Hi everyone,

New to the forum although I've read many posts over the past week. Thanks for the great volume of knowledge that is shared out here.

I've got a 99 SL2 with 252K miles. It recently has been having problems with either a high or low idle depending on engine temp. Usually I just gave it new plugs and cleaned the TBI and that resolved the issue. But not recently.

It threw an EGR code (P1404) a few months back so I cleaned it and everything was fine for a few weeks before the symptoms/code came back. Cleaned it again with the same results. I replaced about a week ago along with the ECTS as recommended in several other posts.

It ran fine for a few days (except for the high idle) but today it's low idling and stalled a few times at intersections while the clutch is in. It did kick out the ERG code (P1404) again but I thought maybe it was relearning after replacing it.

Any thoughts on what to check next?

EGR, ECTS, O2 (upstream), plugs, plug wires are all new within the last 50-1000 miles. I will replace the plugs again soon (to NGK - was unaware of other type plug issues).

 

When you replaced the ECTS, did you also splice in a new connector? They're a known problem too. If so, did you clear the EGR passage as well as the EGR valve. The passage in the intake also clogs with carbon. A good stiff wire and cranking the engine will help blow that crap out.

 

Charlie,

I did not replace the connector as it tested fine via the information I was able to locate on resistance, etc. When I replaced the EGR, I did clean both port hole that lead to the engine. They had considerable carbon build up in them so I got as much as I could and used a small vacuum to remove the debris.

Today during lunch I removed the throttle body and cleaned it. It was VERY dirty. Seems to have helped quite a bit but RPMs still drop to about 500-800 before recovering to a more "normal" 900.

One thing I forgot to mention in my original post was that I also had to replace the starter (when I replaced the EGR). In disconnecting the battery, is there a learning curve for the emissions and fuel systems?

 

I don't know about a learning curve, Gary. Sounds like you've got a vacuum leak somewhere around the throttle body now. Double check your vacuum lines and did you replace the tbi gasket or reuse the old one? If you didn't put a new one on, that MIGHT be the source of the vacuum leak.

 

since disconnecting the battery clears out certain parts of the PCM's memory, a drive cycle (you can search this for saturns on this site and the net) need to be performed before all the sensors are considered "ready". Don't get me wrong, everything is still running closed loop (if the PCM is functioning properly) so you shouldn't get the funky idle behavior you describe.

Don't know about fuel system...wouldn't think there's much to re-learn here -- injector pulse width and fuel trim are calculated and adjusted on the fly.

You've mentioned low idle rpms -- what are the high idle rpms? And which ones occur at what engine temps?

Also, I'm inferring from your post you've had this issue for a while but the old cure no longer is a cure. How many miles has this been going on for (cumulative since it first started happening way back)?

 

Thanks for the info on the drive cycle. I had not seen it previously and know I haven't met those requirements.

The idle issues started about five or six years ago and have happened about the same number of times. I believe it was ~120K miles. When she idles high, it is 2500-3000 then takes a few seconds to return to 900-1000. All idling issues occur when the engine is cold and hot but and possibly more frequent when cold but I haven't really noticed a difference.

I just replaced the plugs with NGK so I'll get the drive cycle down tonight and see how that goes. When I drove it after replacing the plugs it seemed "normal".

I wouldn't worry about it too much if I drove the car but it's going to my 16yo son who doesn't have the experience or coordination to clutch, brake and throttle at the same time....

Thanks for the great input/advice...

 

Just teach him how to throw it into neutral when it does this, Gary. At least until you get it straightened out.

 

Thanks again for all the advice. After a few days, the idle returned to "normal" and she's been running fine since.

One weird quirk that I still haven't figured out..... Three times now, I've gotten a P1404 code which suggests and EGR problem. I replaced it new so I'm wondering why this error is popping up. It's happened while at highway speed 50+ with the engine warm and everything running very smoothly and MPG consistent with historical values.

I clear the code with no issues and engine performance never seems to be impacted.

Gary

 

Did you replace the gasket on the EGR with a new one or reuse the old one? If you didn't replace the gasket, do so, there may be a slight leak around it.

 

Yeah, I replaced it with the new one. I checked for leaks but can't see or feel anything.