Fluctuating Idle

[Tom C]

This is the support topic for the DIY Tutorial Fluctuating Idle. Please post here if you have any questions or feedback.

Edited February 20, 2010 by Tom C

[fasterjames]

How many miles on it? Is it a wondering or rolling idle change?

Could be several things but here are a few things you'll see in several posts that potentially could be causing it: A/C just happens to cycle on/off at that time, throttle body needing to be cleaned, MAF in the very beginning stages of needing cleaning or replcement, clogged air filter, etc.

[Loren]

Sounds like it needs the throttle body cleaned.

[Tom C]

How many miles on it? Is it a wondering or rolling idle change?

Could be several things but here are a few things you'll see in several posts that potentially could be causing it: A/C just happens to cycle on/off at that time, throttle body needing to be cleaned, MAF in the very beginning stages of needing cleaning or replcement, clogged air filter, etc.

I have 44,000 miles, the fluctuation is rolling and does so with or without the AC on. The air filter is new, what is the MAF?

[Loren]

It is not the MAF - the MAF does nothing at idle.

Chancers are you have a carbon buildup around the throttle butterfly. On egas cars there is no idle control valve like the older cars - instead the throttle butterfly is opened just slightly to maintain and control the idle. If you look at the pic I posted above - that is Tariq's car and he had exactly the same problem. On the outside if you look at that throttle body it does not look to bad. But if you push the throttle butterfly open you would see carbon buildup all around the butterfly seating surfaces. Once we cleaned this off his idle was rock stable.

You could try some Techron in the gas but the best short term fix is to clean the throttle body with some spray card/fuel injector cleaner (keep it off the paint). You will need to push the butterfly open with your finger to clean inside. Let it dry for a few minutes then start the car.

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

[Tom C]

It is not the MAF - the MAF does nothing at idle.

Chancers are you have a carbon buildup around the throttle butterfly. On egas cars there is no idle control valve like the older cars - instead the throttle butterfly is opened just slightly to maintain and control the idle. If you look at the pic I posted above - that is Tariq's car and he had exactly the same problem. On the outside if you look at that throttle body it does not look to bad. But if you push the throttle butterfly open you would see carbon buildup all around the butterfly seating surfaces. Once we cleaned this off his idle was rock stable.

You could try some Techron in the gas but the best short term fix is to clean the throttle body with some spray card/fuel injector cleaner (keep it off the paint). You will need to push the butterfly open with your finger to clean inside. Let it dry for a few minutes then start the car.

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

Thanks, I'll clean it tonight.

[chaser]

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

Are you using the 12oz. bottle of Techron?

[Loren]

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

Are you using the 12oz. bottle of Techron?

I use a 16 oz. bottle (you made me look :lol: ).

I also put it in - not with a full tank but when the tank is less than half full.

[chaser]

Are you using the 12oz. bottle of Techron?

I use a 16 oz. bottle (you made me look :lol: ).

I also put it in - not with a full tank but when the tank is less than half full.

Thanks for looking.

I agree with when you add the Techron. When you now fill your gas tank it mixes the Techron properly.

[Tom C]

It is not the MAF - then MAF does nothing at idle.

Chancers are you have a carbon buildup around the throttle butterfly. On egas cars there is no idle control valve like the older cars - instead the throttle butterfly is opened just slightly to maintain and control the idle. If you look at the pic I posted above - that is Tariq's car and he had exactly the same problem. On the outside if you look at that throttle body it does not look to bad. But if you push the throttle butterfly open you would see carbon buildup all around the butterfly seating surfaces. Once we cleaned this off his idle was rock stable.

You could try some Techron in the gas but the best short term fix is to clean the throttle body with some spray card/fuel injector cleaner (keep it off the paint). You will need to push the butterfly open with your finger to clean inside. Let it dry for a few minutes then start the car.

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

Thanks, I'll clean it tonight.

:D

Thanks for your help Loren; I removed the large air duct that runs from the air cleaner box to the throttle body. I couldn't get to the bolts on the bottom to completely remove the body but was able to clean by spaying carb cleaner into it while the body was still on the engine. It cleared the problem and now she idles at a nice 650 rpms!

