funny idling problem

[townethug]

So Saturday night I drove my car all night with no problems. Sunday morning I come out and start up the stang and she starts doing this surging idle thing. I let it run for a couple of minutes and it gets no better. So I turn the car off and start it back up. The problem is completely gone, and it ran fine. Later on that day I start it up and it starts the surging idle again. This time its not as pronounced as before but def not running smooth. So I shut the car off and start it again and like magic the problem goes away. Then later that evening I start it up and of course its surging again. Only this time no combination of turning it on and off has fixed it. I let it get warm to see if this sovles the problem but it didnt appear to or atleast not all the way. The surging sort of leveled out but it was still running rough, like it was missing. It got up to about 170 degrees, so i figure if its not running by then its not going to. My current thought is it could be a spark plug going bad or maybe some senor. I figure before I start replacing random things, see if anyone else has opinions or experience with this sort of thing.

much thanks.

 

[AnthonyR23]

I would do a engine off diagnostic test for codes... then once you fix those.. do a engine on test for more codes.. If you search on this forum for best diagnostic tester for the money.. I wrote about doing the testing with test light and paper clip or tweezers... after doing the tests... another thing to check is your vacuum.. with a vacuum gauge and a piece of vacuum line.. check the blank capped off spot on the vacuum distribution block on the driverside firewall... what vacuum are you pulling at idle... Mine is about 22psi.. If you have cleared all error codes and you are pulling the correct vacuum.. then you could try taking off your idle air control motor on the side of the throttle body and give it a good cleaning....

what rpm is your car idling at with the iac..(idle air control motor) unplugged? The The iac is on the front of the throttle body towards the front of the car.. you'll see the plug dangling there.. just unplug it and the car should idle lower... should idle at about 600 without the iac plugged in.. when it is plugged in the computer should adjust the idle to the right level.. If it isn't idling at 600 you can adjust the screw at the bottom of the throttle body to try to bring it down to 600.. but if you do that make sure you adjust your throttle position sensor at the top of the throttle body.. with a multi-meter positive to the green wire and negative to the black wire.. don't use the body as a ground... with the key in the run position you should be getting anywhere from. .6-1.16 voltage or .6-1.0 if your tps is out of range one of the error codes will come up..

 

[townethug]

Thanks for the post. I went ahead and ordered one of the Equus testers. I figured for 30 bucks, why not, atleast this way I dont have to translate flashes into numbers, plus i dont have a test light. I hope to have the device soon, with in the week. I will post the codes as soon as I can. Thanks for the help this far.

 

[jrichker]

You guys with idle problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first post has all the fixes, and steps through the how to find and fix you idle problems without spending a lot of time and money. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix!