99 Cobra Runs Rough and Hesitates at Light Throttle

[CudaCobraSVT]

This is only my second post ever, but I hope someone can help because I am at my wits end. I have a 99 Cobra with 240k and a few bolt on mods (MAC CAI, Borla Catback, Steeda Underdrive Pullies, John Lund Tune). Used to run really smooth. Now after I had my clutch replaced (thought maybe the disconnected something) it runs rough and hesitates at light throttle, but runs great if I run her. Also seem to be worse at lower altitudes. I live at 7400 ft. and drive to work a 5400 ft. and it gets worse. I have tested for a Vacuum leak and replaced some of my hoses. Sprayed everything with Throttle body cleaner. I've also replaced bunch of things ...

• Accufab Throttle Body
• PCV
• Spark Plugs
• IAC
• MAF
• TPS
• Gas Cap
• Vac Hose at Oil Separator and to Vapor Canister Purge Valve
• Vapor Cannister Purge Valve
• Oil Dip Stick
• EGR Pressure Feedback (DPFE) Hose / Pipe
• EGR Pressure Feedback (DPFE) Sensor
• EGR Valve
• EGR Valve Control Solenoid / Motor
• O2 sensors

Appreciate any advice.
Thanks,
Joe

 

[98 svt]

How long has that MAC CAI been on there? That's not helping things.
Are you sure the MAF is plugged in?

 

[01yellercobra]

Have you datalogged it? Any codes?

 

[shurur]

No codes?
Check the rubber vac line on the passenger side around the ac dryer/accumulator/catch can.

It tends to be the one that rots out and cracks.
Also all those damn plastic/cohline vac lines.

 

[CudaCobraSVT]

How long has that MAC CAI been on there? That's not helping things.
Are you sure the MAF is plugged in?

The Mac has been on the car since 2008 and about 75K. The MAF is plugged in.

 

[CudaCobraSVT]

Have you datalogged it? Any codes?

No Codes. I have a cheap scanner that hooks up to DashCommand software on my iPad. I need to see if it will actually log data. Fuel Trims are way out of wack when it is running bad, like +25 and I can smell fuel. So it seems to be running really rich.

 

[CudaCobraSVT]

No codes?
Check the rubber vac line on the passenger side around the ac dryer/accumulator/catch can.

It tends to be the one that rots out and cracks.
Also all those damn plastic/cohline vac lines.

I don't think I have found that one. I will check it. Thx!

 

[01yellercobra]

Did you check the FRPS? Is it something that happens constantly or does it come and go?

 

[CudaCobraSVT]

Did you check the FRPS? Is it something that happens constantly or does it come and go?

I don't know how to check it and I have not replaced it. I did see a pending code on my scanner say high fuel pressure, but it never actually was issued to cause the engine light turn on.

 

[01yellercobra]

I don't know how to check it and I have not replaced it. I did see a pending code on my scanner say high fuel pressure, but it never actually was issued to cause the engine light turn on.

Normally you pull the vacuum line and if there's gas or it smells like gas the FRPS is bad. It could be on the way out if there's a pending code that hasn't set yet. I had one blow so bad that when I removed it I was able to blow through it.

 

[CudaCobraSVT]

Normally you pull the vacuum line and if there's gas or it smells like gas the FRPS is bad. It could be on the way out if there's a pending code that hasn't set yet. I had one blow so bad that when I removed it I was able to blow through it.

Cool I will check that out too. Just talked to my bother in-law, who is a mechanic. He thinks it is a vacuum leak somewhere because the fuel trims are so high at idle, like +25.

 

[CudaCobraSVT]

So finally took it to my Mechanic a while back and my transmission shop had swapped the upstream O2 Sensor cables. They said on cylinder bank was way lean and one was way rich. No wonder it ran like crap!