Hello I just bought this 1989 Mustang Gt 5.0. it was running really rough when I bought it. did a lot of work to it runs a lot better, but still surges when idling and it smells like its running rich at idle. it also wont idle at all when cold. (no fast idle either) I did a full tuneup with new ignition wires, plugs, cap and rotor, also replaced all of the O-rings and caps on two of the injectors. I bought a computer scanner to scan for codes tried several times to get codes from the computer, but I get nothing just 3 0s and no check Engine light. I also replaced the EGR valve and IAC valve and cleaned the Mass air meter 3 times with electronic cleaner and proformed a intake clean with throttle cleaner. like I said earlier the car is running a lot better then when I bought it but it surges and no idle when cold. one other important find I found one of the wires that is part of the fusible links had a 3 inch section where bare wire was exposed and probably grounding to the body right in from of the ignition coil. could this of caused damage to the computer? or even burned the computer up and that's the reason for the problems? also replaced all the vacuum lines and fuel filter, and fuel regulator. thanks for your help

 

i dont know about all the technical stuff about the computer or anything but my car was doing the exact same thing on a cold idle. it was surging and wouldnt hardly idle and i put new 02 sensors in it and it fixed it. they were really old and i figured it was worth a try. it runs much better now. i also had a small vacuum leak but you said you replaced all those already. hope this helps

 

now why can't I get any codes to show up with my scanner? is there something I'm doing wrong?

 

to be honest bud i dont really know. i talked to a buddy of mine with several fox bodies and he asked about the o2 sensors. i told him they looked like they were 100 years old and he said give it a shot. if that didnt fix it i could bring them back..(he works at advance auto) lol. i wasnt expecting anything to happen and when i put them in and unhooked the battery for a little while and started it i instantly noticed a difference. smooth idle and i didnt smell gas out the exhaust like running rich anymore. since then its a different car. im not saying it will fix your car or anything because they are expensive. im just saying what it did for mine. i hope this helps man

 

try the Throttle Positioning sensor... mine was bad, and I had surging through all RPMS, loss of power, stalling ,the works...

also, try the o2s... try cleaning them, clean all connections, or replace them and clean all the connections on the harnesses...

 

i have an 89 gt as well and i have a idle problem as well. at cold start, she runs fine with the check engine light ON. when she gets warm, the check engine light goes off and she runs at 2000 rpm for about 5 seconds in every gear then she goes back to regular idle. i already replaced the egr valve, the egr position sensor, the IAC, and the Throttle positioning sensor. WHAT THE HELL????