Lets compile a list of things that can cause bad idle

[staticc]

since, my new fox has a bad idle, and stalls 2-3 times before it runs good.. then its warm and its fine, but its got a b cam. so that doesnt help...

and, almost every other day, someone posts about a bad idle.

so lets just save everyone and myself the trouble and just make a big list of things that can fix/***** your idle

thank you
derek

 

[Icepick]

Set my idle to 950 and it's almost perfect, at 600 it surged. I'll buy a new MAF soon and hopefully it will help things as well.

 

[stangbear427]

Dirty injectors
Dirty MAF sensor
Bad IAC motor
Bad TFI module
Throttle screw improperly adjusted
Loose distributor
Leaking/loose/rotten vaccuum lines
Bad O2 sensors
Bad cat's
Dirty air filter
Any failing pulleys: H2O pump, air pump, P/S pump

I'll add more as I think of things- anyone else? Good idea, hopefully that "new FAQ on Stangnet" will be up and running soon to help cut down on this stuff. The search function isn't always the greatest...

 

[90silverstang]

Clean throttle body, Idle bypass Valve, Egr valve, PCV valve,, remove throtlle body and disassemble and clean the above. Then adJust throttle position sensor.

 

[staticc]

awesome so far. you guys are great
we need to compile a page on all of this. and have directions on how to set your Throttle position sensor etc

 

[gearheadboy]

VACUUM LEAKS, upper or lower intake gasket leaks cause lean condition which causes rough unstable idle. This can be detected by shooting a small mist of carb cleaner around the gaskets with the engine running, if it smooths up, you found your leak. I have posted before that any Fords that have an Idle speed valve can usually be corrected by removing and cleaning the valve, port, with some carb cleaner. Also the dirty throttle bore can cause this, clean it with throttle body cleaner and a small brush.(carb cleaner is said to eat the coating from the surface and should not be used) Also do not adjust the throttle plate for "idle speed" as this with screw up things. Why? because the adjustment is only to keep the plate from binding, and the Idle air valve computer controls the idle speed. Also Throttle position sensor values will change if tampered with.
With that said, someone that has changed the camshaft such as you, or made other induction system mods, may benifit from tweeking the TPS setting, or the throttle plate base setting slightly to lean or richen an idle mixture. But it will take trial and error and I sugest using a multimeter to read TPS values and record the changes.
Cleaning the secondary ignition system helps rough idles also:
Clean dist. cap contacts
" " rotor contacts

 

[wgungho]

And if all else fails, try this!

Ford makes an Idle Air Bypass spacer, and it's a real cure-all for surging idle on 5.0s due to aftermarket parts, such as TBs, bigger MAF, bigger cam or intake, etc. I had all those bolt-ons, and more, and this worked a miracle for me. The piece has 2 part numbers: F2PE-9F939, and F2PZ-9F939A. I don't have the instructions, but they're with the part, or you can find them over at corner-carvers.com. Be quiet as a mouse over there, 'cause they don't like strangers and they'll flame you in an instant, but they have unbelievable tech. For this info, look at their engine forum.
Oh, yeah. The piece is less than $20!!!

 

[ponycar17]

I think one of the main culprits is the MAF sensor. My 75mm Pro-M caused my car to idle like crap until I got the Pro-M MAF Tuner system. Now, I can adjust the idle voltage of my mass airflow meter, and it stops surging and dying... The problem, in my opinion, is that the MAF voltage is very sensitive for the car to run correctly. If you order a meter from Pro-M or C&L, they don't know your entire setup. They can come close to your exact voltage curve, but they can't get it perfect for your setup. If you're able to adjust the idle voltage, you can compensate for their tune, and effectively make your car idle correctly. This is why you hear some people say that "clocking" their mass airflow meter fixed their idle problems. Effectively, they're changing the idle voltage by changing the point at which the MAF sensor is measuring airflow, and therefore changing the idle voltage of the MAF to the ECU. Well, that's my 2 cents....

 

[IndyBlk5.0]

I just got a failing head gasget, so i dont know if it was this or not, but we messed with vacume lines, adjusted AFPR to 40 psi. and retarded the timing a bit. Seemed to run better but now i have to do a damn head gasket