Engine Idle issues, tracing vacuum lines

[John Birone]

What vacuum lines are required on my 87 5.0 with ac and smog pump removed? This was converted to mass air. No idle issues when I parked it 20 years ago. Now it will start instantly and hold the idle, but once it’s warm it stalls coming to a stop. I’ve replace a couple of caps at the tree and inspected the lines I can see. I guess removing the upper intake is next to see what’s going on under there… Thanks all.

 

[General karthief]

That's the best way to find broken vacuum lines.

 

[John Birone]

I capped the branch marked AC. I assume that’s okay, and it ran fine, but just want to make sure and also remove as many lines as I can. Anything else unnecessary with my setup? No cats, either.

 

[KRUISR]

Auto or manual transmission? Original setup or converted? Sitting 20 years you cleaned MAF, TB, IAC and new base idle reset?

 

[John Birone]

Original manual (SSV, or SSP as they seem to be called now). Has MAF setup and computer from a ‘93. Didn’t mess with anything else as it runs great and holds a perfect idle every time I start it. Just drops low and stalls after warmup when I come off the gas to stop. I can feather the gas while breaking and usually keep it running, but that’s no fun. The vacuum lines are old, with a lot of cracks in one of the caps I replaced. I expect to find more under the upper intake. It was run sporadically over those 20 years, so didn’t sit the whole time. Last ran about 5 years ago.

 

[Mustang5L5]

have you dumped codes?

When you performed the mass air conversion, did you wire in the VSS? Mass air cars need the signal from the VSS as part of their logic, but in 87-88 it was only used for cruise control. The two wires to the ECU on pin 3 and 6 must be added. If there is no VSS signal, a common symptom is stalling when the vehicle comes to a stop.

This is a common step missing from most mass-air conversion instructions including LMRs. It tends to be intermittent, but happens enough that this step really shouldn’t be overlooked.

 

[John Birone]

Have not dumped codes, ordering a reader now. Also did NOT wire the VSS, but I swapped the entire engine harness from the 93 to my 87. I can check, but it should have been included. I’m not entirely familiar with the VSS though. I could use more info. Where should I have run the wires? My car does not have cruise, either. Thanks!

 

[AeroCoupe]

If you do a search it will come up multiple times.

 

[Mustang5L5]

The VSS wiring is part of the dash harness, and not present on the 87-88 mustangs at all.

The wiring goes from the transmission to an 8-pin connector in the drivers side kick panel. I can get you wire colors later on. From there it heads up to the cruise module. All you would need to do is tap into the two wires and put them into pin 3 and 6 on the ECU.

Since your car never had cruise, you don’t even have a VSS sensor. So unless someone added it for some reason, you will need to get the sensor, and the correct speedo cable and install. On my ‘88, the VSS harness plug was clipped to the crossmember. After putting the VSS in (my car also didn’t have cruise) I found the two VSS wires in the drivers kick panel and ran two brand new wires to pin 3 and 6.

I know, total pita which is why most people don’t do it. Some folks never had an issue, and some do. I did mine right from the start, so I never got to see if mine really needed it.

I can provide more info on wiring locations if needed.

 

[John Birone]

I need a new speedo cable anyway, or at least a new gear. Pointer jumps all the way past 140 and buries itself until I put the car in reverse. Then it goes the other way. Odometer still works. I also have a Tremec 3550. Is the VSS still be an option? Really appreciate the information!

 

[AeroCoupe]

You used the speedo sensor off your T5 and put it into the 3550, correct? The VSS is just a different version of the speedo sensor that has the provision to plug into it with the VSS wiring. Looks like this one:

https://lmr.com/item/LRS-9731BB/mustang-speedo-sensor-hardware-kit-83-93

You can find them cheaper if you search.

 

[John Birone]

Yes, that’s correct. I need to change to accommodate the 3:73 gears and fix my Speedo anyway, so perfect time to make this upgrade. Will a code show to verify this?

 

[evintho]

This might be helpful. Here's a pic of the underside of the upper intake showing the vac hose routing on my '93.

As for the VSS issue, do as Mustang5L5 suggested. Add a VSS then get the proper VSS connector........

1979-2004 Mustang Speed Sensor Pigtail Wiring Connector at Transmission | eBay

•Fits ANY 1979-2004 Mustang or Cobra. •Kit includes an OEM style plug and wiring pig tail to connect to the original harness. •7" long wiring for easy splicing. Any problems must be reported within 48 hours of receipt.

www.ebay.com

Run 2 wires to pins 3 & 6 on the '93 ECU. Pin 3 is the speed sensor signal, it's circuit #679 an 18ga grey/black wire and and pin 6 is the signal return, it's circuit #676 an 18ga pink/org wire.

 

[89notchDude]

The VSS wiring is part of the dash harness, and not present on the 87-88 mustangs at all.

The wiring goes from the transmission to an 8-pin connector in the drivers side kick panel. I can get you wire colors later on. From there it heads up to the cruise module. All you would need to do is tap into the two wires and put them into pin 3 and 6 on the ECU.

Since your car never had cruise, you don’t even have a VSS sensor. So unless someone added it for some reason, you will need to get the sensor, and the correct speedo cable and install. On my ‘88, the VSS harness plug was clipped to the crossmember. After putting the VSS in (my car also didn’t have cruise) I found the two VSS wires in the drivers kick panel and ran two brand new wires to pin 3 and 6.

I know, total pita which is why most people don’t do it. Some folks never had an issue, and some do. I did mine right from the start, so I never got to see if mine really needed it.

