Vintage Mustang Forums banner
1 - 7 of 7 Posts

·
Registered
Joined
·
4,926 Posts
Discussion Starter · #1 ·
I was asked today for suggestions to solve a driveabilty issue on a 1990 GT 5.0. The car can't seem to find its idle. I recall reading about this problem and the reasons was the inabilty of the engine management computer to adjust the tune for significant aftermarket bolt-ons. This car has GT40 heads with a complete Cobra intake package, including mass air meter and throttle body, plus 24lb injectors. I suspect his problem can be solved by replacing the computer with a 1993 non-cobra service replacement computer. Does anyone recall what year of computer offered this problem? Any other suggestions on dealing with this idle problem?

Thanks
 

·
Registered
Joined
·
7,294 Posts
Bad or dirty MAF, sticking/bad idle air control are the first 2 on my list, after not enough air getting by the throttle plate at idle. Could also be that it needs the idle speed adjusted with a chip, but that's usually for cammed cars.
 

·
Registered
Joined
·
2,392 Posts
GT40 iron heads, Cobra intake & MAF, and 24lb injectors is the exact set up used on the '93 Cobra 5.0, the only difference being the Cobra also had a split pattern cam as opposed to the HO cam that had equal int/exh lobes. I would think a Cobra ECM would work well, but a stock HO ECM with MAF should be able handle this mild level of mods also. It's probably something simple like a dirty or malfunctioning sensor. The pre-89 EFI system was speed density and prone to idle hunting with only minor mods, but the MAF systems are more flexible.
 

·
Registered
Joined
·
1,036 Posts

·
Registered
Joined
·
2,483 Posts
I drove a 1990 5.0 for 10 years as a daily driver with very similar mods. The idle would search occasionally, but 80% of the time it was fine. All my buddies also had modified 5.0 Mustangs and not one of us changed a computer. Maybe we just became numb to it. Make sure the sample tube in the MAF is for 24lb injectors. Good luck troubleshooting!
 

·
Registered
Joined
·
4,926 Posts
Discussion Starter · #6 ·
Thanks everyone for the suggestions. I printed all, including the stangnet reference, and will pass them along.
 
1 - 7 of 7 Posts
Top