Idle surge trial and errors

See the "Surging Idle Checklist for help with all your idle/stall problems. The first two posts contain all the updates to the fixes. At last count there were 24 possible causes and fixes] for surging idle/stall problems. I continue to update it as more people post fixes or ask questions.

Any codes? the strong exhaust smell sounds like something with the 02 sensors because thats what mine does when I was only running 1.....

Pull the codes and reset the idle and tps like the thread says and it should do something

Code 29 - Vehicle Speed Sensor (VSS) is an electronic sender mounted on the speedo pickup gear
on the trans. It works the cruse control for both 5 speed and auto trans cars. The VSS is used to tell the
computer to speed up the idle as you slow to a stop. This helps keep the engine from stalling when you
slow down for a stop sign or stop light.
Check to see if the electrical connector is plugged into it. Clean the connector & contacts with non
flammable brake parts cleaner prior to replacing the sensor, as that may fix the problem. The sensor cost is
under $30 and it is easy to replace.


Code 51 Engine Coolant Temperature (ECT) sensor signal is/was too high -
Possible bad ECT sensor, or wiring. Possible missing signal ground –
black/wire wire broken or bad connection. With the power off, measure the
resistance between the black/white wire and battery ground. You should see
less than 1 ohm. Check the same black /white wire on the TPS and MAP
sensor. More than 1 ohm there and the wire is probably broken in the harness
between the engine and the computer. The 10 pin connectors pass the
black/white wire back to the computer, and can cause problems.

Pin 7 on the computer - ECT signal in. at 176 degrees F it should be .80 volts

Voltages may be measured across the ECT by probing the connector from the rear.
Use care in doing it so that you don't damage the wiring or connector.

50 degrees F = 3.52 v
68 degrees F = 3.02 v
86 degrees F = 2.62 v
104 degrees F = 2.16 v
122 degrees F = 1.72 v
140 degrees F = 1.35 v
158 degrees F = 1.04 v
176 degrees F = .80 v
194 degrees F = .61
212 degrees F = .47 v
230 degrees F = .36 v
248 degrees F = .28 v

Ohms measures at the computer with the computer disconnected, or at the sensor with the sensor disconnected.

50 degrees F = 58.75 K ohms
68 degrees F = 37.30 K ohms
86 degrees F = 27.27 K ohms
104 degrees F = 16.15 K ohms
122 degrees F = 10.97 K ohms
140 degrees F = 7.60 K ohms
158 degrees F = 5.37 K ohms
176 degrees F = 3.84 K ohms
194 degrees F = 2.80 K ohms
212 degrees F = 2.07 K ohms
230 degrees F = 1.55 K ohms
248 degrees F = 1.18 k ohms

Diagram courtesy of Tmoss & Stang&2birds



See the following website for some help from Tmoss (diagram designer) & Stang&2Birds (website host) for help on 88-95 wiring http://www.veryuseful.com/mustang/tech/engine/

http://www.veryuseful.com/mustang/tech/engine/images/IgnitionSwitchWiring.gif

http://www.veryuseful.com/mustang/tech/engine/images/fuel-alt-links-ign-ac.gif

http://www.veryuseful.com/mustang/tech/engine/images/88-91_5.0_EEC_Wiring_Diagram.gif

Code 67 - clutch not depressed (5 speed) or car not in neutral or park (auto) or A/C in On position
when codes where dumped. Possible neutral safety switch or wiring problem. This code may prevent you
from running the Key On Engine On tests. You can generally ignore this code, since it has no effect on
engine performance.

The computer wants to make sure the A/C is off due to the added load on the engine for the engine
running tests. It also checks to see that the transmission is in Neutral and the clutch depressed (T5, T56,
Tremec 3550 & TKO)). This prevents the diagnostics from being run when the car is driven. Key On Engine
Running test mode takes the throttle control away from the driver for several tests. This could prove
hazardous if the computer was jumpered into test mode and then driven.

The NSS code 67 can be bypassed for testing. You will need to temporarily ground computer pin 30 to the
chassis. Computer pin 30 uses a Lt blue/yellow wire. Remove the passenger side kick panel and then
remove the plastic cover from the computer wiring connector. Use a safety pin to probe the connector
from the rear. Jumper the safety pin to the ground near the computer.
Be sure to remove the jumper BEFORE attempting to drive the car!!!

Code 85 - CANP solenoid - The Carbon Canister solenoid is inoperative or missing. Check vacuum
lines for leaks and cracks. Check electrical wiring for loose connections, damaged wiring and insulation.
Check solenoid valve operation by grounding the gray/yellow wire to the solenoid and blowing through it.

The computer provides the ground for the solenoid. The red wire to the solenoid is always energized any
time the ignition switch is in the run position.

Charcoal canister plumbing - one 3/8" tube from the bottom of the upper manifold to the rubber hose.
Rubber hose connects to one side of the canister solenoid valve. Other side of the solenoid valve connects
to one side of the canister. The other side of the canister connects to a rubber hose that connects to a line
that goes all the way back to the gas tank. There is an electrical connector coming from the passenger side
injector harness near #1 injector that plugs into the canister solenoid valve. It's purpose is to vent the gas
tank. The solenoid valve opens at cruse to provide some extra fuel.

It does not weigh but a pound or so and helps richen up the cruse mixture. It draws no HP & keeps the car
from smelling like gasoline in a closed garage. So with all these good things and no bad ones, why not hook
it up & use it?


Code 95 Key O, Engine not Running - the following test path is for 86-90 model Mustangs.

The 95 code is because at one time or another, the fuel pump relay hiccupped and didn't provide power the
pump when the computer told it to run. Sometimes this is a one time thing, other times it is a no run or
runs poorly condition.

To help troubleshoot the 95 code, follow this link for a wiring diagram http://www.autozone.com/images/cds/gif/large/0900823d80167162.gif

Using the diagram, check the red/black wire from the fuel pump relay: you should see 12 volts or so.
If not, check the inertia switch: on a hatch it is on the driver’s side by the taillight. Look for a black rubber
plug that pops out: if you don't find it, then loosen up the plastic trim. Check for voltage on both sides of
the switch. If there is voltage on both sides, then check the Pink/black wire on the fuel pump relay: it is the
power feed to the fuel pump. No voltage there, check the Orange/Lt blue wire, it is the power feed to the
fuel pump relay & has a fuse link in it. If there is good voltage there & at the Pink/black wire, swap the relay.


Some Mass Air conversions neglect to run the extra fuel pump wire, and they always have a 95 code.
See http://www.stangnet.com/tech/maf/massairconversion.html for more information on the
Mass Air wiring conversion.

Fix the code 67 and the engine running codes will dump. Usually you just have to push in on the clutch and
make sure the A/C is off when you dump the codes.

None of The codes you posted pointed to a MAF related problem.

If you have a Cold Air Intake or aftermarket MAF not matched to the injector size, you could have a MAF related problem and not get a MAF code (code 66).

too rich of an idle will cause surging, seeing how you are running 24s on a stock tune i would check in that area... perhaps putting stock injectors and MAF back on to see if it clears it up... that will let you know whats wrong.

The ECT is necessary to help the computer set the proper air/fuel ratio.

A trip to Home Depot can help you find some brass fittings to mount the ECT directly in the intake manifold if you don't want to use the heater supply tubing.