idle surging!!

[Rashwerd]

yes yes yes before you say i need to read up i already have went through the FAQ's and the testing to check for problems...problem is when going through the steps it says when i unplug the IAC the engines rpms should stabilize..well mine does nothing also does nothing when i d/c the tps i can remove the CAS and the car will want to die meaning (it works) i have replace the tps already (with a used one) no difference put in a different IAC and it made my idle go to 3k so remove and put the old one back in...so im clueless as to what i should do from here... one thing i seen that was never mentioned as a potential problem is the ECU (computer) does anyone know if possibly the computer could be causing this..? also while trying to solve this minor setback ive been looking at turbo upgrades etc.. are the EVO 3's that are on e bay the real deal or a cheaper knock off type.. any and all help is appreciated thanks.

 

[megadan]

I think that the problem was maybe your IAC. Once you swaped it, you should have adjust your idle and see if it works. Check for vaccum leak too.

 

[sniver]

Mine is doing the same thing, but only when its in motion....so it's real hard to pinpoint anything. Yours surges when stiil, right? I can stabalize mine by unpluging tps, idle switch , I'm not sure about the Iac

 

[top_end95]

http://www.dsm.org/how-tos/tttt/tttt3.html
http://www.vfaq.com/mods/wayback/BradBauer/engine/surge.html

Go through the steps exactly as described. Youre replacing parts without knowing if they're really at fault and you could be replacing a perfectly working unit with a faulty one.

 

[4BangR-x]

according to the OP, he already did.

 

[steve]

y
One thing I've never seen mentioned as a potential problem is the ECU (computer) does anyone know if possibly the computer could be causing this?

The actual surging is caused by the ECU. It sees that the idle speed is too high for the programmed conditions and it cuts the fuel causing the idle speed to drop below the threshold so it turn the fuel on again and the idle rises until the cycle continues. The problem is caused by whatever make the car idle higher than it should. That's usually too much bypass air but too much fuel or timing can also cause the engine to idle faster than normal. Both the IPS and VSS are additional inputs looked at by the code in the ECU related to this problem.

There are three parts to the ISC system, the ISC motor, the ECU and the wiring harness between the two. Any of these or multiples ot these can be broken. A shorted ISC motor can blow the drivers in the ECU so that even with a good ISC motor the ECU can't move the pintle. Where the car will idle with any givern ISC and a bad ECU or wiring depens on where the pintle last was before when it was working.

It doesn't take much extra air to cause a problem. Think about how much difference a small change to the BISS makes when the ECU isn't correcting with the ISC.

Steve

 

[agarcia892003]

i seem to have the same problem...could a bad MAP sensor cause the car to do this too??

 

[1Gdsmdriver]

I had the same problem as did my brother it turned out to be the MAS you might want to look into testing that. I changed to the maft.

 

[dyno_detour]

Did you try adjusting the BISS screw?

 

[gernoff]

These cars are very sensitive to leaks.......Any leak.......As I got rid of more an more leaks the idle steadily improved.

 

[JayRolla]

My car surge's only when warming up and then usually goes away once warm. Sometimes it will start to surge when idleing warm but not much. when it does surge when warm ill be sitting and the idle will be steady then all of a sudden it will rise and start surging. Why would my car work surge then stop? I noticed one day I took the recirculation tube off the bov, while is was running, and it stoped all surging. Why would that have an effect on the surge?

 

[3rdgear]

My car has a problem between 1000 and 3000 rpms. Inbetween the two it tends to jerks the whole car. When its above or below its fine. I was wondering if anyone knew what the problem was and how I could fix it.