: Why does dirty TB cause crazy idle?



csbacchus
09-20-05, 12:02 AM
I'm a newb here, just wanted to thank everybody first of all for all the information being shared.

It was this forum that convinced me to go ahead and buy a 1995 STS :cool2: with 82,000. Mechanic went through it and didn't find a thing wrong except the usual fluid changes, filters, etc (Not even an oil leak!). However, 2 days later I develop this crazy idle that goes from 1200-1500 all the way to 3000. It was a google search that led me to the archives and hours of hunting through threads I found many references to cleaning the throttle body first and then working your way to the ISC. I found a TB which looked like it had been treated with a black lacquer. I've cleaned about 50% and will continue to work on it (it is really solid, like nail polish almost). It seems to have done the trick on the idle though.

However, can anyone tell me why this causes the high idling? I'm curious by nature.

Also, I cleaned the MAF with contact cleaner, a little trick I learned when I had my F-150. There is rarely a need to replace this item since it only gets dirty and there aren't any moving parts.

Thanks again, I really appreciate all the info.

I love this ride! :lildevil:

danbuc
09-20-05, 12:26 AM
A gummed up TB or IAC motor can cause an unstable idle because they get stuck, and don't fully close. The IAC motor openes and closes the the throttle plate many times a second to keep the idle steady. When this goes bad, the idle can rise and fall in a rather unpredictable manner, because the IAC can regulate it. Also, if the Throttle Plate gets gummed up with carbon or what have you, it won't fully close all of the way, resulting in a higher idle.

On a side note, you 1995 STS shouldn't have an MAF being OBDI. It should have a MAP sensor though. I would also be careful with spraying contact cleaner on MAF sensors in general. Some are hotwire MAF sensor which are actually self cleaning. They heat up to abotu 1200 degrees fahrenheit for a fraction of a second to burn off any contaminents. Spraying contact cleaner on them could cause damage.

csbacchus
09-20-05, 12:50 AM
Thanks for the head's up Danbuc.

You're probably right on the sensor, I really need to get a shop manual for this thing. Since it was in relatively the same area of the intake I just went with the sensor I was familiar with.

By the way, I'm using seafoam on the TB. Anything work better? This stuff is much worse than the TB on my F-150 and it had more miles on it when I cleaned it.

danbuc
09-20-05, 01:15 AM
Seafoam in fine. You might want to get an old toothbruch, and get some TB cleaner and spray it on there. That will help scrub some of the caked on stuff off of there. If the sensor that you clean was like a small two wire thermistor mounted in the side of the intake hose, that just the Intake Air Temperature sensor, which is fine.

Ranger
09-20-05, 11:53 AM
I have never used Seafoam so I can't comment on it but good old fasioned Gumout carb cleaner (yeah I still have some) works great.

eldorado1
09-20-05, 12:42 PM
Seafoam doesn't do crap, despite what the folks behind the counter will say.

Get some carb/TB/whatever cleaner, and spray it, and be done in 5 minutes. Guaranteed or your money back.

mcowden
09-20-05, 12:57 PM
Seafoam doesn't do crap, despite what the folks behind the counter will say.

Get some carb/TB/whatever cleaner, and spray it, and be done in 5 minutes. Guaranteed or your money back.

I have to agree with eldorado1. I can't speak to the merits of SeaFoam in applications like a crankcase solvent or injector cleaner, but as a throttle body cleaner, it's really not that good. I've used SeaFoam, Chevron fuel injector cleaner, and carb cleaner to clean throttle bodies, and the carb or brake cleaner works best by a long shot.

SeaFoam is basically a mix of kerosene, alcohol, and mineral spirits. Those are all decent solvents, but there are other solvents that work better for the kind of crud that will accumulate on a throttle body. Whether or not SeaFoam really works well as an injector cleaner or crankcase sludge dissolver, I don't know for fact, but it would seem that straight kerosene or other solvents and detergents would work cheaper and/or better.

csbacchus
09-23-05, 06:51 PM
Thanks for all the info on other cleaners. I'll pick something else up and either send this Seafoam in for a refund or just use it for something else.

mcowden
09-23-05, 11:09 PM
Thanks for all the info on other cleaners. I'll pick something else up and either send this Seafoam in for a refund or just use it for something else.

The Seafoam will work, it just takes longer to get the job done. If you use something else, dump the Seafoam in the gas tank before you fill it up one of these times, or idle the engine, pop off the brake booster hose, and VERY SLOWLY pour it into the hose. When you see lots of exhaust smoke, turn it off. Let it sit for 10-15 minutes, then start it up again and drive it for 5-10 minutes until the smoke goes away. That'll help clean the intake and valves a bit. I usually use Chevron with Techron fuel injector cleaner for that job, but the Seafoam should also serve as an OK top engine cleaner. Just make sure you put that brake booster line back on there, and don't pour it in there too fast or you could hydrolock the engine and bend a rod or worse.

eldorado1
09-24-05, 12:36 PM
Just make sure you put that brake booster line back on there, and don't pour it in there too fast or you could hydrolock the engine and bend a rod or worse.

The trick seems to be not raising the RPM above 2000 after you've emptied the bottle. Because now you've got a 16oz puddle on the bottom of your intake, and to get ingested into the engine, it has to rise up 6" into the intake runners. 2000rpm will do this at a moderate rate. Any higher and it will start to slurp the puddle.