warmed up and expanded? I don’t know, in general it’s VERY weird for a plug to be loose like that (they were all torqued to spec). Also I didn’t really hear any engine compression sounds and the spark plug boot was still sealed.
 
Well this is now back to unsolved. The “misfire” is still there when the engine starts for the first 10-15seconds, but it is much better than it was before. Can still feel it but it doesn’t shake. I replaced the O2 sensors for fun due to previous codes but that didn’t do anything. P0401 still popped up once. I don’t think it’s related to IAC because it’s only on start up under 30 seconds, and the rpm doesn’t hunt like it usually does under IAC issue.
 
I'm still wondering about whether this can be an incipient head gasket issue... My HG started to fail exactly like you describe, with an intermittent cold start rough idle for 15 sec or so. In my case. compression tests were ok, and no exhaust gases were detected in the coolant. But the giveaway in my case was a slight drop in coolant level over time. Like a week... It was very slight. What was happening was that as the engine cooled, a tiny amount of coolant was being drawn into cylinder number 5 and it then ran rough until cleared on subsequent start up. It was like that a while until I got fed up enough with it to pull the head off to find a deteriorated original HG. I then got into a 'while you are in there' rebuild but that's a different story. I hope that's not your case but may be worth keeping in back of mind as you trouble shoot. Definitely worth a very close eye on coolant levels over time, which is an easy check.
 
Did a cold compression test this morning, starting 1 to 6

170-175psi
165-170psi
170-175psi
165-170psi
175-180psi
175-180psi

So yes, I guess cyl 2 and 4 are lower in compression but IMO not enough to show a leaking HG. Plus this is cold, when its warmed up they'll all be above FSM at 171.

Not sure what to do besides throwing parts or finding a toyota scantool to do FSM troubleshooting

I did test my EGR temp sensor and it says OL, looks a new one is 150$ !!!! Well I boiled some water and it read 20kOhm, so at least it works kinda.

IAC valve resistance is all 20-21ohm

EDIT: followed EC11 and hooked up EGR to intake, expected engine to die but it did not change how it ran.
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