: Idling Trouble for 2004 Deville

12-10-12, 02:58 PM
After an abrupt incident when my car would barely run, I replaced the Idle Air Control (IAC) sensor after cleaning the Throttle Body (TB) and the old IAC did not help much. After training the new IAC with information found here, the car will run somewhat consistently with the exception of idling in parked or while stopped. I get PCM P0499 trouble codes consistently and had previous fuel efficiency issues and also have problems with the fuel gauge providing stable data. The car has 118000 miles and also seems to accelerate itself at times. It also seems to keep the brakes from working especially after starting and driving until it warms up?

12-10-12, 04:56 PM
PO449: Evaporative Emission (EVAP) Vent Solenoid Control Circuitcode

12-11-12, 10:50 AM
Thanks for your reply very much. Any direstions on the solution would be appreciated also!! Also get PCM P0300 at times also. Very sputtering this morning with a wetter colder night last night. Also got some RPM jumps after idling with the foot on the pedal to keep from stalling this morning and once moving, it appears to not shift gears as smoothly as before.

12-11-12, 03:55 PM
This belongs in Engines: Northstar Performance: P codes, in and of themselves, do not normally point to PCM troubles.

The "PCM tuning" Forum is for the modification of GM PCM's other than the 1998 - early 2004 Northstar FWD series.

A DTC of P 0300 (C or H) shows a "miss detected". When was the last set of plugs installed, and what make/model were they ? Air filter, intake ducting checks, vacuum hose checks, throttlebody cleaning, Idle Air Control (IAC) cleaning, injector checks, intake manifold plenum connector check - many possibilities for a miss.

ALL of that can be found by Googling "cadillac forums 2004 northstar throttlebody cleaning" or other system/part. You might want to surf through the pages of threads in Discussions, Item Specific: Cadillac Tech Tips. Go through the pages of threads in Engines: Northstar Performance until your mind warps.

12-12-12, 01:46 PM

01-03-13, 10:09 AM
Just as an introduction, I had this proble that I was seeking expert assistance for:
2004 Deville:
My car would not start, and I left it alone for two hours and then it started but idled at 1500 RPMs. I then checked the codes and had 300, P0106, P0107, P0171, and P0174.
I found that the IAC valve was broken (three pieces), so I replaced the IAC and cleaned as far as I could reach in the throttle body (I did not remove the throttle body). The car then started but, when in cruise control ,at say 35 MPH, the RPMs jump between 700 and 1600 (it does the same if I take my foot off the gas, it can speed up then slow down and then back up. This condition gives me codes P0106, P0171, and P0174. I have also changed the MAF and MAP with no improvement or change in codes.

The above is very close to the problems that your are experiencing.

My expert suggested that I use starter spray and spray it around the vacuum hoses and throttle body. He stated that I will see an increase in RPMs if i spray an area that has a leak
When I tried this solution I found two leaks. One was on a rubber elbow that comes off the top of the throttle body, and the second was around the throttle shaft (this is where the accelerator cable connects to the throttle body.
The first piece is difficult to find, as my dealer wants me to purchase a set of all vacuum lines (way to expensive), and i am still looking. For the second problem, I will most likely have to buy a new throttle body as the are no rebuild kits available for the threottle body my deville has.

I suggest you try the starter spray solution as it is not expensive and could point you in the right direction.

Good luck, and let me know if it helps.

01-05-13, 04:15 AM

The elbow piece can be found in the "Help" section of a well stocked store.

Look where the vaccuun lines or pcv valves are kept.

Bring your disintergrating elbow with you to match up the fitting ends. If it's a little smaller at the fitting ends, that's ok.

Bigger is not going to be good.