Hanging idle @ 2k then returns to normal

Hanging idle @ 2k then returns to normal - NOW WITH PICS

So, ive been trying to piece back together my mustang after getting it back from a crappy CRAPPY shop - Details and all accounts are here http://www.stangnet.com/mustang-forums/825593-running-rich-issue.html

Now Im finally getting around to actually finishing it - however another issue has come up. The car starts strong every time, idles perfectly, no hiccups, surging, purs like a lion when im running it now with no exhaust except headers and down pipes - perfect... until you rev it.

It revs strong, fast, dosnt backfire, but then hangs at 2k rpm for 6 or 7 seconds, then drops back down to standard perfect idle.

I drove it tonight after I got the new wheels put on it and it runs strong, gets up quick, but as soon as i let off the gas and put the clutch in, it will hang at 2k rpms for 7 to 8 seconds, kind of an embarrassing amount of time.

Ive read the surging idle checklist - specifically topic 6, about cleaning the 10 pins, However - the car did not have this problem prior to me installing a new A9L ECU from seijirou (for whom i love for being so gracious for ) But seriously, on the 2nd page of the above posted link shows the old ECU, the shop put in an SD ECU to my MAF converted car (out of a ford topaz of all things)

Now that the proper ECU is installed, would it be causing an issue such as this?

Would running it as SD completely bypass the 10 pin connectors, rendering them useless, hiding the fact they may be dirty or damaged?

Would having no exhaust aside from down pipes before they connect into the H (o2's are hooked up) cause issues like this?

Either way, Im driving it to the exhaust shop tomorrow to have them finish putting up the H, installing some new mufflers and tail pipes for my cobra rear bumper.

I should have pics tomorrow

Anyone have any ideas?

After doing more research - showing that the IAC may be a culprit, also a sticky butterfly inside the TB - BUT - this problem just started happening when i installed my A9L ECU

I reallly want to get this thing set for the road, and im SOOO close, i just need to get rid of this annoying problem.

Thanks for any help in advance

No, codes coming back the same as they were last time i ran them at a shop. Just the standard idle one (7 i think - not sure)

I can stop by the shop again after i get the car back today to have them re run and see what pops up with exhaust actually installed

Well... even if the idle stalls at 2k then falls, it will still look pretty Ill be putting up some pictures soon after I pick her up in a few hours and wash her.

Ill clean the 10-pins, inspect for sticking butterfly in the TB... but again, all this started happening after i put in the A9L ECU, so I really dont know what would be causing it other than an ECU problem.

I have larger injectors and a calibrated MAF for them, would that induce this symtom at all?

larrym1961 said:

I did read on here one time that the hanging idle for 5 to 7 seconds after reving the motor up was known as a "Dash Pot delay" programed into the computer to burn off the excess feul. How true that is, I don't know mabe someone here knows that as fact.

Anyway I have just accepted it as that and I live with it.

Click to expand...

Is anyone able to confirm this?

After driving the car a bit more, it dosnt happen that often, however i have noticed that when going around 1500 rpms driving, then putting in the clutch, it will jump the idle to 2000 like it does... Ideas?


AAAANNND as i said, i got pictures of her