Idle problem when warm

[Georgia50]

Ok boys here is the problem, when I start the car it idles fine, but when it gets up to operating temperature it surges ones or twice and then cuts off, which is becoming a big pain every time I stop at a stop sign or light. Driving down the road it does great pulls, strong as hell, and you can’t tell anything is wrong, but if let off the gas and the RPM’s fall to quick it dies. You can keep it running, but you have to keep it revd up at about 1200 RPM’s. So, any ideas? All help and input will be appreciated.

Hear is what I have done. Cleaned the AIT,MAF, checked the plugs, checked for vacuum leaks.

Hear is my setup.
30lb injectors
Pro-m mas air
Adjustable fuel pressure regulator
2x gt28rs turbo’s
2x 50mm BOV
12x4x36 intercooler
Flow master 40’s
Motor stock
AODE to T5 conversion
453 rwhp @ 10lb of boost
504 ft lb of torque 1994 mustang

 

[Georgia50]

I forgot to mention all the codes

Car running
136- HEGO shows system always lean (left)
172- No HEGO switching detected, indicates lean (right)
The Same codes come up if O2 sensors are hooked up or not.


Key on car off
113- IAT sensor circuit open, or reads -40f
124- TP sensor voltage higher than expected, but with specified range
334- EGR closed voltage higher than expected
556- Fuel pump primary circuit failure

 

[95gtdude]

I used to have a problem almost like that, it would run fine til it got up to temp then the Idle would surge between 500 and 1000RMP and sometimes stall out but runs fine while driving. and I found that during upgrades (heads and intake) that a vaccum "T" connecting my PCV valve hose to my Upper Intake was SNAPPED. I know you said you checked for vaccum leaks but I'd thought I'd share what my fix was or would have been if I hadn't upgraded.

 

[Georgia50]

Can a vacuum leak wait till the car is warm to start messing it?

 

[HISSIN50]

When you let off the gas, does the idle fall quickly or does it hang? Is it the same while rolling or if you just rev it with the car totally stationary?

 

[mo_dingo]

You have a lot of codes stored in your computer. I would remove the ground from the batt, depress the brake pedal, and reconnect the ground. That resets the comp. Then drive it for 20 minutes and then run the codes again. You may find that very few are left.

Because you have good accel at WOT, and when the car is cold, I would say you have a problem with your O2 sensors, your ignition module or the pip module on the bottom of the dizzy. The ig. modules and pip are both susceptible to heat problems. The O2 sensors only work after about ~2 minutes of the car running, and they are the main a/f ratio control.

But the first thing I would do is a cylinder balance test to make sure all cylinders are firing equally. If it passes, then you know your spark/fuel/compression is ok. Then move onto what I said above.
Scott

 

[donjohn]

test your 02 sensors. The manual tells me that there's supposed to be a certain ohmage across the sensor. I got that reading when testing the two white wires. I think it's like 6ohms. I bought a new 02 sensor and am installing it tomorrow.

btw, I have the same problem as you, but not as drastic.

 

[Georgia50]

HISSIN50
The idle falls flat on its face. Yes it’s the same after it warm rolling or stationary.Sorry it takes so long to respond but work at night

 

[mo_dingo]

Have you run a cylinder balance test yet? Have you checked for codes yet?

 

[HISSIN50]

I know you've done it but it still kind of sounds like a vac leak if nothing else has changed. Do you know if you set your idle to require the IAC to keep the car idling when the motor is hot? If not, it could simply be an IAC issue. However, if it idles well when cold or if the AC is on (if applicable), that would suggest the IAC is ok.

 

[WhiteCobra95]

It could be an electrical gremlin, and some of those codes are pretty important. Clearing the DTCs and seeing what comes back is a good idea. If they come back, take a look at your harness. Escpecially with turbos, you might find a burned section of the harness which is shorting somewhere.

 

[95CobraMike]

i had warm engine starting and running issues with my old 95 cobra, when it was a hot day out or if my car would get up to normal temp, it would stall out or not start/restart till it cooled off....

turned out to be the little sensor inside of my distributor... i forget the name of the sensor, but does that sound like what is going on? or does it restart right away?

 

[Georgia50]

Replaced the IAC, cleaned the throttle body set the TPS and the idle. Idles good now at 650 RPM. Thanks for all the help

Chris

 

[WhiteCobra95]

I'm glad to hear it worked out.

Now go smoke some GM's!!!!