Engine...

I have a 2004 Cayenne S 4.5L V8 with 107,000 miles. Every time I come to a stop in either 2nd or 1st gear, the rpm's drop below the normal idle then returns back to the normal idle rpm.
It has been doing this for the past 10,000miles.

I have used a few fuel cleaners through out its life. Lucas and seafoam. So the fuel system is clean.

Thanks for the help!

 

And in your other post you mentioned the cruise control isn't working right?

Have you checked the throttle body? It may need cleaning. When electronic throttle bodies get gunked up (tech term) they often get sticky and won't respond to small inputs - which is what the idle requires.

As far as fuel cleaners - the only thing I'd use is Techron. IMHO Lucas and Seafoam are snake oil (anything that claims to do so many things so well usually does nothing well at all..) And adding fuel cleaner to the fuel system (gas tank) won't do a thing for anything upsteam of the injectors and intake valves.. like the throttle body.

You can likely find an R&R for the throttle body if you look for the coolant pipe replacement DIY's here or on Renntech. If it was me (and I have done it) I'd remove it from the throttle body and very carefully and slowly open it, and clean both sides of the plate and the bore of the TB. Use carb cleaner. Clean until a clean rag comes out without any discoloration. While it's off check the plastic pipe that mounts to the bottom of the Y that leads into it. You may also want to order the TB to intake gasket and replace that while you're there. It's a rubber gasket and by this time it may have hardened up and not be sealing so well.

Don't spray down the intake pipes (toward the air-cleaners) since that will contaminate the MAFS.

If that doesn't work - go buy some CRC MAF cleaner, and clean the MAFS. DO NOT touch the surface of the MAF sensors with anything but the spray from the cleaner.

Checking all the vacuum lines under the hood is also a good idea at this mileage.

If your TB has never been cleaned in 107k miles I can guarantee you it needs it. Mine needed it at 55k miles and you're close to 2x that.

 

I will work on the throttle body. I changed the air filters about 5,000miles ago and cleaned the maf's with CRC MAF cleaner.

Yes, the cruise is also not working.

Seafoam works well. I have even used it to clean the piston in my snow blower. It lifted the buildup and discoloration like it was nothing.

 

Was that by dribbling it in the intake when the snow blower was running? Water would have worked equally as well..

 

No I put the seafoam in through the spark plug hole. Let it sit for a day. All of the carbon was lifted and it simply wiped right off.

 

I cleaned the throttle body very well with CRC throttle body cleaner I got from autozone. Then I carefully removed the plastic cover to the gears on the throttle body, I lubed those. I also lubed the throttle valve. I also cleaned off the MAF's with CRC MAF sensor cleaner. All of this did help the engine's operation, but I still have the drop in rpms when I come to a stop. They are not as prominent, but the issue is still there.

The throttle body was very dirty, I am glad that I cleaned and lubed it

 

Since you're on the throttle body kick, you should do a TB adaption too. 1.After the engine has been shut off for at least a minute turn the key to "on" not start. 2.Leave ignition on for at least a minute. After about 30-45 seconds the TB motors will cycle. Listen in the engine compartment for buzzing/clicking. 3.Turn the key off again and wait another minute. I don't know if this will help your idle issue, but its another "can't hurt".

 

Thanks! I will do that.

I have actually had that situation happen and thought those noises were so weird!

But I will purposfully do that key on TB cycle soon, and let you guys know.

 

I removed the negative terminal wire under the little plastic cover at the drivers seat to reset the computer. I also had the lights on to help drain the system.
I let it sit for about 15 min. It did not "FIX" the low rpm issue when the car comes to a stop but the accumulation of efforts has had a huge effect on getting most of the issue to go away.

The low rpm issue is almost not even there. Not sure what to do from here but keep it maintained

 

Disconnecting the negative terminal on the floor of the drivers seat and letting the car sit for about 20 minutes did not change the idle issue. I am sure it helped reset other things but it did not improve the idle issue.

The biggest change was cleaning and greasing the throttle body.

I will try seafoam again when I get to 6,000 miles on this oil. I will put one can in and drive it for about 100 miles then change the oil. I will still use lucas and seafoam as fuel cleaners here and there.

I will just keep it well maintained until I can find another way to fix the idle issue, even though it is not hat bad.

 

Is it throwing any codes? Could it be coils?

 

I dont know. There is no CEL light. Yes they have been replaced.

 

The 2 top vacuum lines were cracked. Replacing those helped but did not fix the issue 100%. It is not bad but it is annoying.

 

Did you ever end up figuring out the rough idle situation ?

 

It is still there.
After cleaning and lubing the TB, Replacing both air filters, cleaning the MAF sensor, replacing the 2 top crank case vent tubes, changing the oil, fuel cleaners, there is still a low idle rumble when I come to a stop.
Then the idle returns to its normal RPM.
Although, from all of this it has improved.

All of the things I did to the car I am happy with and glad I did them.
They are all good for the care of the car and are necessary to keep it in good working condition.
But I dont have any new ideas to fix the issue.