What can cause on even idle??????


Oct 6, 2004
Hi guy's i have some problem's with the idle on my car , when i start it it runs fine for a while and then you can hear a slight jump in idle not to much and then after 3 sec get's back to normal and every 30 to 20 sec of idle does this any ides????????? :shrug:
it's not ideling even all the time like it should :(
and also from time to time the rpm drop's at idle to like 400 or 500 that makes the car run rough for like 4 ,5 ces and go'es back to N
what the hell what may cause this :shrug:
please help
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I'd check for the obvious stuff like v leaks, bad electrical connections, and the like.

Is this something that just started all of a sudden or has it been geting worse and worse?

Are your K's holding steady and close to 1.00?

Honestly ... it could be several different things. But if I had a problem like yours, I'd definitely start with that IAC valve. Clean that puppy out with carb cleaner or TB cleaner. The link that Bill provides shows you how to do this.
Agreed. Remember, the computer can raise the idle but it cant lower the idle. A surge can be the idle going low due to any number of reasons and the puter jumping it back up.

I would also go through that link and clean and reset the components and see what it does. If you start playing with the throttle stop screw and idle bleed screw, keep scrupulous notes so you know what you did. I make the turns in 1/2 turn increments and have a log of the turns in the front cover of the manual.

Good luck.
The only thing i have to check or replace is iac and the TPS (is tps adjustable on our cars????) :shrug:
The T body is New and still nice and shiny inside out :D
My maf is also new i have it for few week's now :)
the weather is getting nicer here so it's time to get under the hood :nice:
if i get all the things done and double check and problem still exists then what's next?????

You have a TwEECer, so you want to tune your TB and MAF in. Start with the TB by datalogging an idle with the ISC unplugged and spout removed. That will tell you what your TB is flowing (you need to multiply the average MAF (kg/hr) by 2.02 then divide by 60 to get that number. Then you enter that in the 'Throttle Body Air' scalar.

BUT if you want to be lazy . . . start by adjusing the TB screw to like 3 turns open then change your 'Throttle Body Air Flow' to something more like .7-.85. The go to the 'ISC Neutral Idle Air Flow' function and increase all the Y-values by about 25%. That should give you a starting point for what you want to mess with for a decent idle. Your goal is to get the car to idle at the target idle that you set in the scalars while maintaining about 30-40% ISC duty cycle (ISCDC in the log file)