I can provide more info on wiring locations if needed.

I have an 89 and I removed the cruise control module. Will this affect me the same way as the OP?

 

[Mustang5L5]

I have an 89 and I removed the cruise control module. Will this affect me the same way as the OP?

No. The wiring splits off so the ECU still gets a signal even if the cruise modules is removed. There are cars that were ordered without cruise control so it would be no different.

If the ECU doesn't get a signal, it generates a code 29 if you want to double check.

 

[Mustang5L5]

Yes, that’s correct. I need to change to accommodate the 3:73 gears and fix my Speedo anyway, so perfect time to make this upgrade. Will a code show to verify this?

No VSS input to the ECU would be a code 29

 

[John Birone]

Okay code geeks, I have a list. Keep in mind I have no smog pump, VSS is ordered, and I replaced the fuel pump relay after replacing the entire tank, pump, pickup and fuel lines at tank.

KOEO - 67, 85, 95
C - 14, 29, 33, 63, 66, 67, 85 & 95

I looked them up, and 85 scares me a bit. I advanced the timing decades ago and am running premium, but I guess I better check that again.

What’s with all these circuit failures? Car has been running good other than the idle issue.

Thanks!

 

[Mustang5L5]

Okay code geeks, I have a list. Keep in mind I have no smog pump, VSS is ordered, and I replaced the fuel pump relay after replacing the entire tank, pump, pickup and fuel lines at tank.

KOEO - 67, 85, 95
C - 14, 29, 33, 63, 66, 67, 85 & 95

I looked them up, and 85 scares me a bit. I advanced the timing decades ago and am running premium, but I guess I better check that again.

What’s with all these circuit failures? Car has been running good other than the idle issue.

Thanks!

Sorry i didn't respond sooner.

Some of those codes don't seriously affect how the car runs. So lets go through them one at a time.

Code 67- This code usually pops up if the NGS harness on top of the T5 is not connected. Often times i see this when folks AOD-to-T5 swap a car and don't hook it up because the AOD trans harness does not have the plug for it, or folks assume its not needed at all and never hook it up to begin with. It;s wired in parallell with the clutch switch, so if you rerun the codes with the clutch pedal pressed in the entire time, and it clears, then you might have an issue with the NGS circuit out to the T5

Code 85 - Canister purge circuit. The charcoal canister on the pass front fender. Is it removed?

Code 95 - fuel pump circuit failure. Common code when cars are mass air swapped and do not add the fuel pump monitor wire fuel pump relay to pin 19. Nuisance code you will always have unless you run the wire

Code 14 - Ignition pickup (PIP) was erratic – the hall effect sensor in the distributor is failing. Bad sensor, bad wiring, dirty contacts. You have to press the distributor gear off the shaft to replace the sensor. The pip signal is used for ignition timing and fuel injector timing. This one you will want to troubleshoot

Code 29 - No VSS input. We already talked about this one. ECU needs a VSS input or may stall at times

Code 33 - EGR no flow. Is your EGR deleted?

Code 63 - TPS voltage too low. Typically this means that the TPS voltage at the ECU is under 0.5 volts. Keep in mind this is a CM code, so it could be old and the condition has cleared. I recommend erasing codes, running the engine a few start cycles and then retesting to see if this code is still present.

COde 67 - covered that above. Try running codes with clutch pedal held down start to finish.

Code 85&95 see above.

 

[John Birone]

Thank you! Charcoal canister is removed, along with the cats. Can’t remember what I did with the EGR valve 20+ years ago. What is the proper way to delete that?

I’m going to clean the contacts on the distributor as this thing sat for a couple of decades. If that doesn’t do it, I’ll replace the entire thing. Probably time anyway.

I’m running a Tremec 3550, and again can’t remember if I had an extra connection that didn’t get plugged in. I’ll re-run with the clutch depressed and see what happens.

I did not add the fuel pump monitor wire when I did the mass air swap. Pin 19 on computer to which location on the fuel pump relay? Interior is stripped bare, so easy to add this kind of stuff right now.

I slotted the tps holes decades ago for the “free HP” (yes, I fell for that), so I’ll measure and see if I can adjust it within range, or replace if I can’t. Again, likely needs to replaced due to age and the conditions it was stored for 20+ years.

Thanks again, and let me know about the EGR delete process so I can clear that one!

 

[Mustang5L5]

I did not add the fuel pump monitor wire when I did the mass air swap. Pin 19 on computer to which location on the fuel pump relay? Interior is stripped bare, so easy to add this kind of stuff right now.

Pin 19 to the load side wire of the fuel pump relay out to the pump. So on a 1987, that would be the pink/black wire.

I do not believe the 3550 has the provision for the NGS on top, so it's likely not hooked up.

For the EGR, with the code present it is turned off in the ECU, so not much more to do. You can build a resistor pack to permanently disable it and eliminate the code. It's hard to find the male plug as there is a crackdown on everything EGR related. If you can find a male connector plug, this is the resistor arrangement.

Also, since you have the interior apart, would be easy to make the check engine light functional on your car as 87-88 mustangs did not have a working CEL. Just need a bulb and one jumper

Electrical - Foxbody Mustang: Adding Check engine light to 86-88 cars

As some may know, the early Speed Density 86-88 5.0 cars did not come with a functional Check engine light. The 86 cars never had the means to display a CEL. The 87-88 cars do have a spot for the CEL under the tach, and part of the dash wiring. This, however, was solely for the 2.3L Mustangs...

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