98 Mustang GT will not idle

[NightlyDaze]

So my car (98 Mustang GT) for the longest time had problems running in general, and especially idling. The guy who did my exhaust cut the cats out for whatever reason without telling me So I've changed the IAC, the plugs, wires, fuel pump, and now injectors. The injectors makes the car RUN like a dream. However, it's been hard to turn over lately? It'll go to start but won't ignite for a little bit. The car misfires quite a bit as well. When I'm sat at a red light or push in the break hard enough, it'll go try and die QUICK unless I rev it. I'm really not sure what else to replace. Some other are saving it could be related to the EVAP, not sure. It does have an exhaust leak in the right header I haven't fixed yet.

I did have to replace the tranny. It was an auto, now has a T45.

Maybe related? My AC always blows hot exhaust smelling air into my cabin. Any idea why?

 

[wmburns]

It does have an exhaust leak in the right header I haven't fixed yet.

This will make the motor run chronically RICH. Even worse this will be only on one side.

The car misfires quite a bit as well.

When working on car driveability issues the first thing to work on is misfires.

However, it's been hard to turn over lately? It'll go to start but won't ignite for a little bit.

Try this. Turn the key on/pause/off several times without cranking. Does this improve starting? If so consider that fuel pressure leak down as a possible cause.

Troubleshoot IAC idle problems 1996-2004
https://www.stangnet.com/mustang-forums/resources/troubleshoot-iac-idle-problems-1996-2004.13/

Howto perform charging system voltage drop test
https://www.stangnet.com/mustang-fo...perform-charging-system-voltage-drop-test.56/

 

[NightlyDaze]

wmburns, you know I've been trying to narrow down that misfire issue but I can't figure it out. I guess I'm going to start trying to fix the exhaust leak on the header but it keeps burning and spitting out the gasket. Like I've gone through two already. Also would the no cats cause my O2 sensors to be wonky or something?

 

[wmburns]

Also would the no cats cause my O2 sensors to be wonky or something?

Let me ask you. Where are the cats located in relationship to the front O2 sensors? If you said after the front O2 sensors then give yourself a pat on the back.

Sooooooooo given that the cars are located AFTER the front O2 sensors then how is it possible for a problem with the cats to "cause" a front O2 sensors (other than clogged cats)?

Advice. Stop looking for some esoteric cause when there's a HUGE reason staring you straight in the face. See Occam's razor.

https://en.wikipedia.org/wiki/Occam's_razor

IF multiple gaskets are burning out it stands to reason there's a REASON.

 

[NightlyDaze]

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[GDawg]

This may be obvious but is your "check engine" light on? Is your car throwing any codes? If so, what are they?

 

[NightlyDaze]

This may be obvious but is your "check engine" light on? Is your car throwing any codes? If so, what are they?

The only things it throws is O2 Sensor Circuit and O2 Sensor Heater Circuit. However, after running it for a couple months, it also said system too lean and Cylinder 4 & 5 misfire detected.

I cleared those codes and drove the car for about a week but the only thing that came back is the O2 sensor codes.

I also just swapped the coil packs and I didn't seem to fix anything.

 

[GDawg]

With limited information and not being able to see the car as a whole, I would be concerned about the exhaust leak in the header. This would most likely cause the upstream O2 sensor to give a false reading. With a false reading the computer is going to set the air/fuel mixture incorrectly hence a possible bad idle. Address that leak before you do anything else with the car and see what happens.