1997 Cadillac Deville, Erratic / High Idle, Code P0507

This 1997 Cadillac Deville came in with the complaint that the idle speed would sometimes be okay but most of the time as the engine warmed up it would get progressively higher and higher until the engine would run at about 3000 rpms on its own with no throttle input. The following picture shows the engine with the Northstar trim panel already removed.

I located the source of the problem to be a large and varying vacuum leak at the backfire pressure release valve located at the end of the intake housing behind the power steering pump.

Since the cover was already removed I did not have to take that off. I started by removing the intake hose from the throttle body. Disconnected the wiring from the throttle body.

Since I wanted to reseal the whole intake anyway I took the mass air flow sensor, the throttle body and the adapter plate loose from the intake.

There were multiple cables, hoses and tubes that had to be disconnected along the way.

Next I had to disconnect the fuel lines. Because this vehicle had been sitting for several hours I did not have to worry too much about relieving the fuel pressure. You may have to and be sure to follow manufacturers procedures for doing so. I do not want you to set your car or yourself on fire!!!!

This is the tool I used to disconnect the fuel lines.

I disconnected the front spark plug wires and folded them to the rear of the engine compartment. Disconnecting the wiring for the fuel injectors and removing the hold down bolts was next.

With everything removed I lifted the intake off and set it on the floor to start removing the backfire valve. The one thing that I wish I would have done is this. Before lifting the intake use a shop vacuum, air hose or visual inspection to make sure there is nothing sitting on the outer edges that could fall inside the engine. When I removed the intake a spotted a metal bushing that supports the engine cover that had fallen down and was sitting on a ledge about to fall into the engine. I had to spend quite a bit of time examining the lower intake port for other debris that may have fallen deeper into the engine. This would have been catastrophic but luckily nothing else did and all was okay. I did however worry about it right up until the time I restarted the engine.

Anyways, now that the intake was off I set it on the floor with the throttle plate area down on a clean rag. The backfire pressure relief valve was pointing straight up and using a pair of needle nose pliers I removed the valve as shown in the next picture. I am sure some one makes a tool for this but the needle nose pliers is all I had to work with on this one. It also took a lot of torque to remove.

A comparison between the new and the old valve.

The back side of the valve. Notice the alignment / locking tabs.

The corresponding alignment slots in the intake.

Drop in the new backfire valve and twist into place using the tool of choice shown earlier.

I installed a new o-ring gasket for the throttle body adapter plate. The manufacturer recommends to replace this gasket anytime the plate is removed and do not lubricate.

I installed new gaskets although technically they can be reused if no damage is seen but really all of this work and the gaskets are 12 years old with 150,000 miles on them. I don’t think so!

The manifold back in place and almost ready to start. Just a few more things and I will be done.

I ran out of pictures because of an unusual occurrence. While installing the fuel rail hold down bolts with spacer tubes one of the plastic tubes shattered and hit me in the forehead. Although I was not badly hurt it did make me lose my concentration on taking more picture for this post. The thing that surprised me most about it was that I was using a torque wrench set to the proper setting and it still broke. After buying a new spacer and trying again I spotted what had happened. the flat washer on the stud / bolt was bowed into a slight cup shape and this shape was throwing the torque of the bolt off and was applying outward pressure to the spacer instead of just downward pressure this made the spacer split and explode. I found one of the pieces fifty feet away from where I was working. So my advise is to check the flat washers to make sure they are flat before starting and replace any that are not.