Hey guys, what's up.

I have a 1995 Deville that I got 3 years ago when I was 18. It was VERY cheap because of it's mechanical condition (but looked like brand new). Now in great shape, just passed 150,000 miles.

Recently, I have aquired a cold idle problem. The cars idle is unstable. It doesn't miss, it's just unstable and fluctuates +/- 100 rpm from about 550 to 700 rpm. It does this a lot cold and perhaps when it's warm as well, but just not as noticeable when warm.

When I got the car, it hardly ran. So, I tore it down. My first big car project. I replced the following:

All top-end gaskets (Intake Manifold, Valve Covers, Throttle Body, Egr...and such), but no headgaskets
Valve seals
Cap, rotor, wires, plugs.
All 8 fuel injectors (I found that 2 of these, and a loose dist. rotor were the reason it hardly ran when I got it)
Fuel, air, and transmission filters
PCV valve
Belt

and I think that's about it.

Trying to track down this problem, I found faulty and replaced the fuel pressure regulator.

Other things recently replaced:

ignition control module (dist. signal interrupt code...this fixed it)
both oxygen sensors
egr valve and controller (perhaps not needed)
all rubber vacuum connectors
complete exhaust system

All parts on this car are genuine AC Delco, including the plug wires. The only exception is the Walker exhaust system and Bosch plugs and O2 sensors. I have a hook-up that gets me 50% off of list price on all GM parts :)

I also cleaned the air temp sensor on the intake manifold

Going into the diagnostics, I checked the tps reading. It was 0.5 when warm and did not fluctuate.

Yes, the throttle body and egr tubes are clean. They are still very clean from the big job 3 years ago

I am at a loss as to what could be causing this, but it's annoying. One thing I have noticed is a howling noise with the engine running coming from near the p/s pump, which I also replaced last year(the reason I replaced vacuum connectors). The strange thing is, this noise goes away when the a/c compressor kicks in....

Any ideas??? I've been very good to this car because of the price I got it for. As you can see, I wanted a good start when I got it, and i did get a good start. I want to keep it nice... I'm very proud of it. There is a picture of the engine bay attatched form after I finished the big teardown :) Not the slightest hint of oil on that motor. Just nice silver aluminum block :) had about 120,000 on it at this time.

You might have a dead cylinder or a valvetrain issue. You might want to check the compression. Here's an easy way to check your engine compression without doing too much.

Remove the fuel pump fuse. Start the car and let it die. Then, crank the starter for about 3-4 seconds and listen to the way it sounds. Generally you should hear the starter slow down each time it turns the crankshaft and a piston compresses the fuel/air charge. If you hear a skip, where the starter appears to have no trouble compressing the charge on a cylinder, chances are you've got a dead cylinder.

Perhaps a bad ISC motor? Or distributor shaft wobble? Just some other ideas.

Perhaps it's the bosch plugs, some folks have reported that some kinds of bosch plugs don't work so well in the 4.9.

haahahaha, funny you say that....I thought to check the plugs. But I figure while I am pulling them out, I'll replace them again anyway. But I bought Bosch again. There was Platinum +4's in there, I replaced them with plain Platinums.

But I only did the front side that day since i didn't have the time to start the back ones. I might finish today.

The old plugs looked fine, all burned evenly with no signs of contamination or damage.

I'll see if there are any changes once they are all replaced

I don't have a multimeter or the specs to check the ISC. However, it seems to move as it should. It extends when the a/c compressor is engaged and retracts when it is disengaged. It does not move otherwise, even during the erratic idle

I don't have a multimeter or the specs to check the ISC. However, it seems to move as it should. It extends when the a/c compressor is engaged and retracts when it is disengaged. It does not move otherwise, even during the erratic idle
Run cylinder ballance test. Definitely sounds like ignition problem.