Idle Surge Veterans: 2 Questions Please

Bravin Neff · Nov 6, 2010

Hi everyone. I've got a 95 GT with 331 shortblock and Trickflow 170cc Twisted Wedge HCI combo. I have the dreaded idle surging issue. 2 questions please:

1. If the idle surges when the IAC is disconnected, is this a deadgiveaway to look elsewhere?

2. If the idle surging fixes itself - it settles down - after the engine warms up for a minute or two, is this a giveaway that it is NOT a vacuum leak?

Thanks everyone. Great forum!

Regards,
Bravin Neff

BruhBrahBrad · Nov 6, 2010

Also interested in this.

rz5.0 · Nov 6, 2010

could be oxygen sensors. could be running rich. do you get a cel light

95 svt cobra · Nov 6, 2010

90% of people ive encountered with idle problems are people who have mods to their cars. Did you ever get a tune for your car? the 94-95 computers are absolute supremacists when it comes to deviating away from stock.

Bravin Neff · Nov 6, 2010

I don't get the check engine light -- I don't know that this means its not running rich, but I don't get CEL. On the other hand, I am just about to install a wideband O2 sensor, so in the not too distant future I'll be able to say with confidence if I'm running rich or not.

rz5.0 said:
could be oxygen sensors. could be running rich. do you get a cel light

Bravin Neff · Nov 6, 2010

95 svt cobra said:
90% of people ive encountered with idle problems are people who have mods to their cars. Did you ever get a tune for your car? the 94-95 computers are absolute supremacists when it comes to deviating away from stock.

Yes, my car has a Trick Flow top end and full exhaust. The car has been tuned on a dyne with a Superchips chip. But I get the surging regardless if the Superships is installed or if I let it run with the factory tune. So I'm guessing either "tune" isn't addressing the idle portion of the current engine modification state.

I just purchased a Moates Quarterhorse that I should be receiving a couple weeks, plus I'll be installing a wideband O2 sensor. Hopefully this will allow me to fix the surging thing, but I'm currently at a loss understand what is CAUSEing it, hence my original post. Thank you.

Regards,
Bravin Neff

ryclef331 · Nov 6, 2010

A tune will help the issue out. did your tuner just take your car strap it on the rollers and tune for WOT? Tuning for max power and tuning for driveability and power are two different animals. Most tuners will just tune for WOT and show you the horsepower gained and pat themselves on the back. If you're surging before the car is up to operating temp, its ignoring the o2 sensors during warm up. Two things you can check, the amount the throttle boddy is open by adjusting the throttle return stop...IF you mess with this, then you also have to check the second thing. The TPS sensor voltage. I solved most if not all of my surgin issues by drilling an 1/8th hole in the throttle blade on my old 331. people will disagree I'm sure saying its a band aid fix....hardly. New heads, cam, intake, bigger motor, etc. That car NEEDS more air to idle steadily. The factory IAC can't keep up with the increased air flow so it over compensates by opening too far and closes too far hence the surge. A tuner that knows what he is doing can adjust those parameters. I've also had success on other cars with blocking off the IAC Valve alltogether and drilling the throttle body. The car ran like a choked carb'd car until it got to operating temp so this option may not be for you. It was more of a hardcore street stip machine. If you are looking to just jump in it and go daily, a tune may be the best option for you.

gregbar · Nov 6, 2010

I had that issue but it is gone. My combo is 349, 185AFRs, 1.7 scorpion rockers, Long tube headers, MAC pro chamber, 2 1/2 inch cat back. The first time I built the motor it ran like crap, this was without a tune. I now have a Moates Qaurter Horse and have been tuning. WHAT A DIFFERENCE!!!!!!!! I cannot stress the effect tune has. I started by tuning for driviablity first and as a matter of fact I have not done a WOT yet. There is also a HEGO delay that can have an affect on surging. Be careful with the throttle stop. The computer uses that voltage to determine if you are at idle. If you start opening it up it affects that. Mine was open too far. I have closed mine to produce 0.97 volts at idle. You want the IAC to be at 50% that way it can recover in either direction.

