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Discussion Starter · #1 ·
Hi guys, I started having an issue the last few years when the car was at operating temperature and I shut it off, when I would go to start it, revs would go up upon start and then drop really low to the point where it would almost stall. Sometimes I would have to blip the throttle to keep it from dying. When I took it out of storage this spring, the issue is even worse. On cold startup, no issues whatsoever. Cold idle is around 1100 rpm or so and drops down to around 700 rpm. Once warm, if I go to start it (stop for gas for example), revs climb like normal on startup and then drop so low it stalls. One time it did it 4 times in a row. Reading online, looks like something to do with the Throttle Bypass Valve (IAC). Can a good cleaning solve the issue or is this a case where it needs to be replaced and have the computer relearn? Any advice would be appreciated!
 

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if it was the bypass valve, it wouldn't rev up, and come down

have you ever touched the throttle stop on the stock throttle body?

run engine on and off codes
 

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Discussion Starter · #3 ·
I've never touched the throttle stop at all (yes I have a stock throttle body).

Don't have a clue how to pull codes on my car (never had to!). I'll have to read up on that.
 

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Smoke test.
If you have never messed with the throttle stop, it’s more likely to be a vacuum leak than the IAC.
 

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Discussion Starter · #5 ·
Thanks for the replies. I’ll try the following:

1 - pull codes as Indy mentioned. Besides this stall on warm startup, car runs great so I would be surprised to see codes but you never know.

2 - I’ll check all the vacuum lines for any cracks and connections. I recently replaced the lower intake gasket (coolant in oil) but doubt that install caused any issues as the car is behaving the same way as it did before the install. I obviously don’t own a smoke tester so I may be forced to bring it to a shop for that.

3 - try to clean the Throttle Bypass Valve. It’s never been pulled before so it must be pretty dirty. Since I’m pulling the upper intake to re-torque the lower, I might carefully try to clean the throttle body also. I guess I have to be careful with regards to the TPS sensor?
 

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I’d get a can of Powerfoam and spray while she’s running once she was warmed up. Let her sit 10-15 min to soak it in, then take her for a spin. She’ll choke and sputter but all sorts of blue smoke will fog the neighborhood if it was dirty. Then she‘ll run better If that was a issue. I hear seafoam can work similarly But I’ve never used it. I have used the other for 30yrs nearly.

As Indy said, run your KOEO and KOER codes. Report back with results.
 

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Discussion Starter · #7 ·
I’d get a can of Powerfoam and spray while she’s running once she was warmed up. Let her sit 10-15 min to soak it in, then take her for a spin. She’ll choke and sputter but all sorts of blue smoke will fog the neighborhood if it was dirty. Then she‘ll run better If that was a issue. I hear seafoam can work similarly But I’ve never used it. I have used the other for 30yrs nearly.

As Indy said, run your KOEO and KOER codes. Report back with results.
Good idea on the powerfoam. If I can’t easily find that I’ll get Seafoam. I’ll report back on codes. What happens if I run the KOEO and KOER checks and have no codes. Will I see any flashes?
 

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Good idea on the powerfoam. If I can’t easily find that I’ll get Seafoam. I’ll report back on codes. What happens if I run the KOEO and KOER checks and have no codes. Will I see any flashes?
At a minimum, you will get code 11 (all clear). Flash-pause-flash.

If you don't get any flashes at all, then you have other issues.
 
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Discussion Starter · #9 ·
Alright, ended up getting an OBD1 code reader and got the following codes:

KOEO - 23 and 67
Continuous Memory - 11
KOER - 23

Looks like for 23, TPS is out of range.
For 67, Neutral drive switch circuit failure, circuit open or A/C input high

I also bought a can of Seafoam Top End Cleaner.
 

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Discussion Starter · #10 ·
Ran KOEO in gear and got 23 and 67 but then in neutral, only 23.
 

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so the ecm is saying you have a circuit problem with the 23

take a volt meter and check the circuit

could be a faulty sensor, or the wiring
 

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That’s because it looks for neutral during part of the test.

use a multimeter, probe the TPS and check it for smooth operation/signal.
Repair as necessary
Clear the codes/ retest/ drive the car

if the problem persists, smoke test it
You can build a smoke test setup for literally $5
 

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Discussion Starter · #13 ·
Ok so here's what I got with key on engine off:

orange - 5.08V (have power so that's good!)
green - (idle) ~0.66V, WOT ~4.59V

I guess at idle the voltage could be a little higher but it seems to be in range (0.5V - 1.25V). At WOT, 4.59V seems high (should be ~2.71V above idle from the little I read).

Not sure what else to do. I checked all vacuum lines for proper connections or any cracks. All checks out. I was planning on cleaning the IAC and running seafoam through the TB while the engine was running and at operating temp to see if that will do something to improve the situation. As Hybred suggested, a smoke test might be in order, I don't know.
 

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Code 23 is telling you that the sensor is out of range.
0.66v is out of range
WOT starts around 2.7v, and should continue to rise smoothly up to 5v

there should be a smooth voltage increase all the way through the range.

why are you not sure what to do next?
Don’t jump around. TPS + Smoke test.
 

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Ok so here's what I got with key on engine off:

orange - 5.08V (have power so that's good!)
green - (idle) ~0.66V, WOT ~4.59V

I guess at idle the voltage could be a little higher but it seems to be in range (0.5V - 1.25V). At WOT, 4.59V seems high (should be ~2.71V above idle from the little I read).

Not sure what else to do. I checked all vacuum lines for proper connections or any cracks. All checks out. I was planning on cleaning the IAC and running seafoam through the TB while the engine was running and at operating temp to see if that will do something to improve the situation. As Hybred suggested, a smoke test might be in order, I don't know.
at 0.66v measured at the TPS, you are on the edge

remember the ecm is getting that reading, after it passes through connectors and wires until it reaches the ecm

measure at the ecm, you could have sufficient drop to be out of range.
 

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Discussion Starter · #16 ·
Good point on the losses along the way to the EEC processor. I'll check pin 47 and see what voltage I get. If it's well below, is it a matter of loosening the TPS and rotating it (CW or CCW?) to up the voltage?
 

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TPS should not be adjustable

you can try, but i would eliminate any voltage drop first

one lead at tps, other lead at ecm, key in run, check drop

you still have an air leak......

so tps should be addressed after you fix the air leak
 

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Discussion Starter · #18 ·
With all the key on tests i've been doing, put the trickle charger on the battery and it was low. Left it on for ~4 hours and tried to take the voltage tests again:

Key on - TPS idle 0.679v, pin 47 on EEC connector 0.22V. I even sanded some paint off the frame so I could get a good ground for pin 47. Looks like I have considerable losses in the circuit.

I noticed my PCV valve hose under the upper was pretty loose with no clamp so I put one on. I'm going to take the car for a ride to get the battery charged up and then I'll give it one more test. Once I have my numbers, I'll try rotating the TPS to see if I get some miracle voltage increase (shot in the dark here).
 

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you should always place the meter's ground on battery negative

that will help identify drops on the ground side of the circuit

if you have ground side drop, you will also have to find it, and address, power side drops are only half the equation
 
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Discussion Starter · #20 ·
When I did the TPS check, the black lead on my multimeter was on the negative battery terminal. Unfortunately with the EEC connector, can't get that far. I did put a jumper cable on the negative of the battery and touched the other end with the black lead but didn't make a difference. I guess to check the grounds, perform a resistance check on each ground that I can find with the actual chassis? Any open loops and I'll simply remove the cable, clean and try again? I hate electrical but I'm definitely learning a lot. Thanks for your help!
 
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