Initial cold startup miss

[Nemesis]

Hey guys,

Just thought i'd get some brainstorming ideas off you lot. For a while now, but only occasionally (not every single time,) when i start my 4Runner (petrol V6) it has a slight miss and rough (although still fast @ 1100rpm) idle. And it only lasts for about 2 mins then it's gone. I've recently changed the plugs and leads but it's got me buggered what could cause it.
Also, I don't know if it's related but the V6 has decided to idle at as low as 400 rpm for a while now, I thought these electronic motors don't do things like that.... It still runs fine under a normal load etc.
Any suggestions to either?

[Sea-Dog]

Mate had the same problem in an old falcon he had and it turned out to be a crack in his head gasket letting small amounts of water seep in overnight... the tell tale was that when he started it there seemed to be a bit of a clunk sound associated with the miss.. that was the motor hydaulicing the water in the cylinder.... luckily being a petrol motor it was able to cope with the extra load and didn't do any real damage..

This was a bit hard to track as the oil was clean and there was no bubbles being blown in the radiator either.. just the radiator seemed to slowly go down over a matter of a few weeks.. he originally just thought that was from overtopping when the motor ran at temperature.

May not be the case with your car but I hope it helps.

[Nemesis]

Thanks mate, that sounds interesting. Ironically my radiator level has been dropping, but it's leaking around the thermostat housing. Hopefully it's not leaking where you said aswell.

Jus another thought, could be a problem related to a cold air bypass valve that gives a faster idle untill the motor warms up or an idle speed motor, an easy way to check if this could be your problem is to remove the rubber pipe closest to your throttle butterfly so you can look at the butterfly, then open the throttle with your hand(engine off obviously) and wipe your finger on the other side of the butterfly see if it has heaps of carbon build up on it. If so the idle speed motor and cold start air bypass prob need a clean. They are pretty easy to clean if thats the case

i remember ya sayin the other day at the meet that you had a bit of a problem with low idle...... keep us informed on how ya go

[Nemesis]

Yeah, I stalled going down that rock slide whilst touching the brakes in low 1st as the idle was so low...

[HellRazer]

I agree with tuff toy,idle speed motor.also sounds like an air leak between head and inlet manifold.that will cause a miss and low rough idle when cold,but as the engine warms up and expands it will close the gap and run ok.easiest way to check this is when the engine is cold and running rough,spray some crc,petrol,aerostart or even fly spray along the edges of the inlet manifold and if the engine picks up any revs you have an air leak. ;)

[Redfox]

I agree with tuff toy,idle speed motor.also sounds like an air leak between head and inlet manifold.that will cause a miss and low rough idle when cold,but as the engine warms up and expands it will close the gap and run ok.easiest way to check this is when the engine is cold and running rough,spray some crc,petrol,aerostart or even fly spray along the edges of the inlet manifold and if the engine picks up any revs you have an air leak. ;)


Danger Danger Will Robinson. Definitely DO NOT spray anything flammable on your engine, especially if the misfire is caused by a stray spark from your HT leads. It could really be your nemesis!! Instead spray some water from one of those little pump bottles. It will still do the same thing; ie the engine speed will still change indicating a leak, but it won't blow your head off. Any small amount of water sucked into the engine will do no harm to the engine. Happy hunting, Redfox. 8)

[HellRazer]

I agree with tuff toy,idle speed motor.also sounds like an air leak between head and inlet manifold.that will cause a miss and low rough idle when cold,but as the engine warms up and expands it will close the gap and run ok.easiest way to check this is when the engine is cold and running rough,spray some crc,petrol,aerostart or even fly spray along the edges of the inlet manifold and if the engine picks up any revs you have an air leak. ;)


Danger Danger Will Robinson. Definitely DO NOT spray anything flammable on your engine, especially if the misfire is caused by a stray spark from your HT leads. It could really be your nemesis!! Instead spray some water from one of those little pump bottles. It will still do the same thing; ie the engine speed will still change indicating a leak, but it won't blow your head off. Any small amount of water sucked into the engine will do no harm to the engine. Happy hunting, Redfox. 8)

whatever, will robinson,been doing it for years,if it was a lead it would be a problem all the time not just when cold.

[Redfox]

Another cause may be leaking injectors. They could be leaking fuel into the cylinders when the engine is off. After starting and running for a few minutes the extra fuel is burnt off and it runs pretty much normally. Another symptom, if this is the cause, is longer than normal cranking on cold start up. Redfox :)