Guest 2fit661ca Posted July 24, 2011 Share Posted July 24, 2011 My 97 LeSabre has 199,500 miles on her and has an erratic idle. When at idle, it bounces around a range of about 100 rpm or so and can't idle steady. My fuel gage doesn't work, so every time I put gas in, I fill the tank. Everytime I start it after filling up, it consistently goes up to 1600, then down to 400, then up to 1300, then about 600, and slowly evens out until it reaches it's normal erratic idle. The erratic idle goes away the moment I put any pressure on the gas pedal. Any ideas what could cause my problem? I'm going to try the fuel filter, pcv valve, plugs, and other cheap maintenance that needs done either way and I will report back. THANKS!!! Link to comment Share on other sites More sharing options...
JohnD1956 Posted July 24, 2011 Share Posted July 24, 2011 There is an idle air control on the throttle body. If I remember right, when you look at the throttle body from the front towards the windshield, it is the rectangular black box directly in front of you. If you remove the air tube from the aircleaner housing to the throttle body what you may find is the inside of the throttle body is coated in a black tar like substance. While the inside of the throttle body throat can be cleaned with carb cleaner, you do not want to spray carb cleaner into the port just below the idle air control ( IAC) . There is a spray made specifically for the IAC, and you want to get some of that and follow the directions to degrease that sensor. Then you want to spray the rest of the throttle body throat while the engine is off, capturing any run out with an old rag for disposal. If your idle is still eratic after that I would suspect the EGR valve. Hopefully that's not one of those electronic ones like the 89 had which seems to cost a lot of money. Link to comment Share on other sites More sharing options...
NTX5467 Posted July 25, 2011 Share Posted July 25, 2011 (edited) I concur that it's probably related to the IAC and related passages. The reason the speed becomes more consistent when you barely touch the accelerator pedal is that the throttle valve will then be controlling the air which enters the motor rather than the IAC circuit. To me, that would certainly point to a clogged and/or malfunctioning IAC situation. At idle, the main throttle valve is fully closed, unlike in a carburetor where the idle valves are partially open at idle.When the EGR valve is not properly closing at idle, it can cause a fast idle situation, which the IAC will also try to control. When it can't it should set a code. But it should usually be a uniformly high idle speed, rather than one which varies and then settles-in to a slower speed.In some cases on some GM engines, the throttle body can't be successfully cleaned and must be replaced. I don't recall this being one of them, though, so I'd try an effective cleaning first, even if it might take a few times to get everything out. Sometimes, there can be solid carbon deposits in there, which probably would need to be removed "mechanically".Once you have the throttle body and all IAC passages and motor cleaned up, don't forget to continue the cleaning with the air supply pipes/lines too as if there's stuff in the throttle body, there's probably "stuff" in the lines which bring the air to the throttle body/IAC too.Just some thoughts,NTX5467 Edited July 25, 2011 by NTX5467 (see edit history) Link to comment Share on other sites More sharing options...
TxBuicks Posted July 25, 2011 Share Posted July 25, 2011 I had the exact same issue with my 1991 Roadmaster, which has the throttle body injection system. It would idle very fast at startup and gradually calm down, but at stop lights it would surge forward to the point that I had to hold the brake pedal down with a lot of pressure to keep it from lunging forward. Changing the EGR fixed it. It is relatively inexpensive (mine was $85) and easy to replace, and if you've never changed it, it is due. Try that first. Link to comment Share on other sites More sharing options...
Guest 2fit661ca Posted July 25, 2011 Share Posted July 25, 2011 I changed the EGR valve last winter after a misfire MIL detected that to be a problem. The old valve had huge amounts of carbon build up, so it would only make sense for the throttle body and the IAC to have that as well. I don't know why I didn't think of that. And when I replaced the EGR valve, I just paid the $190 for the life time warrenty Borg Warner valve so if it needs replaced on the road, i just need to find an o'reilly's. THANKS FOR THE HELP!!!! I will check it out friday when i get out of work. (full time job and school doesn't leave me much wrenchin time) Link to comment Share on other sites More sharing options...
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