One of the problems that I see with many 996/986/997/987 owners complaining about is a lumpy or erratic idle and sometimes sluggish acceleration.

I have a quick cure for this problem. In fact, this cure will work for any car that has a throttle body.

The issue is that over time a sludgy gunk will build up in the throttle body where the throttle butterfly opens and closes. This gunk will eventually change the airflow characteristics of the gap between the butterfly and the throttlebody which will cause the erratic idle. In addition, this gunk can cause the butterfly the stick as it opens which will effect acceleration.

The car's DME will compensate for this buildup over time, but if it gets too thick, then the "Throttle Adaption" will reach its limit, and will throw a code. Many times people think that it is the MAF that is bad, when it is just a dirty throttle body.



Notice that the butterfly valve is slightly cracked open. This is for the idle airflow, and that crack can get clogged because of the gunk buildup.

The solution is to remove the air cleaner box for access to the throttle body, and simply clean the throttle body with spray carburetor cleaner.

Open the butterfly valve with your hand, and wipe out all of the gunk on the backside of the valve, and the inside of the throttle body. You will see a dark brown ring inside the throttle body. This is the buildup you want to remove.

Take a rag, wet it with carburetor cleaner, and wipe out the gunk. Be sure to get the edge and the back side of the butterfly valve as well. You will know when you are done because the surfaces that you are cleaning are polished, and easy to see if there is stuff left on them.

Here is a picture of what your throttle body should look like after it is cleaned. Notice how the inside shines.



Don't worry if you spray too much in the engine, when you fire the engine up, all of that stuff will burn off in the combustion chamber.

Where does the gunk come from? It is residue from the crankcase vent opening that is right there behind the butterfly. The reason it is there is because there is high vacuum there that will suck the crankcase oil vapors back into the combustion process of the car. Over time oil solids will accumulate there and will form a sticky lip around the opening.

This cleaning should be part of your 30,000 mile maintenance as a minimum. However if you have never had your throttle body cleaned, try doing this weekend. You will be amazed at how much better your car runs.

 

Yes, and furthermore...

 

Very nice additional write-up from over on EuroAuto Forums. That one has all of the disassembly pictures on it that all Rennlisters know by heart!

 

OE...you must drive your car indoors...that thing is so clean...I've never seen a new one look that good.

 

Thanks for the compliment but actually:

I just finished a 5200 mile road trip with the car. California to Dayton Ohio and back in 8 days. And unfortunately, I drove for 60 miles through the wildest thunderstorm I have been in for a while. Here I am about to go into the belly of the storm on I70 east 80 miles east of Denver. The car is now like a dirty dog, and will need a through going over tomorrow as this is Pebble Beach weekend.



The car rolled over 60K miles on the trip, so I did the 60K maintenance on it today. That is how I discovered how bad the throttle body was, and decided to clean it.

But despite this dirty throttle body, the car returned an average MPG of 29.4 for the trip at an average speed of 70 mph. (I think it was more like the mean!). Absolutely no problems were encountered on the trip.

 

Both great writeups with easy to follow steps and pictures. My compliments to both "chefs". I'll be doing that DIY this weekend.

 

Never worked for my car. Tried twice and my passenger seat still vibrates a little.

 

By fluke I did a modified orang cap mod last night and while the air box was off I wiped the TB clean. On reassembly I felt the car ran smoother - chalked it up to the orange cap mod (although I knew this could not be true) but now I realize I probably just did the service you specified. huh!

 

OE...great shot...I have seen those clouds before

 

I followed everything until the process with the "key and the ignition at the end"....do I have to do this with a 2002 Cab...to reconfigure the throttle body settings?

 

Orient that shot is brilliant. Good Work.....

 

hmm... I remember reading somewhere that there is a coating on the inside of the TB or intake ? that carb cleaner will remove and cause other types of problems.....

 

The throttle will readapt itself to the clean throttle body automatically. You should not have to do anything.

 

how ironic! just discussed last week.. https://rennlist.com/forums/996-forum/370242-weak-sounding-intial-engine-start-up.html

 

Brilliant minds think alike!