"Rough idle during cold start, white smoke"

Hi Guys,

I have been using the forum as a guest for a while now and finally got around to joining the forum as a member. Currently my truck, a 99 prerunner, will have a rough idle and spit white smoke from the exhaust, however after the first few minutes everything is fine and the truck will be good to go the whole week with no loss of power or overheating. If it sits for an extended period of time (the weekend) the same thing will happen; white smoke, rough idle . I have seen that it may be a bad head gasket and I have done some of the tests: no bubbles from radiator, oil looks normal, no loss of radiator fluid. I am out of ideas for what to test because it seems to have the symptoms of a bad head gasket but none of the "quick test" show that it is bad. Let me know what I can do to test if further or if you think it may be something else.

Thanks

 

If you put a pencil mark on the overflow/expansion tank when cold, and over several weeks fluid is still at that mark when cold, then you are ok as far as coolant loss.

 

I'd start with a compression test on each cylinder.

 

I'm no expert but i have rough idle whenever Im stopped at a light or in traffic. I just bought this stuff called sea foam. i plan on putting it in my vacuum line, crankcase, and fuel system. do some research on it. my rough idle isn't only on cold start though. There is for sure white smoke? cause a lot of cars when its cold have moisture in the exhaust and its just water evaporating cause of all the heat in the exhaust system. and is the rough idle super noticeable or its very light and pretty much only you can notice it?

 

I never thought to use sea foam until now. It runs rough for only the first 3 -5 min. The smoke is during that rough idle and doesn't seem like it would be moisture in the exhaust. After the rough idle it is perfectly fine like nothing happened and there is no more white smoke. It only seems to happen on Mondays when my truck sits for the weekend or hasn't run for a few days. The rough idle is super noticeable. I figured it would run rough all the time and smoke more if there was in fact a blown head gasket.

 

ill look it up in my chilton when i get home to see if there is anything about cold starts or smoke out of the exhaust. ill also let you know how the sea foaming goes. i agree about the blown head gasket.. Seeing as it runs fine 99% of the time its probably nothing serious. (thats what the dealership said to me). have u driven it while it runs rough? is it rough when you step on the gas pedal? Mine goes away as soon as you put your foot on the gas pedal.

Edit: my truck used to misfire before my valve job (and the CEL wouldn't come on) but it would still have a code if u plug the scanner in. so if you have any buddies with a OBD2 scanner you might wanna borrow it one monday morning and check it out.

 

The only thing that would cause smoke would be oil leaking into the cylinders, which could happen (check for any oil consumption). More than likely it's water vapor. Have you looked at the idle air control valve to see if it's functioning properly? When the engine is cold, it should be using more fuel and a little more air until it warms up. If its not getting one or the other, it could cause a rough idle. You might also want to clean the throttle body just to make sure it's closing properly.

 

I cleaned my throttle body and iac and it definitely made a huge improvement to my rough idle problem. I did clean a 1/4" thick glob of carbon build up right behind the throttle body(in the begining of the intake manifold). Make sure u do it on a weekend so you have a few days to get your truck back together. YouTube has a few videos that will help with the iac cleaning. Careful not to over tighten the throttle body bolts.

 

What would cause oil to leak into the cylinder? I will try check everything you suggested.

 

If the valve stem seals are worn, oil could run down the valve into the cylinder. I'm not sure which engine you have (4 or 6) but a tiny bit of oil down enough valves while sitting and it could be visible when you restart it. That's why I suggested checking your oil consumption. Of course, this only works if you don't have any external oil leaks because we're talking tiny little amounts of oil.

Edit: Here's a link to a totally different vehicle and engine but it has some good pictures of valve stems with the seals in place and removed. You can see how the oil could seep down along the valves as it sits for a few days: http://www.team-integra.net/forum/b...323-how-install-valvesprings-valve-seals.html

 

Well used the sea foam. The first time I did it it was alright. But I did it a second time right after (I don't suggest doing this). When I started it back up 30-50 minutes later it almost didn't start I stepped on the gas and it putted to a start. Phew soooo much smoke came out literally filled the entire street I had to go around the block a few times but after it made my idle really smooth.