My 1996 5 speed 250,000 4runner starts perfect but developed a rough idle for 30 seconds for 3 months. Twice in 2 months it belew white smoke very thick for a mile, then totally quits? Never had cleaned the radiator but now I did and it was low and possibly contaminated or mix of green and red antifreeze over the years per the mechanic who put in plugs, timing belt, water pump as a overdue prevention. Mechanic said my compression was 185 on all cylinders, but one at 160? So I put radiator flush in it, ran it for 300 miles, drained it, filled it with fresh antifreeze, drove it 400 miles and this morn again it blew white smoke only with the truck accelerating, let off the peddle and obviously smoke went away. 1 mile from home, ran perfect again. Started tonight to come home, totally perfect, but was 1/2 quart low on water since the 400 mile antifreeze change. Has me baffled. I see many posts on the white smoke issue, but no one with a fix? Wouldn't a blown head gasket be constant? Not a month apart?

Assuming the truck isn't in bitter cold temperatures, and you aren't just seeing steam from condensation out of the tailpipe as the exhaust system warms up, (I don't think that's the case as the initial rough idle after sitting is a clue) it sounds like a headgasket that's developed a leak and is allowing coolant into a combustion chamber.

Keep driving it and it will get worse.

I would fix it before you do real damage like cracking the heads and warping the block deck. Those can be fixed too, but it drives the cost up.

Another thing, if your Mechanic isn't astute enough to diagnose a leaking headgasket, I'd find someone competent to replace it.

Sorry if the Mechanic is someone you know, but sugarcoating the answer I think would be a disservice to you.

No washed out plugs? 1/2 quart over 400 miles isn't much, especially right after a coolant flush. The system can and will purge air pockets that remained after the system was bled.

Could be a leaking head gasket, could be a cracked head too. As the motor warms up things expand and swell, which could be sealing the leak or crack. As the motor cools, coolant seeps through into the cylinder again, causing the rough start and white smoke.

sounds like bad valve seals to me.

Some posts say the miss could be a weak fuel pump to not pump enough gas while cold choking?
1. Some state it can be a plugged fuel filter as mine in 260,000 has never been changed?
When the mechanic changed the plugs, the day I go it back and a few days after it started perfect. Now it shakes again. So process of elimination says to find from him which cylinder was the low one and pull that plug for inspection?
2. If water is leaking from a head gasket to that plug, what should I notice?
3. To blow this 1 mile billow of white smoke, 1 month apart and 1000 miles apart just seems odd? If something was sticking open or closed, what could the thremostat be doing to cause water problems? Reason I ask is that when I did change the radiator flush we let it sit cold at 20 degrees out side and it blew cold air for a long time at idle, to get it to turn hot, I put the 4Runner in gear and began to drive out of the driveway and all of a sudden (and this happend twice while flushing) it went hot ASAP as it triggered the thremstat to respond.
I've never noticed this before if warming in my garage? But then again I normally jump in and take off to warm it up.
Thank you all for your help and replies truly as it is a puzzle to me.

How ever the cold engine choke works, I am guessing the engine is running rich at start up sometimes as it is not consistent for the first 30 seconds and once I start off and the miss quits, I am burning gas vs steam, for the first block. Last few days, no smoke but little or No miss at startup. And radiator is full.
What is the unit called that chokes the engine? Or if it is just choking the one piston that is 150 PSI?

I have similar problems and hopefully you fix it

During a cold start the engine desired air fuel ratio. Starts out around 8:1. Really rich and needed for warmup. That requires a lot of extra fuel flow compared to the 14.7:1 ratio after warmup cycle is complete.


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I don't think the OP in 3+ years is still driving around with a bad head gasket.

If one sees white smoke, coolant is going somewhere it shouldn't. A block test, compression and leak down test should be performed.

I have just been having the exact same symptoms. Whitish smoke or steam on and off suddenly stopping for days then back again, short misfires on cold start ups etc... this week I had worse bubbling in the overflow tank than ever, that pretty much told me it was the HG going bad.

Last night I finally resorted to using that new Prestone triple protection block seal stuff. Today I have zero white smoke/steam except the usual cold start steam. Zero bubbling in the over flow tank and a perfect cold start up ! Looks like it's fixed, just for how long though !!

I had some similar issues, and it was a dirty fuel injector that was getting stuck open. While the truck sat it would allow some of the remaining fuel in the fuel rail to drain down into the intake. It wouldn't happen all of the time. If something happened it tended to be just a few second of running rough, and sometimes I'd get some white smoke.

Had my mechanic run some fuel injector cleaner through it, and it hasn't had that problem since.

I'd still like to pull my fuel injectors and send them out to get cleaned and tested properly.. I'll still get a tiny bit of a rough idle sometimes.

Did the product hold up so far??

I think he gave up and sold it.