[Daddy's Big Caddy]

Hi guys,
I'd need a bit of help here please. 2004 Seville STS 4.6L Northstar. Presently we are in the middle of winter and the car is parked outside, so the car starts its day off 'cold'. After the car has been running for a good while, and she warms up good, all of a sudden it will accelerate on its own. But sometimes it does it, sometimes it doesn't.
Here's what I noticed yesterday:
At idle, it will almost mimic what I do with the accelerator...If I rev to 1500rpm, it will stick at about 1200-1300 rpm. If I rev to 3000rpm, it'll stick around 2700rpm. And so on.
When driving in town, it'll idle and drive around town, I could easily get home without stepping on the gas pedal.
Also, when it does this, it seems to smell of burned rubber.
I removed and cleaned the IAC valve. It had some black soot but it wasn't a disaster either. However, it didn't solve the issue.
No visible check engine codes on the dash. Apart from the issue I mentioned, there is nothing out of sorts with it. (When its not doing the auto-acceleration thing) It will idle normally, rev up and down smoothly, no hesitation or stuttering, no burning or smoking.
Thanks for any help that you can offer.

 

[maeng9981]

When you cleaned the IAC did you also clean the throttle body? Also, check and see if throttle/cruise control cables are binding.

 

[Daddy's Big Caddy]

No, just the IAC valve. I removed it, cleaned it, replaced it.

 

[Submariner409]

Yep - TB cleaning (many threads on this), cable operation check, TPS checks. Carpet or mat interfering with the accelerator pedal?

Make sure the IAC top hat and plunger are screwed all the way into the IAC body.

https://www.cadillacforums.com/forums/cadillac-seville-cadillac-eldorado-forum/205754-acronyms.html

 

[Ranger]

The IAC valve is RARELY the problem. One more vote for a good TB cleaning and I'd be willing to bet you problem will be solved. Be sure to clean the throttle plate AND it's perimeter along with the TB bore.

 

[Daddy's Big Caddy]

Hi guys,
just a quick follow up. Yesterday, I bought a new TPS (mine was original and 15 years old) and can of throttle cleaner. Removed the throttle, cleaned in. It was dirty, very baked on, hard, black soot. Got her all nice and purdy. Swapped in the new TPS. Put it all back together. Starts, idles and runs fine but I'll test it for a few days and see what I get before I consider it 'fixed'. Thanks for your help.

 

[Dlagwa]

Just touching base on your idle prob. Mine did the same symptoms as what you described. It turned out to be the inner throttle body boot. There are two, the one from the air cleaner to throttle body, then a very short one inside the throttle body intake manifold area. Pain in butt to change. The kits are on eBay really cheap and be sure to follow the torque recommendations. The intake is plastic.
You will notice the crappy small design for the throttle body plate. Seems way small compared to the size diameter of the throttle body and intake manifold opening.
Side note, that inner boot is NOT cleaner/solvent friendly. It will deteriorate quickly if exposed to certain chemicals used with throttle body cleaning. Nice engineering job security!!

 

[Submariner409]

Dlagwa, Welcome Aboard !!! Please update your profile. Look at other member login banners for guidance. Thanks.

You're looking at the 2000 - 2005 intake manifold "plenum". Common failure part. RockAuto, $20 with 8 seals.

That failure sets P 0171/P 0174 codes and MAY cause a fast idle problem.

Another common vacuum failure is the PCV dirty air line and connector elbows. Same codes set.

Click to enlarge, follow the lower edge prompts.

 

[Daddy's Big Caddy]

Hey Guys,
it has been a few weeks since I cleaned the throttle body and swapped in the new Throttle Position Sensor. The issue has been solved and is back to normal driving. I wanted to give it a good test period before starting the 'problem solved' celebration.
For anyone having this issue, I'd say that cleaning and swapping in a new TPS is the easy and cheap starting point. Be sure to check all of your air intake boots for cracks that will produce leaks.
Thanks for your help Guys.

 

[pearcetopher]

mine did this too, excessive dirt and gun accumulation around throttle plate would not allow throttle to close all the way but did not set a code.