1999 STS dies at intersections

[Ranger]

A stuck open EGR would cause it to die at idle, but should also set a DTC pointing to the problem. I'm leaning more toward the carboned up TB and blocked IAC passage.

[RunningOnEMT]

if the IAC is blocked then the car is basically relying on the throttle body to keep it running at idle... or am i wrong?

what yis the response time on the throttle body, also if its that caroned up you might not beable to return the plate the proper idle poition regardless of the condition of the motor

[lbwd]

Any luck yet?
This problem sounds familiar because mine did the same thing when I got it. It also would die occasionally in reverse.

My problem was an Ignition Coil.

[noobie]

Yup, I got it fixed. After cleaning the dirty throttle body, the car died less but still die. I also notice that my car shake a bit at idle, so I decided to check the spark plug wires. I couldn't get any measurement for any wires except number 7 wire. So I bought a new set from Advance Auto Parts, Xact is the brand, and my car hasn't die since and it fixed the shaky idle.

I also noticed that inside my intake manifold has wet oil thick carbon build up. Does everyone have the same condition?

Thanks for all the suggestions.

[submariner409]

If the TB was/is messy and the intake manifold is a mess, pick up a handful of gaskets, a new rubber plenum connector, injector O-rings, throttlebody cleaner, some rubber fuel line hose to make new pipe connectors if needed, pipe cleaners (craft shop), fender protectors, and put the car OOC for a Saturday. Make sure you blow/pipe cleaner out all the little vacuum and signal holes in the TB. Be very careful not to drop anything in an open port.......

[Ranger]

Originally Posted by noobie

Yup, I got it fixed. After cleaning the dirty throttle body, the car died less but still die. I also notice that my car shake a bit at idle, so I decided to check the spark plug wires. I couldn't get any measurement for any wires except number 7 wire. So I bought a new set from Advance Auto Parts, Xact is the brand, and my car hasn't die since and it fixed the shaky idle.

I also noticed that inside my intake manifold has wet oil thick carbon build up. Does everyone have the same condition?

Thanks for all the suggestions.

Yes. It is normal. It is a combination of exhaust and crankcase gases that are trapped in the manifold when the engine is shut down and then settle out.

[kjhansen]

Getting back to the basics is always good! The carbon build-up in the intake manifold would SEEM to indicate a lot of oily blow-by (bad rings?) getting into the EGR system and thus back into the engine. Which is what the EGR system is supposed to do (recirculate exhaust gases, thus the name Exhaust Gas Recirculation valve) but I don't think it should be oily and thick... Probably should do a leak-down compression check and check your EGR valve. In any case, getting back to the basics isn't always enough with modern cars. Quite often you need to put the car on a scan tool and see what's happening. Which brings up a question: Who makes a good scan tool for the 1995 SLS? Most of the scan tools I see at parts dealers are for 1996 and later--not to mention that they're just code readers with no record or playback features.
Keith

[Ranger]

The oily part comes from the PCV valve (oily crankcase gases). It is perfectly normal and can be seen on any engine with a dry manifold.

[Vinnyguti988]

Originally Posted by kjhansen

Getting back to the basics is always good! The carbon build-up in the intake manifold would SEEM to indicate a lot of oily blow-by (bad rings?) getting into the EGR system and thus back into the engine. Which is what the EGR system is supposed to do (recirculate exhaust gases, thus the name Exhaust Gas Recirculation valve) but I don't think it should be oily and thick... Probably should do a leak-down compression check and check your EGR valve. In any case, getting back to the basics isn't always enough with modern cars. Quite often you need to put the car on a scan tool and see what's happening. Which brings up a question: Who makes a good scan tool for the 1995 SLS? Most of the scan tools I see at parts dealers are for 1996 and later--not to mention that they're just code readers with no record or playback features.
Keith

I haven't heard of a scan tool for Cadillac, but since having a Pontiac and another Cadillac at home i decide to buy one that did 95 and up. it worked on my parents Pontiac but not on my 95 Cadillac STS or my parents 93 Deville, since they already have a code reader built in the Climate Control Center... so my advice dont buy the code reader unless you want to read off codes from other cars that dont have Climate Control Centers..

[kjhansen]

Nah, I don't want a code reader. The internal one is great on the Seville. What I want is a scan tool. I think the Seville has a kinda-sorta one with the snapshot function. I'd like to know things like throttle position sensor data, idle air control information, block learn mode, degrees of knock retard, O2 milivolts, rich/lean condition, mass air flow, etc.--i.e., the data the car's powertrain control module sees. An ongoing data stream that you could record and then print on your home computer. I had one for my Turbo Regal (about $150 for the program and cable, but you had to provide a laptop) and you couldn't really tune without it. But it won't work on the Cadillac, so I was hoping someone would know about one.
Keith