Vintage Mustang Forums banner

1 - 18 of 18 Posts

·
Registered
Joined
·
37 Posts
Discussion Starter #1 (Edited)
The 5.0 in my 66 with Ford "suit case" injection surges below a 1500 idle. So far I've checked for vacuum leaks and found none, replaced the idle air control valve, the MAF and the Throttle Position Sensor with no results. I know this is an early Mustang forum, but I thought I'd give the question a try here because of the extensive mechanical knowledge among forum members. Because of this problem, I'm seriously thinking about going back to a carb. Thanks for any advice.
 

·
Registered
Joined
·
68 Posts
Is it a Speed Density or Mass Air setup? Have you tried resetting the idle? This is a common issue with Speed Density mustangs.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #4
The injection set up is basically a early 90's Cobra, Mass Air. I've reset the idle and it doesn't smooth out until 1500 RPM which is too high in my opinion. I'm running Edelbrock heads and a mild Trick Flow roller cam.
 

·
Registered
Joined
·
1,409 Posts
Are you running a VSS? How about a check engine light to check for codes? It could just be that you need a tune for the heads and cam. I tried running the Ford EFI with a 331 and could never make the part throttle surge go away, so off it came.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #7
Are you running a VSS? How about a check engine light to check for codes? It could just be that you need a tune for the heads and cam. I tried running the Ford EFI with a 331 and could never make the part throttle surge go away, so off it came.
Yep, it already has to tune for the heads and cam, and there is no VSS. Thanks for asking.
 

·
Registered
Joined
·
4,726 Posts
You are looking at the right places. A rough idle is usually caused by a bad fuel mixture from a vacuum leak or IAC problems.

What ECU are you using?
Are you getting any trouble codes?
Have you checked your fuel pressure?
What IAC did you use?
I have had horrible luck with aftermarket IACs. Recommend you only use a Motorcraft unit (same with distributors)
What have you done with the EGR system. Many folks have idle issues if they bypass EGR.
Do you have all the vacuum ports hidden on the underside of the manifold plugged?
Have you run the self test?
Have you checked compression, base timing, etc?

Other items to check?
Ignition
Fan (engine temp)
EGR valve
PCS
Exhaust leaks
Thermactor system

I highly recommend the following book to understand the EEC-IV system
“Ford Fuel Injection & Electronic Engine Control” by Charles O. Probst

You can also ask for help at Corral.net. Lots of Fox body experts over there.
 

·
Registered
Joined
·
1,266 Posts
When I had a z cam in my cobra it did the same thing. I ended up finding a IAC plate that has adjustable bleed screws.




Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
68 Posts
If you haven't tried it yet, unplug the IAC and see if it stops. You'll most likely have to adjust the idle screw on the throttle body to keep it idling. But either way it might, at least, give you a answer. Then, what I would look at is the IAC voltage. If it is swinging up and down your idle is going to follow it.
 

·
Administrator
Joined
·
19,410 Posts
Another vote for focusing on the IAC.
 

·
Registered
Joined
·
1,266 Posts
Also, if you slot the holes in the TPS, you can make it adjustable and use a voltmeter to set the TPS. Also, when you set timing and such, do you have the SPOUT connector disconnected?


Sent from my iPhone using Tapatalk
 

·
Registered
Joined
·
68 Posts
He said the he has replaced it already. So if it is the IAC, the next step is figuring out what is causing it to swing. Of course, is he used a old, gunky IAC then that would explain it too.
 

·
Registered
Joined
·
1,235 Posts
What air intake are you using and how far from the TB is the MAF located? MAF sensors are sensitve about distance from the throttle body...changing that distance often causes idle surge and other issues(Speed density is better for non-factory cars if you have the ability to tune it with something like quarterhorse). Idle surge is always a pain because there are a half dozen potential causes.
 

·
Registered
Joined
·
707 Posts
Also, if you slot the holes in the TPS, you can make it adjustable and use a voltmeter to set the TPS. Also, when you set timing and such, do you have the SPOUT connector disconnected?


Sent from my iPhone using Tapatalk
X2

Also, what size injectors do you have?
You may need an adjustable/tunable MAF.
 

·
Registered
Joined
·
592 Posts
If it's been happening since the tune, what does the tuner say?
If the tune was good, I'd be guessing a vacuum leak, particularly under the upper intake as already mentioned.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #17
Thanks for all the help. As a consequence of your suggestions, I've replaced the (Standard Part) Idle Air Control Valve with a Motorcraft part. That smoothed things out considerably although the engine will surge if I set the idle too low with the idle adjustment screw. I've ordered an Idle Air Control Adjuster from LMR and will install it tomorrow to see if I can lower the idle a bit more. I'm pretty sure I've eliminated all vacuum leaks by replacing upper intake gasket and eliminating other possibilities. I'll post a follow up after I install the Idle Air Control Adjuster.
 

·
Registered
Joined
·
37 Posts
Discussion Starter #18
Hello everyone, and again, thanks for the help. I've been fighting my 5.0 fuel injection since my initial post with little success at bringing the idle down. Rather than making my skirmishes with the ancient Ford Obd1 system into an endless war, I've decided to replace it with an Edelbrock Pro Flow 4 because of its modern adjustability and the fact I can style the engine without the Ford "suitcase" upper intake.
 
1 - 18 of 18 Posts
Top