Please Help, Experiencing Foxbody Issues

Maivo

New Member
Oct 5, 2021
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I recently purchased a 1990 v8 5.0 GT mustang and the engine fluctuates from about 800rpm-2500rpm when in neutral, high idle. We replaced the o2 sensors, the EGR valve, cleaned the air filter, and replaced the air flow sensor. It now doesn't idle as high, fluctuating from around 750rpm-1500 rpm when in neutral. The engine sounds really bad when in neutral, sounding like its gasping for air. It takes about 5 minutes of turning the key over and over to get it to start, and the first 15 minutes of driving the car jerks forward like its not in the right gear when in all gears, being unable to surpass around 20 mph. After driving for about 15 minutes there is no problem. The guy I bought it from rebuilt the engine, and everything is stock. Can someone please diagnose the issue?
 
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General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
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Do this checklist, jrichker and other members put this together and it works, just follow directions.
 
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KRUISR

5 Year Member
Apr 16, 2015
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Agreed, Surging Idle Checklist is a great place to start.

It should fire up after a couple of revolutions, not 5 minutes. Sounds like dirty IAC and/or TPS setting (both covered in the Checklist).
 

General karthief

wonder how much it would cost to ship you a pair
Mod Dude
Aug 25, 2016
23,702
8,760
203
Possibly the fuel pump
Possibly a vacuum leak
if you do the checklist starting at the top and do each step, not jump around because you 'think' that may be the problem, you may find and fix stuff that would be a problem sooner or later. Read through the list, have a note pad ready and tell us what you find or if you have any questions you can come back here and we will attempt to help.