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Discussion Starter · #1 · (Edited)
I hope someone can help. I am a member here and am enjoying my new GT. I have a friend that has an 86' 5.0 that I've adored through the years and was one of the big reasons I have my new one now. Last year he started having problems with his car and has tried everything. He's never posted to a forum before so I offered to do it for him, telling him you guys are GREAT and can figure out anything! :worship

Please help if you can. Post suggestions and I'll them right to him.

Here is the text file he sent me about his problem.

Thanks everyone!


"1986 Ford Mustang GT 5.0 (5-speed manual transmission)
•original owner
•believed to be 1990 motor (though a motor serial number check failed to establish this) (original motor replaced after 200,000 miles)
•began reving high on start-up then would level out after warming up
•several months later began reving low/stalling at traffic lights/low RPM
[low idle-stalls on decel or quick stop]
•currently can't exceed 15mph/runs very rough (about 6-7 months ago)
•hard start-ups when cold, then runs better, then runs worse as Mustang computer cycles through it's phases
•EGR replaced
•EVP replaced
•Idle Air Control inspected and cleaned:10/23/04
•Throttle Position Sensor adjusted: 10/23/04 (tracing vacuum leak)
•clean idle bypass valve-
thoroughly clean the idle bypass valve with carb/choke cleaner (10/23/04)
•(recent: 10/11/04) tune-up did not resolve
*cap/rotor replacement: 10/14/04
*replace spark plug wires: 10/14/04
*time motor-ok: 10/23/04
*air filter replaced (9/26/04)
•diagnostic tester identified the following error codes (10-23-04): 4, 12 , 41, 91, 32, 13 (10-2-04?)
---other notes---
•vehicle had passed most recent smog test
•computer chip for automatic transmission "

3,268 Posts
41 and 91 are lean codes for each side of the motor. 12 and 13 are idle speed codes.(Low and high.) The 32 is an EGR problem, the EGR valve may not be seating properly.
Make sure that the MAP sensor holds vacuum, and that the supply hose doesn't have any leaks - they'll make a Speed Density car run poorly.
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