when i start my car it start off at 1500 then it dies down to around 700 - 800 like its suppose then after a minute or after driven for a couple minutes i go to a stop then it goes down to like 200 and up to 1100 then down to 600 and up to 900 it goes crazy, and its not my IAC cause i changed that last week, also when im driven around 20 - 35 mph and i put my foot lightly on the gas my car bucks so bad it feels like my car is going back and forth only when im going that speed and when i put my foot slightly on the gas, i dont no what it is, im thinking soark plugs, coils, wires, maybe fuel injectors?

 

Load your stock program back on your ECU (From the Diablo) and drive it around to see if it still does it. Then reload the Daiblo tune. The only other thing I can think of is a vacuum leak, spray some WD40 around your vacuum hoses and see if it changes the idle, if so, then it's a leak

 

Try disconnecting your battery for 15 min and after you connect, start up the car and let it idle w/o anything on and then let it idle w/ your AC on. Then, go for a test drive doing a lot of low rpm driving. Your idle trim curve may need to be relearned. Also, when checking for a vacuum leak, don't you usually use carb cleaner?

 

ill have to try that when i get home, thanks for the help

 

Ok, load your stock progam into your car. Start it and drive for a little bit. Then turn you car off and turn your headlights on. Pop the hood and unplug your battery. (This erases any memory on your ECU) Let it sit for about 10 mins. Leave the headlights on! Plug your battery back in. Turn your headlights off and reload your Diablo Tune. Start it and drive it for a little while. (it might take a day or two) Your ecu will write a new plan for running your engine. This will help the idle.

 

I've always done WD40 but it makes sense, since it could feasibly make it's way into the combustion chamber that it be carb cleaner or starting fluid.

 

WD-40 eats away at hoses.....use carb cleaner

 

Check around your EGR tube. Its on the back of the throttle body. Try to listen for a leak there, you can also check by sticking your finger under it were it connects to it to see if it is sucking in any air. My friends car had a crazy idle just like you explained and that was his problem.

 

ok i loaded my stock tune back, waited a little bit and did everything and it still did it im guna try using the carb cleaner and check my egr tube tommorw

 

sounds like either a IAC problem or could also be a O2 sensor problem, now I saw that you replaced the IAC but did you use and OEM one or some parts store replacement, it does make a difference.

 

Anything hissing underneath the hood.

Im thinking possible Vaccuum leak. When is the last time you replaced your PCV valve? Use carb cleaner and spray it over the engine bay. Listen for the idle change (it should speed up if im not mistaken). That should help you isolate where exactly your problem is.

Most of the time with vac leaks on these cars its not due to the hoses cracking (which I have done on my own, dont ask), but its due to the barbs that connect the hoses together cracking, producing a small leak. Even a leak that is incredibly small can still do this. I know. Its done it to mine before!

 

used an oem iac bout 2 months ago, and i never changed the pcv ethier, ill try the and see if theres a vacuum leak and if that dont work ill try replacing my pcv

 

you no wat randy now that i tihnk about it my check engine light came on a month ago i forget the code but it was something about my o2 sensors

 

They might not be heating up to temperature.

Replace the PCV with a Motorcraft PCV (trust me on this), check for vaccuum leaks, and THEN, after all that, check the O2 sensors. Easiest way to do that is to switch the O2 sensors from one side to the other (Obviously disconnect them and switch them, dont just switch the harnesses between them). If one throws a code, go under the car, switch them back. See if the code comes up on the other side. If its an O2, thats where its going to display itself.

The other way to test is to see how the car performs if you put it into open loop (WOT). If it seems to perform fine in open loop, it could very well be a O2 sensor.

The other thing I can think of is possibly bad gas. When is the last time you changed your fuel filter? If you cant remember its probably due.

Here is your process of elimination:

REPLACE PCV VALVE FIRST!! (Cheapest thing to do)
Check for vaccuum leaks by using carb cleaner
Switch O2's from one side of the midpipe to the other (you only need to switch the front two, dont worry about the rear two) and check for any CEL's going off
Put car into WOT and see what happens (keep stock tune on there!)
Then I would look into possible issues w/ your fuel system.

 

well, there's a start. how many miles on them?

 

Psst...I posted first...and my post is better :P and gives a better logical deduction of problems.

 

 

shambles, i replaced the pcv valve and checked for vacuum leaks witht eh carb cleaner, everythin was good, i then switched the o2 sensors! then 2 codes come on, p0430 and p1131, 0430 is o2 sensor not working right and 1131 means im runnin lean i think i duno i googled it and thats what came up. what should i do now? i think i might have to change my o2 sensors, and randy my car has about 95k miles on it

 

which O2 is 0430...

Give randy a post in his parts section. Just replace that O2 and that will be a step in the right direction.

 

passenger side o2 sensor

 

Theres what you need to replace!

 

goin to auto zone after work to pick 1 up there like 60-70 bucks and about 1 or 2hr labor shouldnt be bad at all ill knock it out in 2 hrs

 

thanks for the help!

 

Nooooo, Don't do-it get genuine Ford!! parts store electronic stuff does not work well on Fords and Ford O2's are only $69.00 each + shipping and we have plenty.

Do Not Buy Sensitive Electronic Parts for Fords at parts stores!!

Ford designs a part to work wthin certian parameters, say A to D and the aftermarket opens up these parameters, say from A to G to work on other brands of cars, thats why ther parts are cheaper(sometimes) then OEM stuff.

 

I ditto what Randy said, especially with o2 sensors. They are a critical component to how the car operates.

My initial thought was a dirty MAF but have not heard anyone chime in on this yet.

BUT sounds more like an O2. Another thing you mentioned is that the problem does not ocurr during cold start right? When you first start the car, you are in open-loop, right? This means that the O2's are not involved right away in the tune.

 

Until they heat up I believe the car goes off of whatever is programmed to the ECU. Once they are at temp it switches to closed loop.

 

i thought it was the MAF but i cleaned that out with carb cleaner, good thing ya's said something cause i woulda gottin 1 from auto zone, im gona hit up the ford dealership down from my house and get 1, thanks again for savin my ***

 

good deal, now if they dont have them or are way-outta' line wth the price, give me a call

 

My car (98GT) was doing the exact same thing, the horible idleing, kept missing, very bad bucking, even stalled at stop signs, my check engine light came on, did a scaner on it, said runing lean, and o2 sensors, so I replaced my o2 sensors, still didnt do anything, so my friend told me sounded like a electrical problem, so I changed my plugs, wires and coil packs, and now my car runs perfect! no more bucking, smooth idle, try changing plugs and wires first, if that doesnt do it then I recommend the coil packs good luck

 

been awhile since i posted but the other day i got my o2's changed and i also changed the ignition coils and wires (msd) and spark plugs (ngk) and the car runs great! the buckin stoped which is awsome, thanks for the help guys!