By the way is there a trick to getting the airline back on the throttle body? I finally got it back on but it was really tough. I greased the lip of the throttle body and then had to heat the duct with a heat gun, keeping it well away from the engine due to gas vapors and it finally set in. There has to be a better way.

[Loren]

:clapping: I thought so.

Both the throttle body and tube should be clean and free from dirt or grease (grease attracts dirt).

I usually just put both hands around it and move it back and forth until I get one (barely) side started - then push straight on.

[blue2000s]

When I took the throttle body off the car, I noticed that the butterfly is not completely closed in it's neutral position (signals completely disconnected). It can easily be completely closed if you push on it with your finger but it springs back to slightly open. I assume that's the starting position to maintain idle but I've never seen that in other cars before.

Edited June 26, 2007 by blue2000s

[Loren]

On an egas car that is normal. The DME will adjust it depending on temperature, air flow, etc. , etc..

[Tom C]

:clapping: I thought so.

Both the throttle body and tube should be clean and free from dirt or grease (grease attracts dirt).

I usually just put both hands around it and move it back and forth until I get one (barely) side started - then push straight on.

You must be built like your governor!!

Thanks again.

[Daryl80]

Hi All

May I ask, what exactly is a throttle body cleaner? I'm located in Australia, and unfortunately, CRC doesn't stock the throttle body cleaners locally. I seem to have similar symptoms, but is there a more generic term for the cleaner?

Thanks for your help

[Loren]

Carburator cleaner , fuel injector cleaner, etc. A spray can version will be easier to use.

Most of these contain primarily lacquer thinner so keep them away from any painted surfaces.

[Daryl80]

Hi Loren

Thank you for your help. Bought some carb cleaner in a can and was all set to clean the throttle body. This was the first time I ever opened up the engine compartment, and ****, was it dirty! Everything was covered in a grimy soot, so I would not be surprised to find the throttle body completely clogged up.

The only thing is now, I have no idea what I'm looking for. I've kind of traced where I think the air box would be, and i can see a thick pipe that leads to the centre of the engine. (between the parts that read's Porsche) I'm guessing this is the throttle body. Is it? I'll try to get my camera to take a photo, but if this is the throttle body, how on earth do I get to it? There are cables on top, other pipes.

Sorry for my ignorance, I'm not really engine literate, so if there is a DIY guide, I would definitely appreciate it.

Thank you all

ps, I've done a search, but sorry couldnt find anything

[Glyn]

As an alternative to a propriety cleaning fluid you can use brake fluid, a great cleaner on throtle deposits just dont get it on any paintwork - it will soften, blister and remove the paint.

When i worked for British leyland (BLMC in those days) brake fluid was generally regarded as the top product for cleaning carbs

[uabchris]

It is not the MAF - then MAF does nothing at idle.

Chancers are you have a carbon buildup around the throttle butterfly. On egas cars there is no idle control valve like the older cars - instead the throttle butterfly is opened just slightly to maintain and control the idle. If you look at the pic I posted above - that is Tariq's car and he had exactly the same problem. On the outside if you look at that throttle body it does not look to bad. But if you push the throttle butterfly open you would see carbon buildup all around the butterfly seating surfaces. Once we cleaned this off his idle was rock stable.

You could try some Techron in the gas but the best short term fix is to clean the throttle body with some spray card/fuel injector cleaner (keep it off the paint). You will need to push the butterfly open with your finger to clean inside. Let it dry for a few minutes then start the car.

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

Thanks, I'll clean it tonight.

:D

Thanks for your help Loren; I removed the large air duct that runs from the air cleaner box to the throttle body. I couldn't get to the bolts on the bottom to completely remove the body but was able to clean by spaying carb cleaner into it while the body was still on the engine. It cleared the problem and now she idles at a nice 650 rpms!

By the way is there a trick to getting the airline back on the throttle body? I finally got it back on but it was really tough. I greased the lip of the throttle body and then had to heat the duct with a heat gun, keeping it well away from the engine due to gas vapors and it finally set in. There has to be a better way.

Hi TomC.

