2004 Cadillac Deville idle

I would probably monitor the fuel pressure at the moment this is occurring. Indications are that the system is going lean for some reason and losing fuel pressure would be a likely cause.

I will hook up a gauge to that today I didn't even think of that. What should it be? About 40-50 right? Also I'm trying to bench test the TPS, MAP, MAF, AND IAC can someone give me these specs and how to test them? Maybe a direction of a website on these specs and instruction. Also could the EGR or EVAP be doing this? I'm beginning to think it's the ECM and I'm not happy.

The fuel pressure spec for that engine is 41 - 47 PSI.

As far as other diagnostic info you can get a single vehicle subscription to www.AlldataDIY.com for a very reasonable price. That is the same data service we use in the professional version.

You also want to clear all those codes to see which ones come back. You may have unplugged something and turned the key on and that would have set some of those codes.

I tested the fuel pressure and it was very erratic and leveled out at about 38psi running. When I shut the car off it went up to 40 and stayed there till I released it. Once I released it for some reason it continually had a little pressure even with the car off. Could a vacuum leak send all these sensors into a fault and make the engine race like this. The car won't idle normal it is always idling at like 2000 rpms.

I tested the fuel pressure and it was very erratic and leveled out at about 38psi running. When I shut the car off it went up to 40 and stayed there till I released it. Once I released it for some reason it continually had a little pressure even with the car off. Could a vacuum leak send all these sensors into a fault and make the engine race like this. The car won't idle normal it is always idling at like 2000 rpms. The most recent codes were p02l121, p0171, and p0174. How would I clear the computer (I do have a pocket scan tool) and if I cleared the computer by pulling the fuse for 5 minutes do I have to reprogram it or something?

Why are you still talking about sensors? You just proved the fuel pressure is too low.

Last night we decided to take a gamble and we pulled the intake manifold. Thank god we did there was a hole in the throttle body to intake coupling and we also found an injector that the pintle cap was broken on. We had to use a vacuum with a small hose on it to get the pintle cap out of the engine and we replaced everything. The car is now running 100% better. Thank you for your help and if y'all ever hear of a cadillac 4.6 Northstar racing up to like 2000 rpm have the owner or Mechanic look at the throttle body to intake manifold coupling. you can mark this one as solved.

Oh and the fuel pressure is back to normal.

I suspect the fuel pressure problem was more of a faulty gauge than an actual problem. What you found didn't have any effect on fuel pressure. Glad you found the problem though.

I tested the fuel pressure this morning and it was right around 40psi.