Off idle studder

A

a1machinista1

Active Member
Sep 2, 2023
112
22
28
Oregon
#1
Just bought the 89 GT, I've been waiting to post after I get some diagnostic done. But today it fixed itself for a few minutes.
This has a studder off idle that feels like an imbalance in the rotating assembly. Today after work I warmed it up for 3 mins and headed home. It drove perfect, no studder no shutter or vibration. 4 miles home from work and at my last stop from home before shifting into second gear the idle went up to about 2k and CEL went on... so now it's back to studder off idle. Luckily I just got my obd1 reader from Amazon last night so I'm goi g to assume the code for the high idle will be in there. I'm not looking for someone to give me some kind of guess. I more or less just wanted to get this down before I forgot the scenario. I'm old!! I'll be back with some codes and an introduction along with the story of this rig.
 

  • Sponsors (?)


#3
Quick rundown of the car. I just bought it a couple weeks ago. 89Gt manual.
EFI no deletes except AC compressor.
It needed new license plates and registration but it would not pass emissions. Was 400/200 max HC at idle and 1200 HC at 2400rpm.
I gotca set of factory 19lb injectors and had them gone through.
I installed new plugs,njectors, changed throttle body and plenum gaskets. Replaced all vacuum lines under plenum from tree out. New thermostat, fan clutch, h20 sensor, new distributor, new o2 sensors, new fuel filter, new 130a alternator, new circuit breaker for alternator, new starter solenoid, new batter cables new iac, did baseline reset and then retested emissions, it passed with flying colors, 92/200 HC at idle sovthey did not check at 2400 rpm. It has always had this studder off idle. Until today for a few minutes. It feels like a vacuum leak shake to me. I just bought a smoke machine so that will be done soon. Anyone care to point me in any direction? I have any and all tools available to me. I have a very experienced automotive background, however a tuner or "that guy" I am not.
 
#4
I just looked to get familiar with the components and check the condition of the vacuum lines. It looks like there is probably a reservoir under the pass fender? The vacuum lines definitely look original to the car. I'll go ahead and replace all the vacuum lines. Should I run continuous lines lines and bypass the 4x4 connector? Would you suggest silicone vacuum line or should I get the poly line with new rubbers? I also noticed that the egr valve position sensor harness plug has a broken retaining tab and is taped with electrical tape to the sensor.im thinking I can probably find a new connector and splice it in? I will go ahead and replace the egr and the egr vacuum regulator while I'm at it. I saw a post about testing resistance in this system. Would anyone be willing to run through that with me? My name I's Troy by the way. Thanks in advance
 
#6
After work I pulled the egr and new IAC to see is something was going on. I went ahead a verified the TPS and oddly it was at .56. I pulled it off and it looks like the drive dogs are tore up a bit. I deformed them to give a little more hold to them and reset it to .98 and ordered a new one which will be at my shop tomorrow a.m.. drove home fine. Still has the off idle studder but no more high rpm. Thursday I will look up how to test all the points of resistance and see what I find out.
 
#7

Help me create the "Surging Idle Checklist"

Updated 05 July 2022 to add rough idle when cold and smooth idle when up to normal operating temperature. See the EGR tech information, section #15 for more help. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank...
www.stangnet.com www.stangnet.com
This should help, it shows a step by step procedure for checking components involved, thanks to jrichker and others for the write-up.
 
#8
Ok thanks, I read through this and I can surely do all this in the coming days. One question though: I have the code 67 and I can not tell you if the car was in neutral when I checked fir codes, I can tell you with absolute confidence that I was not holding the clutch down so when the write up says I won't be able to dump the codes, does that mean like an ex wife that won't let go? The running codes will be there forever?
 
#9
a1machinista1 said:
Ok thanks, I read through this and I can surely do all this in the coming days. One question though: I have the code 67 and I can not tell you if the car was in neutral when I checked fir codes, I can tell you with absolute confidence that I was not holding the clutch down so when the write up says I won't be able to dump the codes, does that mean like an ex wife that won't let go? The running codes will be there forever?
Click to expand...
Try turning the A/C off and running the test again.
 
#10
After reading this I think it male's sense to have my 10 pin connectors in the best shape I can before I get knee deep in this. Before heading to work this morning I pulled the connectors up and squeezed them together really good and this thing ran like an addict on super meth. I think I have a good plan in mind.
 
  • Like
Reactions: 1 user
#13
Ok, all was off during codes. I hooked up the obd1 reader I just bought and put it on hold and disconnected the reader during the code reading. (What ever the manual said). Should that get rid of the 67 code? I have new tps and will install after work. Hoping codes are gone so I can get fresh codes if still a problem.
 
