1999 SC2 wont idle??
 

My 1999 suddenly started to die every time I stop? the engine light is not on and it runs good otherwise. I pulled all of the spark plugs and they were all clean, I cleaned the throttle body and sprayed more while it was running looking for a vacuum leak but no luck there? I thought it might be a bad tensioner pulley so I removed the serpentine belt and started it, still wont idle? any thoughts on what it could be? Thanks for any advice.

Check the ECTS. Engine Coolant Temperature Sensor. This sum beech has been a major headache for many an S series owner. The first thing to check would be the connector. It's a squeeze type, so don't yank on it or twist it trying to get it off. You simply squeeze it on the sides and pull it straight out. If the connector looks okay, odds are the sensor is shot. You'll need to get a new, brass tipped one, from a Saturn friendly GM dealership. You need to get another pigtail too, just to be safe. Total should be about $50. The ECTS is located on the drivers side of the car and screws into the engine head. If you just do a search here, I'm sure you'll find numerous posts about it. And welcome to the forum. I'm also a Mopar man.

Thanks, I have changed that about 1 year ago but it was from auto zone or orielys so I guess it could have gone bad again. when I changed it last time it was because it was overheating. I also ended changing the water pump and thermostat and about 2 weeks later the radiator started to leak so I changed that as well and all was good until about a week ago? what kind of mopars do you have?

When it DID idle properly, at what rpm did it idle?

1999 what? SL1 SC2? Mileage?

Sounds like it won't idle at all, not just when you stop. If you feather the gas pedal can you keep it running?
When you cleaned the throttle body, did you clean the IAC (idle air control) passage at the bottom of the throttle body.?
Clean air filter?

Does it shudder and die or just outright stop?

1999 sc2, 180k miles. I can feather it and keep it running but I usually put it in neutral and still have to step on it a bit to keep it running. it would idle fine before usually at about 800-1000 rpm. cleaned everything out and it actually was not dirty at all. air filter is clean and was replaced about 5 months ago. sometimes it stumbles a bit before it dies but usually it just dies as soon as I let my foot off of the gas. Thanks.

800-1000 is too high for an automatic s car when warmed up. Oh, title says SC2. Oops.

High idle makes me think vac leak. Automatic should be 750 rpm. I know you said you sprayed around for a vac leak. Check again, concentrating on the throttle body gasket and the intake manifold at all four cyls.

Still wondering if there isn't something hanging up the IAC such that it cannot adjust properly near idle. Based on the 800 to 1k, was it consistent at some rpm, then also consistent at another rpm on the next drive?

Just a guess that IAC may have been acting up for a while and now cannot function at idle.

Per Rube, the ECTS is not out of bounds. If the fuel mix was so rich as to stall the engine had a harder time starting right away, i would think you would have had a harder time starting it

I think it was about 750 or so looking at it now. when I first start it, it will usually idle fine, then as it warms up it will no longer idle. I checked again for a vac. leak and sprayed a bunch and no idle change at all. I drive this car every day to work and back 40 miles each way and idle has been perfect, then all of a sudden it started to die?

Strange.

An s series DOHC, ice cold, usually idles at about 1000 to 1200 rpm at cold start. As engine gets to operating temp, the idle slowly drops to about 800-850 for a M/T and to around 750 for an A/T.

So if it is cold, it is not programmed to try to run that low with the initial super rich fuel mixtue called for by you guessed it, the ECTS. The mixture needs to lean out first based on the engine temp increase reflected by the ECTS reading.

But if you are now saying it starts, idles at 750 from the start, then, while warming up .it cuts out and will not idle on its own......

The specifics you're providing regarding the car's behavior keep changing. Please don't rely on memory as to what's going on. Please sit in the driver's seat and write down what happens from s cold start, in what order, and come back and post a definitive set of behaviors we can run with. Right now, some info contradicts previously posted info unless I am misinterpreting stuff.

I'm not trying to be a jerk. I'm trying to help you. And I can only do that from where I sit with a solid description of the problem.

Derf

I went out and started it this morning just with the key, no gas pedal, it would start and die right away. It did that 3 times. I started it again and revved it up a few times and it started to idle smooth at 1100. turned it off and restarted it a few times with just the key and it idled at 1100 each time. drove it around about 20 min and all was good, came to a stop and it died and would no longer idle? I would have to put it in neutral at each light and rev it up a bit to keep it running? Thanks again for any help.

Did the car ever idle on its own after you began driving it? If so, at what RPM?

I'm trying not to over think this, but it almost sounds like your idle air control (IAC) valve is hung up. Like it's trying to adjust for the correct amount of air at idle, but can't move properly nor quickly enough to get to the needed position to keep the engine running at idle. It just so happens it hung up allowing enough air to idle at cold start. As the engine warms up, the air fuel mixtue leans out as the car goes into closed loop control, relying on feedback from the ECTS, O2 sensor, MAP sensor, etc. The PCM continuously futzes with air to fuel ratio as it is programmed to get the engine idling around 750 800. There are codes for "unable to enter closed loop control" and "high idle", but as I typed that I realized your issue is not one of high idle it is one of superlo non-existent Idle so ignore the end of that last statement that I am too lazy to delete.

You did not complain of any driveability problems during your 20 minute drive other then stalling when you come to a stop.

In the back of my mind, there is a chance that your EGR valve is stuck partly open at startup and is not closing all the way when you take your foot off the gas. If you've never cleaned it it is a possibility. Usually you will see issues appear when the car is decelerating right after you take your foot off the gas. Sometimes the RPMs will go crazy other times it will just act weird and then you know you are headed for a stall. The car stalls and you cannot restart it for about 30 seconds, then you restart it like nothing ever happened.

But you have not described any such behavior.

It's cheaper to buy some choke cleaner, pull the EGR, and inspect. It needs a cleaning at your mileage even if it is not the root cause.

Maybe that's all it is. Can't say I've ever come across an s car with an EGR so filthy it could run fine unless the decel pulled the RPMs so low it couldn't move the pintle and stalled every single time.

But there's a first for everything