terrylange Posted May 14, 2009 Report Share Posted May 14, 2009 I noticed a few weeks ago that when I started my 2001 DTS (140K) in the morning, sometimes the higher idle speed wouldn't kick in for the first 30 seconds or so like it had always done in the past. When this happened, the car would stall either immediately or as soon as I put it in gear, or if I stopped within the first couple of blocks. I figured the throttle body might be the problem, so I spent some time cleaning it out. Since then, the idle speed has been all over the map. Some days, I can take my foot off the accelerator and maintain a speed of 50 mph for 5 miles. On a single occasion, it was reving so high I had to shut the car off while it was still in gear. Other days, it operates perfectly, with the normal fast idle at start up, slowing down after a short warm up. I have to emphasize that this problem is intermittant, so I don't believe I damaged anything while cleaning the inside of the throttle body. I looked at the shop manual, and there is a lot of info on something called the "Idle Air Control (IAC) System." Properly testing this component requires connecting a J 37027-A IAC Motor Driver to the IAC valve. Coincidentally, I don't happen to have one of these in my tool box!! Does anyone know if I should just order and replace the IAC valve (it appears to be a simple procedure), or am I barking up the wrong tree? Thanks in advance for any help. Terry Link to comment Share on other sites More sharing options...
adallak Posted May 14, 2009 Report Share Posted May 14, 2009 Terry, As a member with 73 posts you should know that it always helps to pull any storred trouble codes. The saddest thing in life is wasted talent Link to comment Share on other sites More sharing options...
terrylange Posted May 14, 2009 Author Report Share Posted May 14, 2009 Terry, As a member with 73 posts you should know that it always helps to pull any storred trouble codes. Link to comment Share on other sites More sharing options...
terrylange Posted May 14, 2009 Author Report Share Posted May 14, 2009 Terry, As a member with 73 posts you should know that it always helps to pull any storred trouble codes. Link to comment Share on other sites More sharing options...
terrylange Posted May 14, 2009 Author Report Share Posted May 14, 2009 Terry, As a member with 73 posts you should know that it always helps to pull any storred trouble codes. Link to comment Share on other sites More sharing options...
terrylange Posted May 14, 2009 Author Report Share Posted May 14, 2009 After I hit the "send" button, I realized that I hadn't commented on any trouble codes. The only codes showing are all HX codes, and are intermittant ABS and suspension related codes that I have been living with for quite some time. There are no new codes displayed that would correspond with my current idle speed problems. Terry Link to comment Share on other sites More sharing options...
Jan Olsson Posted May 14, 2009 Report Share Posted May 14, 2009 After I hit the "send" button, I realized that I hadn't commented on any trouble codes. The only codes showing are all HX codes, and are intermittant ABS and suspension related codes that I have been living with for quite some time. There are no new codes displayed that would correspond with my current idle speed problems. Terry It sounds like the kind of trouble I was having (keeping my fingers crossed it won't come back again). Various sensors/components can put the idle speed out of whack. MAP, MAF, IAC (or ISC) and TPS. All of the mentioned components have internal diagnostics but in the case of no codes it seems like it is common that the TPS is bad. Test to plug and unplug the connector 10 times or so. It is the best way to give it a rinse, it can also be connectors misaligned, cables with kinks etc. I bought a new IAC-valve and a new MAP because the idle speed and quality improved when playing around. To no avail..Now I tested to pull and reconnect the TPS connector and it seems alright..but it can also be the sensor itself going bad. They seem to develop a "dead spot" Link to comment Share on other sites More sharing options...
Ranger Posted May 15, 2009 Report Share Posted May 15, 2009 Don't overlook a ripped plenum causing a vacuum leak. Very common on 2000+ Northstars of some age. Link to comment Share on other sites More sharing options...
Jan Olsson Posted May 15, 2009 Report Share Posted May 15, 2009 Don't overlook a ripped plenum causing a vacuum leak. Very common on 2000+ Northstars of some age. Yes. But can a vacuum leak really cause fluctuations in idle speed or rather an intermittent high idle? Seems like an electrical problem? Link to comment Share on other sites More sharing options...
