Hey fellas, i have a 1996 Concorde and i just replaced the intake manifold gaskets because of rough idling and surging. The rough idle is gone now and i am actually quite impressed with the difference that made. I also did the EGR valve while i had the plenum off because it was much easier to access. I have the 3.5L in mine.
The only problem i have is that it will idle a bit high sometimes and then return to normal. When i put load on it by turning the steering the rpms will sometime shoot up to 1200 - 1500 and then back down. It will then "hunt" around up and down for about 5 minutes until finally it finds the right spot. It will then idle perfectly until whatever time i add load to it or drive it somewhere and park again, which it then will do the same thing as before. If i wait 5 minutes or so it will idle perfectly again. I am thinking the IAC motor, but at 70 or 80 bux i want to make sure that is what i need. Anyone know of a way to check it? I was thinking of unplugging it while it was doing it to see what happens, but not sure if thats a good idea.
Okay so i just umplugged it and it idles perfectly no matter what i do the rpms are pretty stable. I read somewhere that this should shut the car down but it didnt. Kinda strange i think. I might just go buy a new iac after all. Any suggestions? Thanks!
Last edited by hardin800; 11-17-2012 at 10:58 AM..
Reason: tried unplugging it and doing the same thing.
Yeah i've already sprayed carb cleaner around vacuum lines to check for leakes but didnt find any. It actually idles good with it unplugged which led me to believe it is not working properly. Wouldnt a vacuum leak be there all the time though? It idles like new when it idles "right". It used to idle rough and shake before i replaced the gaskets and egr valve/transducer.
Remove the IAC and clean it good. It sounds like it is working, just may be dirty. Use carb cleaner to spray it, and clean the hole it goes in also (just don't flood that area with carb cleaner, you don't want to run THAT much carb cleaner into the intake). Clean the IAC with an old tooth brush or even just a rag, but don't push on the IAC pintle and damage it - it isn't supposed to be moved any way other than with the motor's power.
Thanks for the input! I am going to try a new IAC in a couple hours. The company i work for has an account with NAPA so i can get one a little cheaper than expected. I will be sure to post the results.
Allright so the new IAC done nothing to improve the stupid idling issue. I am at a loss even after reading hours of peoples ideas on here and other websites. I sprayed carb cleaner all over the damn place (lucky I didn't blow myself up) but still no change that I could notice. The only thing I could do now is the TPS or MAP sensors but I don't see the point of throwing any more parts at it when it's probably not gonna do any good. It seems to be a common problem with these vehicles with no obvious solution.
Anyways, there certainly does seem to be a lot of air getting in somewhere, where I don't know. I doubt it's the intake gaskets again - they are only a month old yet. Also, when I had the intake gasket leak it was shaking and idling very low and rough. Now it idles smooth but fast, then normal, fast, then normal.
I will post what the dealership finds. At $140 per hour they better figure something out!!
I just did an upper and lower intake set on my 3.5 in September, and as careful as I was, I know I still have a bad leak in the lower intake, passenger side, front runner... I sprayed carb cleaner on it while it runs, and you can hear it sipping the liquid in and smell it burning. So, you might look at spraying some cleaner at it while it runs, and see if you hear 'sizzling' as it sucks the liquid in.
Did you disconnect your cruise control servo? I can get you a picture, but just before mine started to accelerate when it chose, it would do EXACTLY what you are describing! Disconnect it, and drive happy! If you find this to be your problem, you can always check ALL vacuum lines going to this servo, or just replace all of the lines, and the servo as a set, just to be safe.
No i haven't tried that, but the cruise control works fine. I used it this morning on my way to work actually.Anything is worth a shot though. What did you disconnect on it? I will have a look at it in a few hours. Thanks!
BTW everything seemed to be working fine coming to work, but thats how it is. It will be good sometimes and crazy other times lol
Last edited by hardin800; 11-18-2012 at 10:39 AM..
Here is an update for anyone who is interested. My Concorde is now working perfectly and has been for 2 days now. I still took it to the Chrysler dealership for a check-up and it passed all tests and no vacuum leaks. The mechanic there told me that I should of waited about a week or a few hundred kilometers after replacing the IAC so the computer can have time to learn. I wasn't aware that the PCM would have to "learn" after a new IAC was installed and I was a bit skeptical on that theory. However, it is running like new now completely so I did something right I guess.
I want to thank all the people on here for sharing their ideas and scenarios on this site. This car was a piece of crap when I bought it and now it is an awesome ride and I love it. So a big thanks to you all!
I don't think that the computer has to learn from the IAC - but I guess there could be something having to do with the time it applies to the motor being different for each motor - as each motor will run a different amount of time for a given distance of the pintle to travel...
Yeah you have a good theory there. I know when I first installed the new IAC the RPM's shot up to around 2000 and then slowly dropped to normal (about 30 seconds). That was likely due to the new IAC being factory set at the wide open position and it took some voltage to close it down. It did act weird for a few days after though idling up and down, but slowly improved. It is perfect now though, and if the Chrysler guys are honest enough to say it's good then it must be I think.
I was expecting them to tell me I needed all sorts of stuff.