1990 Formula 5.0 TBI. In general, it runs "ok" for a 29 year old car. Main issue is that the motor dies whenever I have to use moderate to heavy braking. i.e., someone pulls out in front of you, light changes to yellow on a street with a decent speed limit. After popping the shifter into neutral, the engine will fire right back up. Any ideas?

 

Could the "moderate to heavy braking" be impacting Vacuum/MAP causing the stall? Like a vac leak in break booster or in the lines to the Vac ball or Intake? Just bouncing ideas until a Sr member chimes in.

 

So basically when the engine is dragged down to idle quickly then it undershoots and dies? Sounds like it could be starved of air.

 

I will check all vacuum lines later this week when I get a chance. Thanks for the tip.

 

The motor/intake is bone stock, air filter has less than 200 miles on it. I will be doing ultimate tbi upgrade later this spring. Hopefully that will increase airflow.

 

I was talking about idle air flow with throttle blade closed. As in throttle blade position, failed IAC valve, vacuum leaks causing idle instability etc...

 

I see what you are saying. I have an extra IAC valve in my spare TBI unit. I'll swap them out and see if it makes a difference.

 

you might try putting a t-fitting in line with the brake booster line, put a vac guage on it, and pump the brakes a bunch. see how vacuum reacts.

 

Probably not anything to do with vacuum.

More likely, fuel starvation.

Fill the tank. NOT, put gas in it; FILL IT. If it clears up you just found your problem.

 

It acts the same whether the tank is full to the filler neck or sitting at a quarter tank.

 

Well that sucks, because the gas tank problem is certainly an easier fix! I thought Sofa was on to something. These cars are known to have fuel starvation problems when tank is low, but I think general consensus around here is that around 89ish all cars received baffles, which fix the issue. however, the baffles do get old and break from what i have heard. still lots of rumors on this issue

 

BTW - you may be able to simulate this problem by just pumping the brakes a bunch while at idle. see if anything happens. easy test.

 

The fuel tank was replaced about 5 years ago. The car sat for about 14 years with about half a tank of gas. It was cheaper to replace than clean.

 

still got that gas tank? i'm looking for one.

 

What he said.... Had it happen, does your tank have the baffles in it?

 

Sorry, it's long gone.