Hi guys, seem to have a problem with the idle after warm up.....Will bounce between 650 rmp and below that...almost stalling...I cleaning out the bore where the IAC valve is and replaced the IAC with a new one. I also checked my TPS voltage and it is good at .54 volts. Have a new O2 sensor as well...The timiing is set to 10 degrees (have a gm crate motor(30k on the new motor) says to set it at 10 degrees I have had it there and had no problems). all that said , when I start the car cold it idles at around 1200rpm then it will come down to 650 after a minute or so(is that normal?). Also before the new IAC and cleaning I would have to keep my foot on the gas at a stop light or she almost would die...now I dont always have to do that, it will hold the idle at 650rpm but other times it would drop low and I will have to step on the gas to prevent the idle bouncing up and down... ...havent adjusted the idle stop screw yet could that be it??. idle is out of whack?


My fuel pressure is set at 49 psi ( hose disconnected)

after those changes mentioned above the car runs amazing..stronger and better than before but the pesky idle keeps bouncing when warm..cold she idles like a rock at 1200rpm then comes down to 650 in park..when driving around after cold start up it stays steady at 650 then will start to bounce after warm


I have my upper hose on the throttle body (passenger side)disconnected and have a block off due to the paxton super charger.this hose was oroginally routed from the passenger valve cover to the air filter but I took out the hose going to the air filter and have air breather valve on the passenger valve cover now..could this be causing the bouncy idle??--no hose from the valve cover to the throttle body


help..idle is driving me crazy

 

I'm having the EXACT same issues and got in here to see if anyone could help. I'm leaning towards the ESC module at the moment, that or the ignition module has to be what's going on. Mine also will sound like it's backfiring through the exhaust but only at certain throttle positions and around 2500rpm, VERY weird.

 

In my experience, disconnecting the regulator will produce too rich a mix at idle and light throttle. This may be a contributor. Also, setting minimum air (if you havent done so already) is a must. If you can, connect a scanner up and see what the sensors are doing. Also, check for vacuum leaks. around the intake and accessory hoses.

 

Hi Detroit, my regulator hose is connected..havent adjusted the minimum air yet...I have a scanner(autoxray)..Checked for leaks everything looks oK...only after when the car warms up it will start to bounce...

afer changing the AIC as mentioned earlier the idle is awesome when cold...stays at 1200rpm then it will come down to 750 rpm...but after warm up it will start to hunt.....

 

I would set minimum air before I get too crazy, it may fix the problem and it's free. What does your scanner say that things like timing and IAC steps are at when this happens? If the IAC is too far either way it won't be able to control the idle properly and it will vary. It seems like you covered most of the big things, but due to you being supercharged I may be missing something- maybe one of the S/C guys will have some tips as well!

- Also, make sure Coolant temp and throttle position are reading Ok, and not varying. One other thing might be checking the vacuum line to the MAP, a little hole here can really screw stuff up.

 

hey i'm having the same problem i've asked quite a few experienced people about it both on this site and off and to me it seems to be electronic i believe one of the sensors is bad at least in my case... my car does the same thing except will stall... i had my uncle who used to race and my grandfather who used to drag and they believe its not a mechanical problem because the jumping of the idle is the car attempting to correct itself my uncle said there are a couple oxygen sensors and other sensors that deal with the idle and low rpm he said one of those are prolly bad... my solution is im going to buy a program my grandfather told me about to do my own diagnostics on the car which should tell me what sensor it is right away...

 

i've been told all the stuff above about the iac, maf or map, throttle body, this airflow, that but none of it fits because the problem isn't sparatic like it would be if there was a hole in the vacuum lines or i wasnt getting the right air flow.. agreed? the MAF/MAP is easy enough to check just unplug it but if you are having the same problem i am thats not it...

 

I'm thinking about putting in a heated 02 sensor since I have long tubes. If I understand correctly you have to jump the AB connectors and put the car in diagnostic mode to set the minimum idle, this is an issue since my cars ALDL port didn't match up (MAF TPI engine in a TBI car) and no one seems to know what wires I need to run from the ECM to a new ALDL connector. Can I just unplug the IAC and set the minimum idle that way like a Mustang?

 

You cannot set minimum air by just unplugging the IAC; the computer must have terminals a and b jumped or the IAC will be partially open.

Irockaniroc, it sounds like you need to look at your car with a scanner when the problem occurs if possible; just unplugging sensors isn't quite adequate - you have to look at the sensor's values, otherwise, it's all shots in the dark. You can just about rule out the O2 sensor, it won't kill the car- the computer will stop looking at it if it goes bad. Also, set min. air and throttle position if you havent already. Cleaning the throttle body might help too.

You can check most top end mechanical conditions by using a vacuum gauge, your uncle or grandfather could probably show you how to do this- it's about the same it was back in the day. I once saw an intake valve chip and send all kind of goofy MAP signals on a 5.0 Ford, after screwing around with it for a while we finally diagnosed it with a vac. gauge.

 

That makes it even more imperative to get this ALDL wired... I hate forced motivation.

 

Hi guys, finally fixed!! Just had to set the the minimum idle air ...Guess it was off....idles in drive without bouncing..also had to re -adjust the TPS due to the new setting...Now just have to take it for a drive tommorrow and make sure it is all good.....thanks for all your responses

 

how do u go about setting the min idle air cause maybe thats whats up with mine too... and thanks 4 the tips detroit..

 

No problem, glad to help- if you look in the tech articles section of this site you'll find a page, I think it's called 'IAC Adjustment' or something like that. Don't forget to reset TPS voltage as well, there's a page on that too.