Intermittent idle issue??????


Sep 28, 2004
okay i have this idle issue that i just can't figure out. my car will run perfect at times and you wouldn't know there was anything wrong with it, but other times the idle will keep jumping as high as 1200 all the way down to almost zero and it stalls sometimes. i can play with the gas and sometimes the idle evens out and it stays perfect at about 650-700. i have checked just about everything i can think including the maf, the tps, the iac is new, the timing is good and i can't find any vacuum leaks. i replaced the tfi module about a year a so ago and it seemed to help the idle issue i was having at the time. it has since came back and is getting worse but sometimes i can't keep it running and other times it runs perfect. i can let it idle in the driveway when it evens out and it will run forever perfect until i hit the gas. this is a major issue in town when i stop at lights the idle just starts jumping so much that is stalls out at times. if anyone has any input on this let me know.

my setup

347 stroker with anderson n-3 cam old grind (2500-6000 range)
gt40 tubular intake
roush 200 cast iron heads
mac long tube headers, full 2.5" exhaust with h-pipe
70mm tb
cai fenderwell
76mm c&l maf calibrated for 24lb inj
24 lb injectors
t-5 manual
3.73 gears
stock distributor with accell cap and rotor, replaced tfi with used....worked for a while, not sure how to check to see if it's bad
new ford racing wires
new ford racing coil
msd 6a just fixed by msd last year
new plugs last year
new iac last year, coolant temp sesnsor
timing is base 10 degrees
dyno tuned at RJ Dyno shop batavia ny, 2005
NO CHECK ENGINE LIGHT!!!! (it works i check it)

Any help would be appreciated because i don't want to take it in if i don't have to, thanks.
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Sep 28, 2004
problem found and resolved

i have been battling with my mustang running right for years and finally last week the culprit was discovered. i finally fixed all the issues with the car including the ignition , plugs and sensors and i took it to the dyno for some tuning. i got my car all tuned up and it got great numbers surpassing my goals and i drove it home and it seemed wrong. the car wouldn't idle or even stay running, so the next day i took it back to the shop and told my mechanic what was up. he worked on it for over 4 hr. and did several more dyno runs and discovered a wire going into the ECU was corroded. The ironic thing about this was it wasn't an obvious thing because the corrosion was black and was hidden between the wire and the plastic casing. with all said and done the car runs amazing now and the idle is perfect. so if you are scratching your head, and you think you have tried everything odds are there could be an ECU issue or like in my case a wire issue that connects to the ECU. i never would have found this so kudos to my mechanic for putting the time in and i was glad to pay for the work. i hope this info. helps somebody. i will post a video and dyno graph asap when i get them onto the computer.


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Mar 10, 2000
Dublin GA
Wire color and number would help the rest of us...

The following is a view from the computer side of the computer wiring connector.


Active Member
Jun 7, 2003
Akron, OH
650 seems a bit low to me for an idle mine idles at 800-900 try bumping it a but see if it helps. Intermittant problems suck. C&l meters suck btw, this cure all my drivabilty issues by getting a Pro M meter.


Sep 28, 2004
idle issue fixed

hey i recently had my car dyno'd and spent quite a bit of money, but it was worth the time and money spent. the idle is fixed and the problem was a wire going into the cpu, a grounded wire that is. the guy who dyno'd the car worked on it for about 4 hr. and found there was a bad wire going into the computer, and i'm sure this was the culprit of my issues for sometime and i was replacing and checking everything else. oh how i hate electrical issues. well thanks for the good info. and the post about the cpu wiring.... good idea, that was the problem. i hope this thread helps someone out. car runs sweet now at the 6-700 rpm idle.