1989 mustang map question

money_man · 10-17-2009, 10:22 PM

I think i've finally figured out why my car has had a horrible surge issue and hard starts. I was not the one who installed the rebuilt motor but it has a maf sensor and a map sensor hooked up. the previous owner got fed up and traded me the car with this problem. I was going over the car today and pulled the vacuum line off the map sensor and wa la the car stopped surging, the idle dropped to around 700-800 instead of 1400 (he had it set to 2000 when i first got the car)

now with that said, if i put my thumb on the end of the line from the map there is a vacuum but the car starts hunting again. so what am i to do with the vacuum line? leave it off or plug it into something else? the car seems to drive fine in the driveway and no more hesitation at start up so i can't see why leaving it off would be an issue.

I'm sorry if this has been asked before but all i can find is to block off the line or something and i should be good, but if it's this line then the problem starts again.

thanks

Brandon

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mjr46 · 10-17-2009, 10:26 PM

vaccum line must be capped off, the map is a baro sensor on a maf car and no vaccum line should be hooked to it

money_man · 10-18-2009, 12:28 AM

any idea's on what would cause the idle issue if when i have the line sucking air it's fine but when its blocked off the idle screws up and it doesnt want to stay running?

mjr46 · 10-18-2009, 12:32 AM

perform a base idle reset

money_man · 10-18-2009, 01:02 AM

ok im going to try this tomorrow morning.

mjr46 · 10-18-2009, 08:27 AM

look in the tech articles if you need a "how to"

money_man · 10-18-2009, 10:47 PM

got the idle down to about 700 from 1000 but still hunts and eventually dies if i block off the vacuum line. I drove it all day with the line just sucking air, and it worked great. unless it's going to do some form of damage i really see no reason to block it off.

mattdel · 10-18-2009, 11:02 PM

it will cause damage eventually, depending on how you drive it. you're letting unmetered air into the motor, therefore the computer isn't adjusting the fuel and timing curves for that air = lean.

money_man · 10-19-2009, 08:16 PM

ok, i got talking to the guy who owned the car before me. he said he was told to put in 24lb injectors but from everything i've read 19lb injectors are good til 300hp. my car definitely doesnt make that much. just heads and a e303 cam. he never programmed the computer and he never got an aftermarket maf sensor. Do you think going back to 19lb injectors would be a good idea? I have the ones he took out there was nothing wrong with them.

money_man · 10-22-2009, 05:11 PM

well idle issue is back. went out this morning and it won't stay running, it was a cold night with ice on my windows but that doesn't explain why it won't stay running now. also when I put my hand behind the exhaust tip it gets soaked in fuel. could that be a temperature sensor?