Ranger Posted May 15, 2009 Report Share Posted May 15, 2009 I think I recall hearing of them causing this. I know it does not sound logical, but it is easy enough to rule out and should not be overlooked. Link to comment Share on other sites More sharing options...
Jan Olsson Posted May 16, 2009 Report Share Posted May 16, 2009 I think I recall hearing of them causing this. I know it does not sound logical, but it is easy enough to rule out and should not be overlooked. I hear you. Guess I better check my plenum gasket too Link to comment Share on other sites More sharing options...
growe3 Posted May 16, 2009 Report Share Posted May 16, 2009 I noticed a few weeks ago that when I started my 2001 DTS (140K) in the morning, sometimes the higher idle speed wouldn't kick in for the first 30 seconds or so like it had always done in the past. When this happened, the car would stall either immediately or as soon as I put it in gear, or if I stopped within the first couple of blocks. I figured the throttle body might be the problem, so I spent some time cleaning it out. Since then, the idle speed has been all over the map. Some days, I can take my foot off the accelerator and maintain a speed of 50 mph for 5 miles. On a single occasion, it was reving so high I had to shut the car off while it was still in gear. Other days, it operates perfectly, with the normal fast idle at start up, slowing down after a short warm up. I have to emphasize that this problem is intermittant, so I don't believe I damaged anything while cleaning the inside of the throttle body. I looked at the shop manual, and there is a lot of info on something called the "Idle Air Control (IAC) System." Properly testing this component requires connecting a J 37027-A IAC Motor Driver to the IAC valve. Coincidentally, I don't happen to have one of these in my tool box!! Does anyone know if I should just order and replace the IAC valve (it appears to be a simple procedure), or am I barking up the wrong tree? Thanks in advance for any help. Terry You say the "...Since then, the idle speed has been all over the map...". That would indicate that you did something to effect the problem, The question is what was it that caused an effect, sounds like it got worse. I would advise taking off the air cleaner and give the throttle body a good visual. Looking for and/or loose or pinched wires, pull gently on the wires and vacuum tubes in this area, one may be loose or cut. The throttle plate should seat completely with the engine off, work it a few time to verify this. Start the engine with the air cleaner off. Does it run OK? Does it idle properly? quick rev, does it slow down within a few seconds? If these test seem OK, carefully put the air cleaner back on, and then restart. The engine should run the same as with the air cleaner off. If it doesn't, you may be putting the air cleaner back on wrong or jamming some connections. -George Drive'em like you own 'em. - ....................04 DTS............................ Link to comment Share on other sites More sharing options...
terrylange Posted May 18, 2009 Author Report Share Posted May 18, 2009 Thanks Jan, Ranger and George for your suggestions. It has taken me a while to get back to you since I generally drive my car to work on Monday and leave it there for the week. I was intrigued by Ranger's comments on a leak in the plennum, so I took it apart again at work earlier this week. While I did not find any cracks in the plennum, I did note that in reassembling things a few weeks ago after cleaning the throttle body, I may not have lined everything up properly, which could have allowed for some air entry into the system (wishful thinking?) Anyway, I re-aligned everything and checked for a tight fit. I started the car up then, and again this afternoon, and found that immediately upon starting, the idle speed is low, but picks up within 2 seconds to the stepped up speed, then it drops down again after about 30 seconds. Aside from the initial hesitation, this appears to be where things should be. I drove the car home this evening, and didn't encounter any abnormal variations in the idle speed. I'll take it out again tomorrow, and will keep my fingers crossed. I always like repairs that don't cost any money. Hope the fix was as simple as this!! Thanks again, guys. Terry Link to comment Share on other sites More sharing options...
flatback2 Posted May 18, 2009 Report Share Posted May 18, 2009 If you have not done so already I would clean the throttle body. It's cheap and easy and I am always amazed what impact this simple procedure produces. Link to comment Share on other sites More sharing options...
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