Surging Idle Need Help!!!!

[91StangLX]

Ok here it is, I just replaced the Heads with GT40P with 1.90 x 1.60 valves, TFS Stage 1 camshaft, Professional Products Typhoon Intake, 24lb injectors, 255LPH fuel pump, Adj. fuel regulator (Pressure set to 32PSI with the vacuum line off and jumps to about 37 with the vacuum line on), Autolite 764 plugs gaped at .45, FRPP 9mm plug wires, FRPP cap and rotor, TFI module and 1.6 roller rockers. I am running a 65mm Throttle body and the TPS is set to .98 volts. I am also running a C&L Mass Air Meter with the coreect 24lb sensor. Car runs will strong and has dynoed over 300 HP... The problem I am having is the Idle. Sometimes it is fine and idles at about 950 RPM then I put it gear and drops to,about 750-800 RPM and is fairly smoothy. Then sometimes it will idle at about 1100 RPM will kick up to about 1500 when put in gear. I can actually put it in gear and not touch the gas and it will idle at 1500 rpm and move the car down the road at 25 mph... I am at a loss... When it does idle right it runs smooth as silk and has a lot of power and throttle response. When it is not idleing right it is very sluggish with hesitation in the throttle.

Does anyone have any suggestions for me, this is driving me bannanas...

 

[Luvmy88]

You reset your computer after all of these additions?

 

[b1gp1mp1n247]

i would say that your fuel pressure is way too low. im pretty sure that it should be atleast 40 vacuum off. and like luvmy88 said make sure you reset your computer after all this by taking the negative battery terminal off for 5-10 minutes. also check for vacuum leaks. good luck

 

[eagle87]

Change ect,act if it still does it after that I would look into the vss. And if i where you I would go to fordfuelinjection.com and talk with Ryan he's great with this stuff. good luck

 

[Johnny K]

My car idled funny after a throttle body install. Aftermarket headers also caused my car to surge. It was driving me nuts and then I saw a part offered from steeda that allows you to adjust your idle on your car.

http://www.steeda.com/

click on mustang – fuel and induction – scroll down to idle bypass valve

I found out from steeda that the part is actually a factory ford part. I work at ford so I did a little research on this part. I found that this part was issued for a TSB. The TSB stated that the symptoms were a surging idle. I think the 90's cars came stock with this part where as my 87 did not. I bought the part straight from ford and followed the directions in the kit. Worked great and no more idle problems.

The surging is caused by the Idle air bypass (IAB), after carbon builds on this component it sticks and then makes a drastic change in the idle and once it "frees" itself the car will start to surge where it gets itself into and endless cycle until you rev it up or something. Large cams and aftermarket heads can cause the surge too. If you have a car equipped with the plate then adjust the screws in it to get the idle right, but disconnect the harness from IAB to do this.

I would also check the fuel pressure as suggested above. For some reason 44psi is sticking in my head??

Hope this helps,
John

 

[MatthewP]

Take your IAB valve off and clean it with carb cleaner. With the IAB harness disconnected, set your idle RPM with the throttle plate screw on the throttle body, then set your TPS sensor to about .95 V. The voltage output on many of these sensors increases when they get hot, so I prefer a little less than the much quoted .98V to be sure that you are not over 1V when hot. Reconnect the IAB harness. This procedure works in many cases.

-Matthew

 

[91StangLX]

Take your IAB valve off and clean it with carb cleaner. With the IAB harness disconnected, set your idle RPM with the throttle plate screw on the throttle body, then set your TPS sensor to about .95 V. The voltage output on many of these sensors increases when they get hot, so I prefer a little less than the much quoted .98V to be sure that you are not over 1V when hot. Reconnect the IAB harness. This procedure works in many cases.

-Matthew

Something interesting... If I unplug the IAC it idles smooth as glass... So I purchased yet another new IAC and hooked it up, same problem... Idles fine unplugged and bad when plugged in... This has really got me stumped... I am almost tempted to leave it unplug except for the fact I still have a operating AC unit and need it.

 

[MatthewP]

The problem may lie with your recalibrated MAF sensor. It can throw the load calculation off in the PCM, which can cause the surging problem you are having. I bet if you installed your stock MAF and adjusted your idle fuel pressure (with vacuum hooked up) to about 30 PSI to compensate for the larger injectors, it would idle fine with the IAB hooked up. If it does, consider a chip to smooth it out with the bigger meter.

-Matthew

 

[95stocker]

what you need is an IAC SPACER. You can get them from FRPP.