The first time it happens was last month. in the early morning, I start up the car to drive to work (outside temp around 66degree). The car rev up and down. Up to around 2k+ RPM and down to around 500RPM. I checked around the engine, but nothing look strange....so i drive it to work. it drive fine/idle fine after driving for about 2 minutes. this problem happens for couple days in a row...then it fine after that.

A month later, it happens again (same as above).
I stopped by the grocery store and come back out in about 5 minutes, then start up the car, it rev up and down again.

--> that mean the car rev up and down in both COLD and HOT engine.

There is NOTany "Check Engine" lights on. The thing is it runs fine after driving for 2 minutes. sometimes it does that, sometimes it doesn't.

What could be the problem guys?
(99TL 116kmiles)
thanks.

 

try checking the IAC Valve, same symptoms that I had. I replaced my IACV and the possessed engine revs were gone.

 

Check you coolant, thats a sign of not enoght water or a bubble in the line, also IACV as well.

 

Every now and then I get the same revving action but only when in D and pullin outta the house in the mornins. It will idle fine in P but when I stop at a crossroads when I leave in the morn I can feel the rev jump up slightly then back down...they're not nearly as bad as Midwest's...only about 100rpm...but enough that the car will move forward a bit if I'm not on the brakes hard enough.

Didn't mean to steal away from Midwest. Sry bro! Gonna keep an eye on this thread...

 

When I had this problem I remove my throttle body. Next I clean an spray out my Throttle body with CRC air-intake cleaner, b/c the vent got stuck. This solve my rev up an down problem.

Good Luck Midwest

 

thats another way of saying the IAC (Idle Air Control Valve) needs cleaning

remove the Throttle body Assembly- taking care not to tear the gasket attaching it at the manifold
Turn unit over and remove the 2 screws on the small cover plate- remove the piece inside there and clean everything with carb cleaner spray- put it back together

Make sure to clean the 3 inch round plate inside the TB- use the outside spring mechanism to move the plate to the open position and clean the edges and back- use a toothbrush if its really bad but get it clean!!

be careful not to make the bolts too tight on the TB, before you remove them- pull on the wrench gently - see how tight it feels to your muscle, so when you put it back on you can tell when its back the same tight
If the gasket is torn or damaged get one from the dealer
Hook any vac hoses and coolant lines back up and start the car

 

Finally had a chance to clean it on Sunday. After cleaning, it runs great. no hick up so far. Thanks all.

 

there ya go bro

 

what did you clean and how--so the next person knows

 

That explains it there.

 

I love being right-
please tell my wife I was!!!

but what did the OP do?

 

LOL.
If I did, she probably Wouldnt beleive me!

I'm sure you know how tht goes. Your alwys wron, unlike her.

But anyways. My car did this before the day after I bought it. Never had the problem again. Pretty weird.

 

I didn't take the pictures, so hopefully with my general description below can help someone taking it out easier. English is my second language, so bear with me.

To get to the throttle body, we must start out from the air filter side. The tube from the air filter to the throttle body has 2 parts.
==First, take out the air filter and the first part out. The first part is the part that cover the air filter. unplug all the hoses that attached to it.
==Second, take out the second part. unplug all the hoses that attached to it.
==Third, unplug the electrical and hoses that attached to the throttle body. I DID NOT take out the spring mechanical that use to control the plate. I was thinking if I messed that up, my idle speed will not at correct position.
==Forth, unscrew all 4 screws and take out the throttle body. careful with the gasket. if damage replace it.
==Fifth, take it out. The 2 wires that comes from the gas paddle still attached to the throttle body, keep it that way. That mean you can't take it completely out of the engine, so what I did was get a pan (oil pan) and put the pan in the spot of the air filter and put that throttle body in it, then I pour in little gasoline, then use the brush to brush it off.
For the inside, I use a little clean cloth to rub it. I also use the the finger to push the plate to have it turned side way so that I can clean all around it.
Finally, use clean gasoline to give it a final bath. then set for few minutes to have all gasoline there dried out.

Now put them all back in the reverse order of what you take it out. Pretty easy and it takes average handy man like me 15 mins to find the tool and take it out, 5 mins to wait for it to dry and about 10 mins to put it back. Roughly about 30mins total.

Maybe it is a little easier for me because I cleaned the EGR port before. yeah, I did clean the EGR port without cleaning the throttle body.