Bravin Neff · Nov 6, 2010

gregbar said:
I had that issue but it is gone. My combo is 349, 185AFRs, 1.7 scorpion rockers, Long tube headers, MAC pro chamber, 2 1/2 inch cat back. The first time I built the motor it ran like crap, this was without a tune. I now have a Moates Qaurter Horse and have been tuning. WHAT A DIFFERENCE!!!!!!!! I cannot stress the effect tune has. I started by tuning for driviablity first and as a matter of fact I have not done a WOT yet. There is also a HEGO delay that can have an affect on surging. Be careful with the throttle stop. The computer uses that voltage to determine if you are at idle. If you start opening it up it affects that. Mine was open too far. I have closed mine to produce 0.97 volts at idle. You want the IAC to be at 50% that way it can recover in either direction.

Thanks for the reply. I will try adjusting the throttle stop to produce 0.97 volts. Are you using Binary Editor? I have downloaded and have been playing with it in preparation for receiving the Quarterhorse. Wow, it's pretty intimidating. I've downloaded my QBAZA strategy and 4TM0 bin files. Any advice on what to do? Thanks!

Bravin Neff · Nov 6, 2010

ryclef331 said:
A tune will help the issue out. did your tuner just take your car strap it on the rollers and tune for WOT? Tuning for max power and tuning for driveability and power are two different animals. Most tuners will just tune for WOT and show you the horsepower gained and pat themselves on the back...

Thank you for the suggestions. My car was tuned at a dyno shop (Livernois Motorsports) before I owned it. The tuner burnt a Superchips chip for it, but whether i run the Superchips or not, the surging is the same.

toyman · Nov 6, 2010

Bravin Neff said:
ryclef331 said:

A tune will help the issue out. did your tuner just take your car strap it on the rollers and tune for WOT? Tuning for max power and tuning for driveability and power are two different animals. Most tuners will just tune for WOT and show you the horsepower gained and pat themselves on the back...

Click to expand...

Thank you for the suggestions. My car was tuned at a dyno shop (Livernois Motorsports) before I owned it. The tuner burnt a Superchips chip for it, but whether i run the Superchips or not, the surging is the same.

You may have missed the point. If the tuner was focusing on WOT and not drive-ability the tune would NOT address the idle surge issue. That may be why the surge is there with or without the chip.

Bravin Neff · Nov 6, 2010

You may have missed the point. If the tuner was focusing on WOT and not drive-ability the tune would NOT address the idle surge issue. That may be why the surge is there with or without the chip.

No, I got that, but thank you. In fact I am pretty sure the chip did essentially nothing related to my idle.

gregbar · Nov 7, 2010

Yes Imanother running Binary Editor and also EEC Analyzer. Just another idle thing. The TPS voltage needs to be between 0.95 and 0.99 volts. What I watch is the voltage AND the ISC DC (idle air motor duty cycle). I try to get 50% ISC DC. My current tune 0.97 and 44.92%. The car idles rock solid STEADY unlike previous. What to do first. Get familiar with BE, look at all the PIDs, find, update, save etc. When you get your Moates Quarter Horse there is a few tricks I can help you with.

Bravin Neff · Nov 8, 2010

gregbar said:
Yes Imanother running Binary Editor and also EEC Analyzer. Just another idle thing. The TPS voltage needs to be between 0.95 and 0.99 volts. What I watch is the voltage AND the ISC DC (idle air motor duty cycle). I try to get 50% ISC DC. My current tune 0.97 and 44.92%. The car idles rock solid STEADY unlike previous. What to do first. Get familiar with BE, look at all the PIDs, find, update, save etc. When you get your Moates Quarter Horse there is a few tricks I can help you with.

Thank you for the tips! I will PM you when I get the QH.

2002BLGT · Nov 11, 2010

the MAF and injector combo can greatly reflect how much changing has to be done to the tune as well , what are you running for both ?

Bravin Neff · Nov 11, 2010

2002BLGT said:
the MAF and injector combo can greatly reflect how much changing has to be done to the tune as well , what are you running for both ?

I've got a Granatelli 75mm MAF calibrated for 36lb injectors, plus Accel 39 injectors. I am still trying to understand what kind of statement "calibrated for 36lb injectors" really means to the person that has full control of the actual tune of the car.

95-stang · Nov 12, 2010

A good question, if my pro-m maf is calibrated for the 24lb injectors, why do you need the Maf curve for the Quarterhorse.

2002BLGT · Nov 17, 2010

Cause the proper way to tune the car is the load the proper injector values into the tune , and then enter the correct MAF transfer function , so that the vehicle sees the proper air/flow and load , everything the computer does is calculating air/flow so with a calibrated meter and injectors without tuning is just a hack job way of getting the car to run and it will never run as good as it would if you enter all the correct info into the tune.