#14
If you still get a code 67 then you might need to get a look at your neutral safety switch. You may even need to insert a jumper.

I think we have instructions around here for this somewhere...
 
#15
from here:

Electrical - How To Pull Codes From EEC-IV In 86- 95 5.0 Mustangs

@Noobz347 - The code dump procedure isn't in the sticky - you may want to add it... Dump the codes: Codes may be present even if the Check Engine Light (CEL) isn't on. Dumping the computer diagnostic codes on 86-95 Mustangs Revised 26-July-2011. Added need to make sure the clutch is...
stangnet.com stangnet.com

jrichker said:
Dumping the Engine Running codes: The procedure is the same, you start the engine with the test jumper in place. Be sure the A/C is off, and clutch (if present) is pressed to the floor, and the transmission is in neutral. You'll get an 11, then a 4 and the engine will speed up to do the EGR test. After the engine speed decreases back to idle, it will dump the engine running codes.
Click to expand...
 
  • Useful
Reactions: 1 user
#16
Yesterday I installed the new Motorcraft TPS. It was not wanting to go below 1.30 volts I removed and reset it multiple times. After multiple tries it dropped right in at .99.. it's running much better. I did squeeze the salt and peppers together again and I'm assuming they are the biggest culprit. But it is running much better. This weekend I'll get the 10pins cleaned up and start thr resistance testing.
 
  • Like
Reactions: 1 user
#18
Still running decent, didn't get a chance to do anything on it today as it was in getting new rack and pinion with tie rod outers. The installer told me I need new ball joints. Mine are SUPER tight, he said they look low miles but are probably causing my tracking issues. Also my rack was in way better shape than I thought it was.
 
  • Like
Reactions: 1 user
#19
Got a chance to check resistance in egr paths. All was under 1 ohm. I did pull vacuum off of egr at idle to see what happened. Nothing changed but the vacuum hose from the EVR was "pulsing"? Kind of blowing and sucking at the same time.(?) I checked voltage at EVR red wire in idle and I was getting 12.3v.
I also rechecked TPS setting and it was at 1.06v. I could not turn it enough to get below 1.0v so I turned the housing that it bolts to on top of the TB and set at .99v. Now my studder is back...
Plan: squeeze salt and peppers
Redo a baseline idle reset @.99v
If still shuddering will go slightly above 1.0v to see what happens. I realize this may all be mute if I have 10-pin connection issues.
 
#20
Okay, let’s bust the TPS myth yet again. This is the condensed version but my understanding the EEC-IV will check for the following:

— Minimum voltage at closed throttle over .49 vdc. , less than .49 and codes 23 and 63 will set as failures.

— Max voltage closed throttle should not exceed 1.2 vdc, or codes 23 and 53 will set as failures.

With the TPS voltage between 0.5vdc and 1.19 there should be no codes and the EEC will use this voltage as the closed reference.

So with all that set the TPS voltage between 0.6 vdc and 1.1 vdc and you should be good to go. Typically you can put one on out of the box and it will be in this range.

All of this can be read here:

Mustang TPS Adjustment - 0.999999v not necessary

EDIT: This post applies to 86-93 5.0 Mustangs. Seems to be a common myth, so lets sticky a thread explaining how the TPS works. Jrichker has provided the basic TPS guideline to follow. But here's a snip of the A9L GUFB which is the programming logic. Pay attention to the part highlighted...
stangnet.com stangnet.com

Do a base line idle reset and leave it alone.
 
  • Like
Reactions: 1 user
You must log in or register to reply here.

Similar threads

keel
Engine Car is idling rough and cutting out
Replies
4
Views
678
Fox 5.0 Mustang Tech
keel
keel
Vulpes5.0
Car idles good, then VERY SUDDENLY dies
Replies
25
Views
2K
Fox 5.0 Mustang Tech
Vulpes5.0
Vulpes5.0
T
Engine Crank but no start 1990 LX 5.0
Replies
10
Views
2K
Fox 5.0 Mustang Tech
General karthief
General karthief
B
94 cobra possible idle issue?
Replies
11
Views
719
1994 - 1995 Specific Tech
Noobz347
Noobz347
Mr.Kelley
Engine Help hard/no start runs rough.
Replies
25
Views
2K
Fox 5.0 Mustang Tech
CAMTWO1070
CAMTWO1070
Top Bottom
Back
New
Hot
Menu