car dies when my foot isnt on the gas

[thenasty6]

my 87 grand national drives fine. but if i take my foot of the gas too quickly it will shut off. it always start right up, but dies if i pull my foot off.
i did notice that if i lift my foot slowly the it will idle calmly but it has to be slow and let the motor idle down slowly. and guesses on what it could be. its really annoying to drive with a foot on the gas and the other on the brake.
thanks in advance.

 

[GBGN1]

Sounds like vacuum leak somewhere or get a scan master on it and see what your IAC is set at.

 

[thenasty6]

i was told not to put a scan on it cause it has a fast system on it. but i will go look for a vaccum leake.
also do u think it could b the tps?

 

[Franks86gn]

That's what I was thinking. Not sure if the FAST system is like the factory ECM but, check for .4 - .46 volts at idle.

 

[Chuck Leeper]

So, hook up the laptop, and see what's going on w/ a data log on the FAST........

 

[kidglok]

throttle follower probably needs attention,

like chuck says, hook it up to a laptop

 

[Turbo38V6]

Be curious what happens on this one. My car is having a similar problem.

 

[thenasty6]

So, hook up the laptop, and see what's going on w/ a data log on the FAST........

gonna do it as soon as i get off work.

 

[pacecarta]

check that the throttle blade (iac) screw hasnt backed out as it often does on aftermarket throttle bodies

 

[Blazer406]

It could be several things, but the throttle follower adjustment would be a good starting point if when you hook up the laptop nothing else jumps out.... these guys are steering you correctly......

 

[thenasty6]

ok i got the fast system going, can someone tell me what to look for that could help me out...

 

[pacecarta]

tps

 

[thenasty6]

tps

idling the tps is at 4%

 

[pacecarta]

sounds like the iac screw rolled back

look at idle function> idle parameters...> , min idle setting value
adjust tps using iac screw until its the same or 1 less

 

[thenasty6]

so just go ahead and screw it back in or can i adjust it from the system. sorry still new to set up.

 

[pacecarta]

cant fix a closed door with programming

 

[thenasty6]

ok gotcha. screw it in until it improves. whats a good percentage for the iac to be at or is it just what my motor idles better at.

 

[pacecarta]

if the tune was set correctly it would be similar to a stock car, 10-20 on iac warmed up to operating temp in park
but you really need to be concerened tht the tps doesnt exceed the tps min value set in the idle parameter, typical is 9-13 for tps reading but you need to check your program as there is flexibility depending on whoever set it up

 

[Chuck Leeper]

Post the tune and data log.....

 

[thenasty6]

Post the tune and data log.....

will do when i get off work. i was going to post them anyways just forgot to send them over off my laptop.