1999 STS High Idle

The car starts fine, then after a short period of time the idle starts creep up to +3000 rpm. The car has been towed to a Cadillac Dealership, and they can not find any codes. They have had the car for 2 days still no clue. I drove the car from Atlantic city to Philadelphia area just using the brake. The Dealership can't replicate the problem. The tow truck operator report the problem also.I don't trust the car until, they find something wrong. The car has 71,000 mile and well maintained. Please help.

Ask your dealer about a idle senser control....Guys, these 99 sts's have them, right?

Seems obvious imo, the IAC as rickyd suggests.

Thanks, for the responses from Rickyd and Katzmans Caddy. The dealer called us Friday, and told us to pick up the car, they cannot find the problem. The dealer drove the car about 50 miles without the problem. We drove the car home and put it in the garage.
I asked the service manager about the IAC, and he said it checked out fine. Imo the dealer did not want to spend the time ($) to look for something that if not found, they would have a hard time billing. If it doesn't show up on a code in the computer its difficult for the mechanics to diagnose.
The car is in the garage till we decide on a replacement. Lucky for us it is not are only means of transportation.

I think that replacing a 71,000 mile Cadillac just because it has a fast idle is a knee jerk reaction. I think that you can start by replacing the IAC, about $20, and cleaning the throttle body,. MAF and IAC bore. I'd also look at the throttle cables and linkage and lubricate and check for any binding. Check all connections for sensors around the Throttle body  and air box too.

tigerdan.... gee i don't think a caddy service store would pass up a fine opportunity to milk you on this one..... it sounds so simple...... however, if the car didn't act up for him, then he doesn't know what to r/r...... imo he did you a great justice in "not just changing parts"  hit and miss.... Thank that s.a. and return to him when it reaccures...... hows your floor mats?
rickyd

The floor mats are clean and on the floor where they should be. The Service Manager did not charge for any diagnostic time, which was good for me, but raises a question if a technician actually performed any checks. GM dealer mechanic's are paid flat rate if they spend any time on a customers car, the customer gets billed.
I spoke to an independent shop owner regarding the problem, he thought it might be a leak in the manifold gasket or intake. If it had an intermittent air leak would that show up as a code?

hey tigerdan... is the car still acting up?........ as far as your indepentent guy, i do believe you would hear the leak, if there is one....do you? that is a little behond me, so wait for one of the Tech to respond to that one..... as far as a code showing up..... imo, if a check engine light, or dic quote comes on then you'll most likly have a code to follow.   the floor mats were a joke..sometimes they'll hang up your peddle....you got to know my humor....sorry.........good luck dude
rickyd

quote:

ORIGINAL: tigerdan

The floor mats are clean and on the floor where they should be. The Service Manager did not charge for any diagnostic time, which was good for me, but raises a question if a technician actually performed any checks. GM dealer mechanic's are paid flat rate if they spend any time on a customers car, the customer gets billed.
I spoke to an independent shop owner regarding the problem, he thought it might be a leak in the manifold gasket or intake. If it had an intermittent air leak would that show up as a code?

hows it goin?????   new caddy, or did you fix the one you have????
rickyd

had the same problem change the plintum gaskets also called the intake gaskets there are 8 of them did that on my 02 sts did not know they were leaking till the starter went out.