rrdrerup115 Posted December 6, 2004 Report Share Posted December 6, 2004 I have a 1999 STS and it will occasionally stall. The Service Engine light is on, and the codes I'm getting are for MAF Sensor Circuit Low Frequency and MAF Sensor Circuit high Frequency, along with the obvious Stall and Near Stall code. I replaced the MAF Sensor and the problem persists. I have cleared out the codes, and they will reappear. The car has stalled under various conditions, cold, hot, city driving, coming off the highway...but it does seem to always be when I'm coasting. It will restart after a few seconds. Any ideas?? Thanks! Link to comment Share on other sites More sharing options...
Ranger Posted December 6, 2004 Report Share Posted December 6, 2004 If it were just the stall problem I would guess at ISC (idle speed control valve). Perhaps the two are not related? Just a shot in the dark. Link to comment Share on other sites More sharing options...
JohnnyG Posted December 7, 2004 Report Share Posted December 7, 2004 I am leaning toward the ISC as well, but if it were bad, I would think it would also set a code. Maybe the throttle body needs to be cleaned as it could be sticking closed and not allowing the ISC to "crack" the throttle when needed. Could you list the codes you are getting. Does anyone know why the "frequency" goes high or low on the MAF sensor? Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
adallak Posted December 7, 2004 Report Share Posted December 7, 2004 Do a simple test - retract the ISC motor plunger completely so that it does not touch the throttle lever. For my car it may be done thru override mode and pressing Cooler button and unplugging ISC. If engine stalls at operational temperature - it will stall most likely while coasting since the blades are at minimum angle. Cleaning TB thoroughly never hurts and maybe all what the doctor prescribed. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
Ranger Posted December 7, 2004 Report Share Posted December 7, 2004 Correct me if I am wrong, Adallac, I don't think the Northstar has an ISC motor like the 4.9. I think it is an ISC valve similar to the pintle valve on the EGR. JohhnyG, If I am correct the ISC valve is a bypass circuit meaning it controls the amount of air neccassary for idle behind the throttle plate and therefor unlike the 4.9 does not move the throttle plate for idle. Maybe the ISC valve is sticking or seat is dirty. Just a theoretical guess as I have never fooled with one. Link to comment Share on other sites More sharing options...
adallak Posted December 7, 2004 Report Share Posted December 7, 2004 Adallac, I don't think the Northstar has an ISC motor like the 4.9. I think it is an ISC valve similar to the pintle valve on the EGR. Ranger, I do not have idea, but would not be surprised if GM came up with something better than ISC motor The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
JimD Posted December 7, 2004 Report Share Posted December 7, 2004 Adallac, I don't think the Northstar has an ISC motor like the 4.9. I think it is an ISC valve similar to the pintle valve on the EGR. Ranger, I do not have idea, but would not be surprised if GM came up with something better than ISC motor But GM did it...... Jim Drive your car. Use your cell phone. CHOOSE ONE ! Link to comment Share on other sites More sharing options...
JohnnyG Posted December 8, 2004 Report Share Posted December 8, 2004 Correct me if I am wrong, Adallac, I don't think the Northstar has an ISC motor like the 4.9. I think it is an ISC valve similar to the pintle valve on the EGR. JohhnyG, If I am correct the ISC valve is a bypass circuit meaning it controls the amount of air neccassary for idle behind the throttle plate and therefor unlike the 4.9 does not move the throttle plate for idle. Both of you guys are probably right. I never had one apart on my '99, but the pintle arrangement sounds very similar to my '86 Merkur. On THAT motor there was a setting procedure that required the throttle position sensor to be set so it produced exactly 1 volt at proper idle speed. Going through that procedure BY THE BOOK corrected all of the idle problems. Cleaning the pintle or ISC VALVE and throttle body is probably the first thing to do. Followed by a by the book adjustment of the throttle position sensor. Also, if there is a throttle position sensor that is similar to a wire wound rheostat, it could have dead spots on it, particularly near the idle position, contributing to the problem. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
TAB Posted December 8, 2004 Report Share Posted December 8, 2004 I have a 2001 STS. I had mine ocassionally stall sitting at a light. It would start back up with no problem. I had no check engine light. Under warranty the dealer replaced the Crankshaft Postion Sensors which they said were shorted and the problem never came back! Not sure if this is the same problem, thought I throw it out there! Link to comment Share on other sites More sharing options...
JohnnyG Posted December 9, 2004 Report Share Posted December 9, 2004 TAB, I don't suppose you were able to read the codes that were set by the sensors were you? I would think a crankshaft position sensor failure such as that would set its own unique code. I doubt if the two problems are related, but thanks for the input. You never know, maybe a crank sensor can become intermittent..still casing the problem, but not disabled long enough to set a code. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
TAB Posted December 9, 2004 Report Share Posted December 9, 2004 JohnnyG, sorry but I don't have the codes. Since the car was under warranty I just brought it in to the dealer to diagnose. I checked the write up and it doesn't mention any codes that they may have picked up. Link to comment Share on other sites More sharing options...
JohnnyG Posted December 10, 2004 Report Share Posted December 10, 2004 So, rrdrerup115, how are you doing with your problem? Have you had an opportunity to try any of the suggestions made by the members of this board? Have you found the board helpful in any way? I must admit, your problem did not seem to attract much attention. Several months ago, guys would have been all over it. Sorry if this forum hasn't been as much help as you expected. Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
rrdrerup115 Posted December 11, 2004 Author Report Share Posted December 11, 2004 Johnny - I just got the problem fixed last night as a matter of fact, and I DID find the help here very educational. Not just on my post, but all of them. I did not want to dig into the throttle body myself without knowing exactly what to do. I have a tendency to waste hundreds of dollars trying to save 20 so I took it to my trusted auto repair shop. It was the MAF Sensor again! Believe it or not, the one I got from Advance Auto ($125) was bad. My mechanic told me the economy replacements were not very reliable. I got a new one, and put it on after work last night and presto, no more engine light, no more stalls...at least not yet. They gave me my money back on the faulty one. Thanks for everyone who helped trouble shoot this. If it persists, I'm going after the throttle body and the IPS. Link to comment Share on other sites More sharing options...
JohnnyG Posted December 12, 2004 Report Share Posted December 12, 2004 Fantastic! I hoped it would turn out that way, and I'm glad this board helped in some ways. I always felt that this was the best bunch of guys around when it came to Caddys! I hope you and your wife enjoy your new car for many years to come. Most of us on the board will tell you plenty of horror stories about aftermarket parts. And most of us recommend genuine GM parts for that reason. Thanks for the update. JG Never underestimate the amount of a persons greed. Link to comment Share on other sites More sharing options...
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