Plz Help, Code P0506, Tried EVERYTHING!

C-NOTES · #1 (**permalink**) 08-10-09, 02:29 PM

Hi, I have a 2002 Cadi Seville STS (95k). I started having this problem several months ago and I've worked with a mechanic trying to chase this problem down. When I'm driving, the car accelerates by itself and I have to ride the brakes at times to stay within the speed limit. At stoplights, the car wants to move forward and if I put it in park or neutral, the car idles at 1000+ rpms, sometimes greater than 3000 rpms! If I tap the gas, the engine revs and continues to rev for 30-60 seconds before it starts to come back down.

I took it to a friend who checked for all vacuum leaks and none were found. It needed a tune up so we replaced the spark plugs (AC Delco), air filter, fuel filter, etc. and when we were looking at the problem, he ended up replacing the TPS and cleaning the throttle body. It drove OK for a while but then it started acting up again.

Recently I got a message asking me to check my gas cap. After a week of that, I cleared the codes and that message has not been back since. I took it back to my friend who checked for vacuum leaks again and replaced one of the connectors that was dried out and brittle then gave it a really good throttle body cleaning. Now when I start the car, the idle is usually low (around 500) and sometimes dies on startup unless I give a little gas. A week has gone by since he's done the cleaning and the high RPM problem is starting to come back slowly. I'm out of suggestions and was hoping someone here could help me out.

The only engine code I'm getting is P0506 and it's for a low idle which doesn't really tell us anything that we don't already know. Any and all help would be greatly appreciated.

osu411yamaha · #2 (**permalink**) 08-10-09, 02:38 PM

TPS. Throttle Position Sensor. They only cost about $30 bucks and are easy to change. Get a can of throttle body cleaner and clean your throttle body while you are in there.

submariner409 · #3 (**permalink**) 08-10-09, 02:40 PM

ISC/IAC (Idle Speed Control/Idle Air Control) system ??

C-NOTES · #4 (**permalink**) 08-10-09, 02:54 PM

Parts I replaced:

TPS
Cam position censor

No vacuum leaks, throttle body and ISC has been cleaned VERY thoroughly.

I suppose the next step is to replace the ISC. I have also heard stories about a leak in the intake manifold may be the culprit. Is that worth exploring?

**Ranger** · #5 (**permalink**) 08-10-09, 05:56 PM

Before you replace any parts check for a vacuum leak at the manifold over pressurization valve behind the P/S pump as well as a leak at the plenum. That is a common problem on the 2000+ engines. Either one could cause your problem. Also don't overlook binding linkage or a floor mat interfering with the gas pedal.

submariner409 · #6 (**permalink**) 08-10-09, 06:00 PM

The leak you refer to, in the manifold-to-throttlebody connector plenum, usually sets O2 sensor lean codes and contributes to a choppy, rough idle, not excessive rpm.

Get a stethoscope from Walgreen and replace the chest diaphragm with a length of vacuum hose from any parts store blister pack rack. Use the rig to track down vacuum leaks and strange ticking noises.

The manifold and plenum can be tested for vacuum leaks by stareting the engine and judiciously spraying either choke cleaner or starting fluid at the site of a suspected or possible leak: any leak and the idle speed will change noticeably from the added "fuel".

**Ranger** · #7 (**permalink**) 08-10-09, 06:03 PM

True, but I think it is still worth checking first.

reelbros · #8 (**permalink**) 09-27-09, 09:53 PM

C-Note
Any luck finding a solution? My 2000 STS began the EXACT symptoms last week, I ran my dash OBD it showed a p0506 which is IAC? I replaced PCV
and checked for leaks...Scary at stop lights!

Thanks Todd

MCD0MINGUEZ · #9 (**permalink**) 10-05-09, 05:17 PM

My car is experiencing some of the same symptoms (P0506 P0507) the local cadillac dealership told me to replace my whole throttle body assembly including the Idle air control, throttle position sensor, and throttle plate. They want around $350 for the parts.

submariner409 · #10 (**permalink**) 10-05-09, 06:28 PM

Bat crap !! There are a skrillion threads, with pictures, on how to clean the TB and IAC - one within the past 4 days with a slew of pictures. Maybe in Deville or Northstar Performance. Piece of cake.

C-NOTES · #11 (**permalink**) 10-20-09, 12:53 PM

Hello everyone, sorry for the delay but I've been away on business and just resolved this problem last week.

The problem was the IAC valve. @ $360+labor it was a tough pill to swallow but that was the problem. Now the car runs fine and hopefully I'll go for a while without any more problems.

I'll check back a few more times in case any of you have any questions.

C-NOTES · #12 (**permalink**) 10-20-09, 01:06 PM

I don't know where my other reply went but I finally got the problem resolved last week. It turns out the IAC valve had to be replaced at the cost of $360 plus labor. The problem is now gone and the car drives much smoother. I hope this helps and I'll check back periodically to answer any questions.

submariner409 · #13 (**permalink**) 10-20-09, 06:28 PM

www.rockauto.com lists our AC Delco IAC for $206. The labor time is one can of beer, one connector and two screws.

C-NOTES · #14 (**permalink**) 11-07-09, 11:23 AM

Thanks submariner409, unfortunately we weren't sure if the IAC was the problem so my mechanic had a deal with Napa... if that's the problem, we buy the part from them. If not, we can return it without questions. Thank you so much for all your help.

00 Deville · #15 (**permalink**) 11-07-09, 11:31 AM

Quote:

Originally Posted by C-NOTES

Thanks submariner409, unfortunately we weren't sure if the IAC was the problem so my mechanic had a deal with Napa... if that's the problem, we buy the part from them. If not, we can return it without questions. Thank you so much for all your help.

That's a good deal he has with NAPA... most places won't take back electrical parts and the IAC is one damn expensive part.