Have you pulled trouble codes yet?
Some codes don’t make MIL to come on.

Last edited by Nos681 (10/25/2020 10:00 PM)

One of the beautiful things about the EECIV is its ability to keep running.  It will run with most any one sensor unplugged.  It simply goes back to a default program using other parameters.  Its not going to be ideal, and may not be smooth, but its not going to leave you stranded either. 

Now 65to93 I need to understand your setup.  Is this a problem that just started?  What's been done to the engine?  I'm curious why you have a 75mm TB. 

Did you just plug in the MAF after it was running?

Might have to disconnect battery and restart.

From my understanding, the ECM will determine baseline for all sensors upon initial  power up.
If you just plugged in sensor afterwards, the amount of change could affect it. 
Might even have some codes recorded as well.

Thanks all for your input:

Engine - 302 cu, cobra intake, aluminum heads, mild cam, MSD 6al box, MSD ignition coil
Codes: 11, 67, 81, 82, 84, 85 
11 - System Ok
67 - NSS circuit failure - makes sense I currently don't have one 
81, 82 - air diverter solenoid failure
84 - EGR vacuum regulator 
85 - canister purge solenoid 

Since these codes are mostly smog related, I believe that a ecu is getting a faulty reading from a sensor.  

Sorry for the confusion: I have a 70mm TB but the MAF is calibrated for a 75mm. My understanding is that the MAF calibration should be a bit bigger than the TB. 

It seems Bullet Bob's theory aligns with the question I had about the MAF - I was reading 1.2 v at idle which, according to this, is the equivalent of running at 20ish mph. There could be some fan wash on the MAF, but when I hold a box in between the fan and the MAF, there is no change. 

In the thread I linked, one person mentioned that the tps could have an affect on the MAF reading, is this possible? Do you all have any suggestions on how to lower the MAF voltage so that it reads correctly at idle?

I wonder if its worth putting the car on a dyno. 

Thanks!

Last edited by 65to93 (10/26/2020 5:07 PM)

The TB is too big for your application.  This doesn't explain you idle situation, but it can help explain other issues.  The problem is that the surface area of the throttle plate is significantly larger than stock.  The MAF can't be calibrated for this.  You have to tune the TPS based enrichment in the ECU.  Without doing that you will have fueling issues.

Based on your other changes I'm also going to recommend that you get the car tuned, because "calibrated" MAFs usually don't work 100% right on stock foxbody applications.  Your tuner should also be able to iron out the idle.

Alternately you can pick up a wideband O2, and something like the Moates Quarter Horse and software to tune it yourself.  If you never plan to mess with the combination again it may not be worth it, but if you do then it will pay for itself by avoiding further trips to the tuner. 
 

The TB is the right size for a cobra air intake. I appreciate the tuning recommendation, I'll do some research on that option. 

Raymond - When I unplug the IAC, the engine stumbles or wont run if the base idle screw is not touching the plate.  It is interesting that you say this  " it's very common practice for people to try to adjust the idle screw like they would a carb setup which foul up the operation of the IAC."  because I have been following the base idle reset procedure. So I have been messing the with idle screw a lot.

Let me know if any this brings any thoughts to mind or tests to try! It sounds like this could be a bunch of things that aren't quite working together to run efficiently.  

 

Just because the Cobra intake has a 75mm hole in it doesn't mean you need to run a 75mm TB.  It hurts nothing for the TB to be smaller than the opening in the intake.  The Cobras used a 65mm TB.  10mm doesn't seem like much, but its the surface area difference.  4,430 sq.mm vs. 3,317 sq.mm.  That's over 1,100 sq.mm difference and more importantly, its a difference of 34%. 

Bullet Bob wrote:

TKOPerformance wrote:

Just because the Cobra intake has a 75mm hole in it doesn't mean you need to run a 75mm TB.  It hurts nothing for the TB to be smaller than the opening in the intake.  The Cobras used a 65mm TB.  10mm doesn't seem like much, but its the surface area difference.  4,430 sq.mm vs. 3,317 sq.mm.  That's over 1,100 sq.mm difference and more importantly, its a difference of 34%. 

That's a point I had trouble convincing some guys years ago when it came to drilling jets.  .001 makes significant difference and .005 makes a huge difference.  People seem to forget about Pi...or maybe then never learned about it.

Yeah, I mean, I'm only running a 70mm on my 331 that's going to be in the 450HP range when done.  75mm is WAY overkill for anything other than a giant engine, super high RPM smaller engine, or forced induction. 
 

65to93 wrote:

The TB is the right size for a cobra air intake. I appreciate the tuning recommendation, I'll do some research on that option. 

Raymond - When I unplug the IAC, the engine stumbles or wont run if the base idle screw is not touching the plate.  It is interesting that you say this  " it's very common practice for people to try to adjust the idle screw like they would a carb setup which foul up the operation of the IAC."  because I have been following the base idle reset procedure. So I have been messing the with idle screw a lot.

Let me know if any this brings any thoughts to mind or tests to try! It sounds like this could be a bunch of things that aren't quite working together to run efficiently.  

 

OK if you've been following that procedure then you're good. I mean you do have to adjust it some, but a lot of folks go in and just start cranking on the idle screw.

What is your fuel pressure at idle? And was it checked with the vacuum line off? Also what base (SPOUT out) timing are you running?

One thing I'd try, is unplug the IAC and then turn the set screw until the car idles. Make note of the RPM. Then disconnect the battery long enough to reset the computer then reconnect everything, See what happens, I am thinking you'll have a high idle, but maybe not.

There's always this item as well, people have used them for years on finicky idle cars. https://lmr.com/item/LRS-9939A/1986-93-Mustang-50L-58L-Idle-Air-Control-Iac-Adjuster

Kind of a long shot, but what's your battery voltage at idle?