erratic idle issue on 98gt

[trikeffex]

i have a 98 blown/built/cammed/pi swapped gt and the car runs great,but the only thing is the freaking idle acts up.
on the dyno when i got the car tuned,the tuner couldn't get my idle set,because the tps was giving some crazy numbers on the laptop.
the car will surge 2 or 3 times like its gonna die,and then after that it idles perfect with a lope.then sometimes when you give it some gas and let off,the idle will hang up around 2 grand or so.the tuner thought that the tps sensor might be bad,but i changed it when i got home,and the car is still the same.could it be an egr valve or possibly an iac motor?
i was thinking maybe after i put the new tps sensor on that the tuner could possibly fix the idle but i haven't had a chance to go back up there.any help is appreciated guys.the cams are comp cams xe270's by the way.
charles

 

[Built98GT]

What kind of fuel pump/pressure regulator/and injectors do you have?

 

[trikeffex]

What kind of fuel pump/pressure regulator/and injectors do you have?

standard intake 255lph from dallasmustang,inline 155lph from vortech,42lb ford racing injectors,stock pressure regulator.
charles

 

[Built98GT]

Well it seems as though you have enough fuel upgrades.When my car was being tuned we were having an idle problem and they couldnt get enough fuel pressure until they added the regulator.hope you find out what it is.

 

[TweekedGT]

Sounds like a vacuum leak somewhere. Do you have a Boost/Vacuum gauge or just a boost gauge? If you've got a vac gauge check it to see if it's erratic.

 

[Mike97gt]

what cams do you have? some of the cams can be difficult to tune at idle.

 

[trikeffex]

what cams do you have? some of the cams can be difficult to tune at idle.

they are the comp cams xe270's.
the vacuum looks fine until it starts to surge like its gonna die,then it starts to lose vacuum until the rpms come back up.
but after it surges 2or3 times the car idles perfectly.only aggrevating part is usually when it starts to surge it dies on the 2nd surge,and its always at red lights
charles

 

[reeber]

I had the exact same problem... It's in your MAF slopes on the tune. Do you have aftermarket injectors? Aftermarket MAF? If so, is the MAF calibrated to your injectors? If so, you have to data log your car at idle and give it gas and watch the laptop record the readings as the idle fluctuates. It's all in the tune of the chip. There is nothing wrong with your vaccum, or fuel pressure. Your tuner just has to experiment with different MAF slopes until it idles correctly. Also, change the idle RPMs up and down with those slopes. What is happening is that the computer is trying to correct the IAC motor as it takes away and let's air in for idling. Your computer has to adjust accordingly. Unfortunately, there is no "standard" fix to this. You have to just play with the tune until it's right. Time consuming, but fixable..

Kauffman Motorsports of Dilsburg, PA is the only tuner that I know of in my area that has close to perfected this issue...

 

[DropTopPony]

What is your compression? Did you lower it with your shortblock? These cars are a PITA to tune with high compression and boost. Its usually the idle/low rpm/low boost situations that are difficult to get tuned properly..Also are you still using the stock MAF?

 

[Mike97gt]

I agree with the guys here that are pointing to your tune.

because of the cam specs you do need to have your tune tweaked not just at WOT but also at idle, would not hurt to tweak the whole tune including light throttle accel and such.

I would try to go back to your tuner or try a different tuner.

This is why i want a wideband 02 and the sct pro racer package. So i can tweak my tune on the street. My car don't need this now but when i do come up with the money to build it, I would want the ability to fix the idle and low load driving problems.

 

[trikeffex]

i have ford racing 42lb injectors and an sct 90mm mass air meter.
the motor is 9-5-1 compression ratio.
i am gonna let the tuner try it again when i get back home cuz i'll have my intercooler/power pipe/smaller pulley installed and will need to get it retuned anyways!!
thanks for the help guys!!
charles