Major Throttle Problems.

StillAlive · Mar 29, 2006

Alright, so I honestly have no idea what is the deal with my cobra. I have a '94 5.0 s/c (powerdyne) msd btm full ignition system, upgraded MAS, injectors, and fuel pump (40#). New wires, plugs, dist cap, blaster coil, battery, fuel filter. Now this is the situation. I will start my car and it will kind of idle high, but i guess that is expected when it is cold outside, right? And then after a little bit it will calm down to the norm 750-800. But occasionally...when i start my car...it will idle really high to like 1700 and kind of surge up and down...but finally calming down to the norm idle. Then sometimes it will start just fine....but when I am headed down the road my car will try and die on me so I gas it and it is like there is no spark....followed by a quick increase of power...so i take my foot off of the pedal. And it will just surge up and down the RPM range up to 2K (w/o my foot on the gas). I am not too sure what the ordeal is. I have taken the car to Ford and had a "recorder" hooked up to my ECU...and recorded the incident when it happened (maybe a hand full of times a week). And Ford is just clueless...but their recorder only gives outputs such as fuel trims and air ratios. Curious if there is anyone out there that has had some similar trouble when a 94-95 5.0 is S/C'd. I have been living with this situation for a while since I am in the Navy and need that car as a daily driver. It is just annoying as crap to not know what the source is. Does anyone think that it is the chip? Any help would be greatly appreciated.
~Justin~

FORCED2DV8 · Mar 29, 2006

did you change anything recently or when the problem started to occur??
I would check the IAC, make sure it giving the correct voltage. And check the electrical connections for the igntion system. Who did th tuning? what kind of Chip??

StillAlive · Mar 29, 2006

I don't even know what the IAC is. I talked to a shop that said it might be that, but me being the unknowlegeable person on this matter...I am not sure what that is. It would be ridiculous to think that the original shop that did the work up in MD (Altered Atmosphere Motorsports, Inc.) before I bought the car didn't replace the stock chip with a performance chip and tune it accordingly. I got two dyno sheets with the car when I bought it, so the assumption was that the car had been tuned...but I guess not. I honestly didn't replace a single thing on the car before it started acting up. All above newly replaced parts were due to the erroneous outputs of my car. What is the easiest way to check the chip? I'm new at this and would like to start...all positive help is greatly appreciated.

StillAlive · Mar 29, 2006

Okay....so I did my end of research and found out what the IAC is....sounds right. I just don't really understand how the RPM's of the car can increase with no visual change in throttle movement. Just a few minutes ago I went to press up my tires and I couldn't even make it down the street w/o my cobra acting retarded. So, like always, I pull over and pop the hood. The throttle is set and the car is idling around 800RPM...then the car surges to nearly 2K (as heard from the front of my car) and the throttle linkage never moves. I've decided to make haste and drop the car off at a local race shop. Anyone ever had a problem like this before?

crameur · Mar 29, 2006

I have the same problem,i start the car,it Idle normally,after 2-3 min,on stop,Idle Surge to 1500-2000 rpm and down after 1 min,or i can stop the car and restart it,and it's ok ! Today, i changed Iac and two O2 sensor,Idle is better but really hi again !! Tomorow i will check all the gasket,throttle body gasket,intake gasket to be sure of the car dont take air outside.

vristang · Mar 29, 2006

StillAlive said:
Okay....so I did my end of research and found out what the IAC is....sounds right. I just don't really understand how the RPM's of the car can increase with no visual change in throttle movement. Just a few minutes ago I went to press up my tires and I couldn't even make it down the street w/o my cobra acting retarded. So, like always, I pull over and pop the hood. The throttle is set and the car is idling around 800RPM...then the car surges to nearly 2K (as heard from the front of my car) and the throttle linkage never moves. I've decided to make haste and drop the car off at a local race shop. Anyone ever had a problem like this before?

The iac is separate from the throttle plate. The iac is basically a bypass of the throttle body. The computer will open the iac when the idle rpm gets too low (to let in more air/increase rpm), and close the iac when the idle rpm gets too high.

You don't need to take the car to a race shop, just find out if the valve itself is bad (they tend to collect carbon and stick), or if the problem is in the electronics.

At the top of the 5.0 board you will find a sticky called Surging Idle Checklist, or something like that. It should help alot.

BlackVert · Mar 29, 2006

mine often has the searching idle thing when it is cold. just like yours, it will calm down after a couple of minutes, if it doesn't die while searching. or if i drive it right away, it goes away more quickly.

i haven't yet figured it out, but i have heard people say that that kind of behavior can be caused by a too rich condition, and it seems more common with larger injectors (42# and higher).

what size injectors do you have?

mine has never gone gone high like yours on startup, but that might be an indication that the IAC is stuck open. faulty IACs usually have more symptoms than that though, so i doubt it is the IAC.

when it tries dies on you while driving, do you get a cloud of smoke out the back? that has happened to me a few times recently.

final5-0 · Mar 29, 2006

BlackVert said:
mine often has the searching idle thing when it is cold. just like yours, it will calm down after a couple of minutes, if it doesn't die while searching. or if i drive it right away, it goes away more quickly.

i haven't yet figured it out, but i have heard people say that that kind of behavior can be caused by a too rich condition, and it seems more common with larger injectors (42# and higher).

what size injectors do you have?

mine has never gone gone high like yours on startup, but that might be an indication that the IAC is stuck open. faulty IACs usually have more symptoms than that though, so i doubt it is the IAC.

when it tries dies on you while driving, do you get a cloud of smoke out the back? that has happened to me a few times recently.

All you gotta do is dial back a little fuel with the startup table

Grady

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