After reading your post I decided to clean my TB too. I also had problems trying to get the intake tube offf of the TB so I also removed the tube from the air box and removal/installation was a snap! I think the pipe is so rigid it is best to remove both ends....Mine was DIRTY!!! Chris

[Tool Pants]

Daryl80. In a prior post you said you have a 1997. Yellow arrow is to the idle control valve on my 1997. It is held in place to the throttle body with 2 bolts.

I have not tried to do this on a Boxster whith the throttle body still connected. So give it a try and see if it works.

Remove the 2 screws and the valve if there is room to do it this way. There is a round thing inside that is supposed to rotate. That thing stabilizes the idle. When carbon gets on it it does not rotate smoothly. Clean it.

[Daryl80]

Hi Tool Pants

Thanks for your reply and picture. Firstly compared to mine, your engine is spotless!

But yes correct I do have a 1997. I've taken your photo, so can I confirm a few things. Can you please confirm that the item circled in red is the throttle body. Is that correct? In regards to the idle control valve, do I need to remove the tubes as marked in green, to get to it?

To be honest, I thought I had to remove the pipe that comes from the airbox into the throttle body and was expecting to need to get into the butterfly valve. Is this not needed for a 97 Boxster?

Thanks again. I'll give it a go with the two bolts, but please to everyone else, keen to hear if you have any more advice.

[Loren]

...and don't break or lose the paper gasket that goes between the idle control valve and the throttle body.

[azzar0]

Hi Tool Pants

Thanks for your reply and picture. Firstly compared to mine, your engine is spotless!

But yes correct I do have a 1997. I've taken your photo, so can I confirm a few things. Can you please confirm that the item circled in red is the throttle body. Is that correct? In regards to the idle control valve, do I need to remove the tubes as marked in green, to get to it?

To be honest, I thought I had to remove the pipe that comes from the airbox into the throttle body and was expecting to need to get into the butterfly valve. Is this not needed for a 97 Boxster?

Thanks again. I'll give it a go with the two bolts, but please to everyone else, keen to hear if you have any more advice.

Is there a way to clean the engine? Mine is extremely dusty and wiping it doesn't really get it clean.

Tool Pants, is the procedure you described valid for a MY98 as well or is the placement of the throttle body different?

Thanks,

Azzar0

[Tool Pants]

The red oval is the throttle body. 1997-1999 is non-egas. You can see the throttle cable in the picture.

I was trying to keep it simple if there is room to remove just the idle valve from throttle body. Have not tried to do it this way on a Boxster, but it can be done this way on a non-egas 996. To clean inside the throttle body itself you need to remove the large tube that comes from the air box.

[Tom C]

It is not the MAF - then MAF does nothing at idle.

Chancers are you have a carbon buildup around the throttle butterfly. On egas cars there is no idle control valve like the older cars - instead the throttle butterfly is opened just slightly to maintain and control the idle. If you look at the pic I posted above - that is Tariq's car and he had exactly the same problem. On the outside if you look at that throttle body it does not look to bad. But if you push the throttle butterfly open you would see carbon buildup all around the butterfly seating surfaces. Once we cleaned this off his idle was rock stable.

You could try some Techron in the gas but the best short term fix is to clean the throttle body with some spray card/fuel injector cleaner (keep it off the paint). You will need to push the butterfly open with your finger to clean inside. Let it dry for a few minutes then start the car.

I find a bottle of Techron every 3000 miles or really helps prevent the buildup.

Thanks, I'll clean it tonight.

:D

Thanks for your help Loren; I removed the large air duct that runs from the air cleaner box to the throttle body. I couldn't get to the bolts on the bottom to completely remove the body but was able to clean by spaying carb cleaner into it while the body was still on the engine. It cleared the problem and now she idles at a nice 650 rpms!

By the way is there a trick to getting the airline back on the throttle body? I finally got it back on but it was really tough. I greased the lip of the throttle body and then had to heat the duct with a heat gun, keeping it well away from the engine due to gas vapors and it finally set in. There has to be a better way.

Hi TomC.

After reading your post I decided to clean my TB too. I also had problems trying to get the intake tube offf of the TB so I also removed the tube from the air box and removal/installation was a snap! I think the pipe is so rigid it is best to remove both ends....Mine was DIRTY!!! Chris

We both owe Loren a steak dinner where ever you are. If you're ever in West New Jersey let me know, I'm buying!