Cold idle surge, gone when @ operating temp
08-15-2009, 11:24 PM
#1
Thread Starter
Join Date: Aug 2009
Location: Washington
Posts: 5
Cold idle surge, gone when @ operating temp
Hi,
I am a new member and a new mustang owner. I have a 1990 Mustang GT 5.0 manual trans with 136xxx miles. mods are : computer chip, short throw shifter, 160 thermostat, electric fan, full length headers, straight pipes, no cats, 70mm throttle body and egr spacer, summit racing CDI ignition, believe it has a larger MAF but not positive, k&n cone filter, under drive pullies, no smog pump. Problem is when cold start my idle surges to about 1400 down to damn near 300 and will stall if i dont feather the throttle, and when i start to drive it will "pop" through the intake if i try to accelerate hard, problem is not there when its warm. Here is what i have done so far: searched forums, changed plugs, wires, cap, rotor, fuel filter, spread terminals on "salt and pepper" connectors, cleaned IAC, cleaned MAF, adjusted TPS voltage, set timing to 12*, set base idle to 750, cleaned egr valve and passages, could not find vac leaks, replaced ECT sensor, coolant is full. no codes, am pulling my hair out trying to figure this out, please help!! thanks alot in advance!!
I am a new member and a new mustang owner. I have a 1990 Mustang GT 5.0 manual trans with 136xxx miles. mods are : computer chip, short throw shifter, 160 thermostat, electric fan, full length headers, straight pipes, no cats, 70mm throttle body and egr spacer, summit racing CDI ignition, believe it has a larger MAF but not positive, k&n cone filter, under drive pullies, no smog pump. Problem is when cold start my idle surges to about 1400 down to damn near 300 and will stall if i dont feather the throttle, and when i start to drive it will "pop" through the intake if i try to accelerate hard, problem is not there when its warm. Here is what i have done so far: searched forums, changed plugs, wires, cap, rotor, fuel filter, spread terminals on "salt and pepper" connectors, cleaned IAC, cleaned MAF, adjusted TPS voltage, set timing to 12*, set base idle to 750, cleaned egr valve and passages, could not find vac leaks, replaced ECT sensor, coolant is full. no codes, am pulling my hair out trying to figure this out, please help!! thanks alot in advance!!
08-15-2009, 11:31 PM
#2
4th Gear Member
Join Date: Aug 2007
Location: Texas
Posts: 1,788
Chances are, it could be the aftermarket MAF. Many times these companies cannot accurately calibrate their MAFs to the stock calibration. Don't know why. This can cause all sorts of issues. If you have the stock one, try swapping it out and see if that does anything.
08-16-2009, 01:15 AM
#4
6th Gear Member
Join Date: Nov 2006
Location: Spfld, MA
Posts: 9,240
IAC is the main culprit here. Cleaning it doesn't always work.
2 tips for ya.
#1 Scrap that 160 thermo and get a 185. Not allowing a computer controlled engine to reach its programmed operating temperature is bad for performance & gas milage.
#2 Yank that chip out. Any kind of chip that comes in a box in the mail is worthless and is probably harming your performance. Get a professional dyno tune/custom chip when you have enough mods to warrant such an expense.
2 tips for ya.
#1 Scrap that 160 thermo and get a 185. Not allowing a computer controlled engine to reach its programmed operating temperature is bad for performance & gas milage.
#2 Yank that chip out. Any kind of chip that comes in a box in the mail is worthless and is probably harming your performance. Get a professional dyno tune/custom chip when you have enough mods to warrant such an expense.
08-16-2009, 07:48 AM
#5
5th Gear Member
Join Date: Jan 2006
Location: Puerto Rico
Posts: 3,926
Hi,
I am a new member and a new mustang owner. I have a 1990 Mustang GT 5.0 manual trans with 136xxx miles. mods are : computer chip, short throw shifter, 160 thermostat, electric fan, full length headers, straight pipes, no cats, 70mm throttle body and egr spacer, summit racing CDI ignition, believe it has a larger MAF but not positive, k&n cone filter, under drive pullies, no smog pump. Problem is when cold start my idle surges to about 1400 down to damn near 300 and will stall if i dont feather the throttle, and when i start to drive it will "pop" through the intake if i try to accelerate hard, problem is not there when its warm. Here is what i have done so far: searched forums, changed plugs, wires, cap, rotor, fuel filter, spread terminals on "salt and pepper" connectors, cleaned IAC, cleaned MAF, adjusted TPS voltage, set timing to 12*, set base idle to 750, cleaned egr valve and passages, could not find vac leaks, replaced ECT sensor, coolant is full. no codes, am pulling my hair out trying to figure this out, please help!! thanks alot in advance!!
I am a new member and a new mustang owner. I have a 1990 Mustang GT 5.0 manual trans with 136xxx miles. mods are : computer chip, short throw shifter, 160 thermostat, electric fan, full length headers, straight pipes, no cats, 70mm throttle body and egr spacer, summit racing CDI ignition, believe it has a larger MAF but not positive, k&n cone filter, under drive pullies, no smog pump. Problem is when cold start my idle surges to about 1400 down to damn near 300 and will stall if i dont feather the throttle, and when i start to drive it will "pop" through the intake if i try to accelerate hard, problem is not there when its warm. Here is what i have done so far: searched forums, changed plugs, wires, cap, rotor, fuel filter, spread terminals on "salt and pepper" connectors, cleaned IAC, cleaned MAF, adjusted TPS voltage, set timing to 12*, set base idle to 750, cleaned egr valve and passages, could not find vac leaks, replaced ECT sensor, coolant is full. no codes, am pulling my hair out trying to figure this out, please help!! thanks alot in advance!!
08-17-2009, 01:37 PM
#8
4th Gear Member
Join Date: May 2005
Location:
Posts: 1,267
That and a WB 
Surging at idle is due to the engine running rich. For $200 I will never run a car without one again. I bet you put a WB in and your A/F will be bouncing from about 12.5 when stalling, to about 16 when it picks back up. I can almost guarantee it's due to your chip.
Surging at idle is due to the engine running rich. For $200 I will never run a car without one again. I bet you put a WB in and your A/F will be bouncing from about 12.5 when stalling, to about 16 when it picks back up. I can almost guarantee it's due to your chip.
08-29-2009, 10:07 PM
#9
Thread Starter
Join Date: Aug 2009
Location: Washington
Posts: 5
ill take the chip out and see what happens, set timing back to 10*, and placed a restrictor in front of the throttle body and it seems to idle much better, real test will be tomorrow when i due a true cold start, thanks for the input. im going to leave the chip in for this just to see if the restricion fixes it, but shouldnt the ECM have the abbilitys to monitor the increased air flow over the maf, therefore increasing fuel to keep the AF within the ECM's wanted parameters? thanks for all the input
08-29-2009, 10:26 PM
#10
Thread Starter
Join Date: Aug 2009
Location: Washington
Posts: 5
ok, i heres what my dad found, he performed a compression test, all cylinders are 148-152 psi, set timing back to 10*, plugs are a little light colored (white), made sure the rotor turns as soon as you move the crankshaft, set plug gap to .035, placed a restriction in the intake and it seems to run alot better, true test will be in the morning when it is really a cold start, i am going to take the chip out but i want to see if the larger throttle body is the problem. but wouldnt the ECM have the ability to see the increased air volume moving over the maf and then increase the duty cycle of the injectors to increase fuel to keep the AF within its wanted parameters? but again iether way takin the chip out
