Stutter below 3k RPM and erratic idle

[imnotacop420]

So I have been fighting this problem for a while now, I don't drive the car much so I didn't worry too much about it.

The car either idles below 500 RPM or between 1500-2000 RPM, and I also get some hesitation below 3000 RPM when driving. If you are getting on it in the high RPM range there is also a strong smell of fuel. The car sits the majority of the year, and I only put between 1000-3000 miles on it during the summer. If it sits for a while, or if I disconnect the battery to reset the PCM, it will stall out the first couple times I start it up. I have checked for vac leaks by spraying carb cleaner, found nothing. I have replaced IAC and PCV, still same problem. Intake gaskets probably have around 10-15k miles on them. Plugs and wires are probably around 5 years old, but I would say have maybe 10-12k miles on them. If I have the AC on the idle is up around 2000-2200RPM

Searching around seems a lot of people suggest replacing plugs/wires and cleaning the MAF, but I think it needs tuned.

Car is a 2.5 with 167,000 miles
Mods
MSDS Headers
EGR Delete
Optimized Mustang TB
Throttle Body Spacer
Max Extrude Honed UIM
Sho-Source LIM
75mm MAF housing (with stock sensor)
BAT intake pipe
Taylor 9mm plug wires
I think that's it engine wise

when I got the MAF it was calibrated for a returnless style fuel system, I have a return style fuel system. After doing some research I found where some people were using their stock sensor in the larger housing without any issue, so I went that route.

I also have one of those MAF calibrator things, but I haven't hooked it up or played with that as I figured I would want an A/F gauge before I started turning the knobs on that sucker.

CEL is obviously on for headers and EGR delete

Thoughts/suggestions? Anything I can try before I take it to a tuner?

Thanks!

 

[gmorrell]

Stock ECU, no tune? If the EGR is deleted and you didn't tune around it, you will likely have some part-throttle driveability issues. EGR is inactive at idle and high load, it's only active during part throttle warm cruise, which might explain some of the issues you're seeing below 3,000 RPM. EGR is funny stuff and you have to tune for its presence or absence. EGR that's not there when it's supposed to be will cause the engine to stumble or surge, EGR flow at idle will stall the engine dead.

MAF's aren't calibrated for return or returnless fuel systems, they're calibrated for the full scale mass flow that occurs when the MAF output is at 5V. If you take the electronics from a 65mm body and put it on a 75mm body, the full scale flow at 5V is different and you have to re-scale the load tables in the ECU.

If you put the stock MAF electronics in a 75mm housing, it's likely under-reporting mass air flow to the ECU, sooooo, might be a lean stumble. Part throttle acceleration requires adding fuel, and if the MAF is under-reporting air flow, it's probably lean during acceleration.

I would try the stock MAF housing with the stock electronics, reset the ECU, report back.

Part throttle stumble can also be plugs or wires. Have you looked at the plugs lately? Maybe pull them and tell us the color of the center insulators? Check the resistance of the plug wires while you're at it, most resistor wires will run about 3,000 ohms/foot.

 

[Beans]

I'd guess lack of tune as well. I'd put my money on the throttle body, swap for stock?

Did it the issue start when you installed the throttle?

 

[imnotacop420]

I can check the plugs, haven't looked at them recently.

I don't have the stock TB anymore. I installed the LIM, TB, and MAF all around the same time.

I'll start with putting the stock MAF back on, if that doesn't work I'll see if someone local has a TB I can borrow.

 

[squeek]

No Title

Just a tid bit, I bypassed my egr via this way about a year and a half ago. No cel.

 

[imnotacop420]

Just a tid bit, I bypassed my egr via this way about a year and a half ago. No cel.

I have the EGR delete kit, the y-pipe is capped off and I have the delete plate on the UIM. What would I do with the DPFE lines coming off the EGR pipe, nothing and route the EGR line back to the DPFE sensor?

 

[squeek]

The green line that goes from the egr to the vacuum solenoid. You route out from the solenoid to the dpfe and into the lower port on it. The dpfe takes small samples of the air. You're just giving it a little vacuum.