'71 Bronco w/ '91 Mustang 5.0 Idle Stall Surge Problem

yearofthebronco · Oct 2, 2010

Hi guys,
I have a '71 Bronco with a '91 Mustang Gt 5.0 HO Motor in it.
It was left sitting for a while before I owned it and it now has this idle surge and stall problem. From a cold start it will race up to 1700-1900 rpm and after about 30 seconds or so slow down to 800-900 before dropping and surging a lot then usually stalling. It also seems to run rich. Ive been trying to tackle this problem on my own but cant seem to and definitely need some help. Everyone on this site seems really knowledgeable any help is appreciated

I have already:
Replaced the IAC
Cleaned the MAF
Cleaned the 10pin connectors
Cleaned the throttle body
Replaced spark Plugs
reset the idle computer

Should I buy a ford scanner to get the codes on it?

ransil · Oct 2, 2010

You can get a cheap scanner, not any OBD* type scanner or use a paper clip & a test light..

http://www.allfordmustangs.com/Detailed/2006.shtml

or a link to links

http://www.explorerforum.com/forums/showthread.php?t=191861

ransil · Oct 2, 2010

Get codes first no shooting in the dark..EECiv is pretty stupid so don't expect much from codes but you need to start somewhere...

what harness are you using??

how is pin 30 connected this is the NSS terminal??

what computer are you running?

any mods to the motor?

Post pics of you engine compartment..

did you set the idle per instruction or just disconnect the battery?

ponyracer · Oct 2, 2010

I've noticed in all the 5.0's I've had that there very sensitive to grounds. Check that all the grounds that are supposed to be on the harness are there and clean.

Greg_B · Oct 2, 2010

Without codes it is anybodys guess... but if I were to guess I would say pin 30 is not connected properly or the grounds are not good. OR... the computer could be shorted out. I repaired the short in mine with a tiny piece of wire and a soldering iron.

Greg

ransil · Oct 2, 2010

Greg_B said:
the computer could be shorted out. I repaired the short in mine with a tiny piece of wire and a soldering iron.

Greg

which is caused by pin 30 being connected wrong..

00gyrhed · Oct 2, 2010

does it get better once it is hot?

I soldered my 10 pin connectors, made a big difference in the idle. But this sounds like coolant sensor.

firehawk · Oct 2, 2010

I had to replace my battery before I could get my F.I. 5.0 to run decent.

Some drill an 1/8 hole in the throttle body blade to let a small amount of air past it to idle better but it seems like a bandaid to a problem.

Broncobowsher · Oct 2, 2010

Pull codes first.
Next, unplug the MAF and see how it runs in limp mode. Sounds like you could still have a MAF issue (installed backwards, gone bad, air entering the engine not going through the MAF, etc).

You replaced the IAC, it bolts on 2 ways. Get it backwards and it won't work correctly. That is also a very likely cause.

00gyrhed · Oct 3, 2010

Hell using an old style will cause a lot of problems. I chased a lot of inconsitantcies until the old alternator when out and I repleced with a new syle. Cleaner power signal means better ffedback from sensors.

yearofthebronco · Oct 3, 2010

Broncobowsher said:
Pull codes first.
Next, unplug the MAF and see how it runs in limp mode. Sounds like you could still have a MAF issue (installed backwards, gone bad, air entering the engine not going through the MAF, etc).

You replaced the IAC, it bolts on 2 ways. Get it backwards and it won't work correctly. That is also a very likely cause.

Scanner coming in the mail
With the MAF unplugged it'll surge and doesn't idle worse
With the IAC unpluged it'll surge and doesnt idle worse

yearofthebronco · Oct 3, 2010

00gyrhed said:
does it get better once it is hot?

I soldered my 10 pin connectors, made a big difference in the idle. But this sounds like coolant sensor.

When it's warmed up it gets a little better but overall doesn't make much of a difference. Ill shift it in to reverse and it'll stall or I'll shift it from reverse back into drive with my brakes on and it'll stall too. Anything that makes rpm dip lower than 900 stalls it out.
Will look into coolant sensor

Broncobowsher · Oct 3, 2010

Where do you have the base timing at?
IF you have it cranked up, set it back to the 10° with the spout out, reset minimum airflow and TPS, see what happens then. I keep dealing with people cranking the timing up to "get more power" and the engine dies out under the slightest load at idle. Back the timing off and it will run at idle a lot better.

yearofthebronco · Oct 7, 2010

ransil said:
Get codes first no shooting in the dark..EECiv is pretty stupid so don't expect much from codes but you need to start somewhere...

what harness are you using??

how is pin 30 connected this is the NSS terminal??

what computer are you running?

any mods to the motor?

Post pics of you engine compartment..

did you set the idle per instruction or just disconnect the battery?

I am very new to broncos and to car mechanics in general. Ive only worked on my vintage motorcycle, no fuel injection or computers and a whole bunch of other stuff.

Out of those questions I can only answer:
I set idle per instruction as on modded mustangs site.
I dont know harness or computer.
What is pin 30?

Just got Codes!!...?
So it says its testing 6cyl but its 8cyl???
also got 21, 94, 44, 33, 18 then it repeats itself.
Can anyone tell me what these mean and how I can start to tackle this?

I am having trouble posting pictures so heres a link

http://s754.photobucket.com/albums/xx189/heyitsderek_photo/bronco engine bay/

ransil · Oct 7, 2010

are those EFI valve covers?

what is that hose onto of the throttle body connected to??

Oil type air filters can contaminate a MAF sensor..

av bronco · Oct 7, 2010

On your computer it has a letter/number combo, like A9L, what is your comp. number?

yearofthebronco · Oct 7, 2010

Broncobowsher said:
Pull codes first.
Next, unplug the MAF and see how it runs in limp mode. Sounds like you could still have a MAF issue (installed backwards, gone bad, air entering the engine not going through the MAF, etc).

You replaced the IAC, it bolts on 2 ways. Get it backwards and it won't work correctly. That is also a very likely cause.

Pulled the codes and got pics of engine compartment

yearofthebronco · Oct 8, 2010

av bronco said:
On your computer it has a letter/number combo, like A9L, what is your comp. number?

It is indeed the A9L

jw0747 · Oct 8, 2010

good info on this web site. you said you reset the computer. look at Section 3 below and check to see if you did it going thru the same steps. mine was doing like yours then I reset the computer and that cured it. good luck

http://www.muscularmustangs.com/iac.php

'71 Bronco w/ '91 Mustang 5.0 Idle Stall Surge Problem

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