Car runs great at first, then shuts off!! - Mustang Forum

Jono1998 · 05-04-2014, 04:18 PM

I just replaced the thermostat, IAC, coolant temp sensor, and installed a BBK mass air meter for 24lb injectors/cold air intake...fired her up sounded great...high idle on the cold start then dropped to normal rpm range and idled fine. I shut it down until I was ready to take it out.....So I fire it back up and idle starts to surge rpm level up then down, up then down like its going to choke itself out and I have to feather throttle until it will idle on its own and gets its act together.

I took her for a spin smacked 1st,2nd,3rd no problem then just cruised in 4th/5th about a mile or so into this it shut off on me at a stop light and would not idle. Once I started it back up I had to feather it to keep it alive but it sounds like it was missing/hesitating and started to buck on me like it did not have any power and wanted no parts of the open throttle. I took her back home and stayed in 4th gear keeping my foot out of the throttle with no issues there, then got in the driveway and it idled fine!! (Not the first time this has happened as to why I replaced some parts previously mentioned)

I'm thinking maybe fuel related but also have been hearing about the TFI module could be doing this as well and also resetting computer? I'm 99.9% sure the fuel pump is stock as well. I also have a fuel gauge installed on the rail and it reads normal range but as to when it started acting up I could not tell you what the gauge was reading being under the hood and I'm driving. Any ideas??

'91 GT
AFR 185 72cc heads
Comp Cam
Cobra Intake
MSD ignition system

modo · 05-04-2014, 07:10 PM

Quote:

Originally Posted by Jono1998

installed a BBK mass air meter for 24lb injectors/cold air intake

id start here

FRED-MATIC · 05-05-2014, 06:09 AM

Quote:

Originally Posted by modo

id start here

x2

Jono1998 · 05-19-2014, 08:16 AM

Quote:

Originally Posted by modo

id start here

Bingo! That solved part of it...It runs great now but im still having some issues, It seems once it warms up and I come to a stop, just about every time it will shut off but I start it back up and feather the throttle again until it idles on its own. I'm good until the next stop lol. weird

modo · 05-19-2014, 02:17 PM

iac and ignition timing are what i would look at

get the car at operating temp then shut it off. disconnect the iac harness and start the car. use the set screw on the throttle body to get the car to idle around 750-800 if its a 5 speed, little more if its a aod. shut the car off. hook the iac back up and take it for a test drive. if it still isn't right you might have to clean / replace the iac motor... otherwise a little more base timing should help as long as its not already too aggressive

05-04-2014, 04:18 PM	#1
Jono1998 . Join Date: Sep 2004 Location: Maryland Posts: 1,849	Car runs great at first, then shuts off!! I just replaced the thermostat, IAC, coolant temp sensor, and installed a BBK mass air meter for 24lb injectors/cold air intake...fired her up sounded great...high idle on the cold start then dropped to normal rpm range and idled fine. I shut it down until I was ready to take it out.....So I fire it back up and idle starts to surge rpm level up then down, up then down like its going to choke itself out and I have to feather throttle until it will idle on its own and gets its act together. I took her for a spin smacked 1st,2nd,3rd no problem then just cruised in 4th/5th about a mile or so into this it shut off on me at a stop light and would not idle. Once I started it back up I had to feather it to keep it alive but it sounds like it was missing/hesitating and started to buck on me like it did not have any power and wanted no parts of the open throttle. I took her back home and stayed in 4th gear keeping my foot out of the throttle with no issues there, then got in the driveway and it idled fine!! (Not the first time this has happened as to why I replaced some parts previously mentioned) I'm thinking maybe fuel related but also have been hearing about the TFI module could be doing this as well and also resetting computer? I'm 99.9% sure the fuel pump is stock as well. I also have a fuel gauge installed on the rail and it reads normal range but as to when it started acting up I could not tell you what the gauge was reading being under the hood and I'm driving. Any ideas?? '91 GT AFR 185 72cc heads Comp Cam Cobra Intake MSD ignition system __________________ 2004 Mach 1 Azure Blue 1991 Mustang GT 1988 Mustang GT - SOLD 2002 Mustang GT - SOLD 1998 Mustang V6 (MSC # 015) - SOLD

05-19-2014, 02:17 PM	#5
modo That Guy Join Date: Jan 2002 Location: In a house Posts: 10,248	iac and ignition timing are what i would look at get the car at operating temp then shut it off. disconnect the iac harness and start the car. use the set screw on the throttle body to get the car to idle around 750-800 if its a 5 speed, little more if its a aod. shut the car off. hook the iac back up and take it for a test drive. if it still isn't right you might have to clean / replace the iac motor... otherwise a little more base timing should help as long as its not already too aggressive __________________ 93 GT 66 Coupe