This something I've already found the cause, but am unsure of just WHY it causes the surging.

A couple of months ago I did a pretty extensive upgrade, though sadly I couldn't afford some really nice heads I went with what I had.

When it was all put back together it had some major surging issues while at idle and part throttle. But the funny thing is the problem only persisted in closed loop with the air bellows and filter off....

I had the throttle body to MAF bellows on, the Maf is connected and plugged in. But without the rest the air filter and bellows it just doens't idle that well at all. Put the rest of the air filter setup on and it idles just fine, only varying by 50 to 75rpm from the target idle of 650.

Could it be that without the air filter the MAF sensors air flow was too turbulent to get a good measure? I suppose I should get a datalog of it idling both with and without the air filter.

I don't want to build a cold air intake just for it to act like that.

 

in closed loop.. you're getting too much air in closed loop to support the amount of fuel its being fed. your engine is "surging" because the computer is trying to balance the table out.

you need to check out your tables in the chip when its closed loop.

OR

my other suggestion is.. leave your air stuff on. no need to run the car with it off if its running fine with all the correct things hooked up properly

check for MAF codes in the system

 

Actually is the duct between the MAF and the Filter that helps maintain the airflow straight. Without it the air will be sucked around the sampling tube and the ECM goes crazy because of the erratic signal, hence the continuous surge. (I've done this same test)

If you are going to build a CAI keep the MAF to TB duct as is. The distance between them is optimized and you should stay within 12 inches of the TB if you are going to build your own. The duct between the MAF and Air Filter can be longer but remember to keep all turns smooth to avoid problems with the MAF or internal drag.

-Ozzy

 

I HAD THE EXACT SAME PROBLEM!

Throttle Position sensor, unplug it and if it stops go buy a new one. Fast fix

 

You just said what i was trying to say earlier. Only you said it much better!

What you described is exactly the symptoms I had. Putting on the air filter and every as it was factory fixed the whole problem.

Now its time to gut the air box. ^_^