Engine Mustang 1995 GT - RPM fluctuating while driving and surging

Paulo Fli · Nov 7, 2019

Hello guys, so I stumbled across this problem and it's been a riddle, since I just took the car to my local mechanic and we were unable to identify the problem.

Here's what's going on: The CHECK ENGINE light is ON and after a couple of minutes driving, the RPM needle goes crazy and the car starts to shake a lot (surging). The exhaust even pops sometimes (backfire?) and all of this happens only while driving, never during idle. Speaking of idle, after a short drive the RPM won't fluctuate at idle, but will hang at a bit over 1000 RPM's and the engine sounds a bit weird. When the car is cold it idles fine (around 650 RPM's). Also, the car even died while I was driving, even though it was a single time and at a low speed. Anyway, it shakes A LOT (as you can see in the video). Spark plug/spark plug wires are good, fuel injectors are also good. We put a new ICM but the problem persists.

I was thinking maybe IAC? MAF? something on the PCM? Thanks in advance, here's the link to the video: View: https://www.youtube.com/watch?v=X25cQMrn1Ck

General karthief · Nov 7, 2019

Did you scan for codes?
check fuel pressure?

Paulo Fli · Nov 7, 2019

General karthief said:
Did you scan for codes?
check fuel pressure?

Still didn't check for codes because they didn't have an OBD1 scanner. I was thinking, maybe it's fuel pump related? Will check for fuel pressure.

Paulo Fli · Nov 8, 2019

General karthief said:
Did you scan for codes?
check fuel pressure?

No codes shown, I honestly don't know what to do anymore.

General karthief · Nov 8, 2019

Ok, when you say 'no codes shown' do you mean you got a code 11? Computers talk in codes, here is something that will help you out: NOTE read through the list so you understand and have the tools handy, do not skip around, the next step is dependent on the result from the previous one.

Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

forums.stangnet.com

Paulo Fli · Nov 8, 2019

General karthief said:
Ok, when you say 'no codes shown' do you mean you got a code 11? Computers talk in codes, here is something that will help you out: NOTE read through the list so you understand and have the tools handy, do not skip around, the next step is dependent on the result from the previous one.

Help me create the "Surging Idle Checklist"

Updated 26-Oct-2019 to clarify creeping idle RPM increase as the car is being driven. Many of you are familiar with the "Cranks OK, but No Start Checklist for Fuel Injected Mustangs" checklist and the No Crank Checklist. They are very effective in finding and eliminating the problems by use of...

forums.stangnet.com

I mean literally nothing, already gave up.

General karthief · Nov 8, 2019

Paulo Fli said:
I mean literally nothing, already gave up.

what do you mean gave up?
your computer may have a burnt trace. They can be repaired or replaced

Paulo Fli · Nov 9, 2019

General karthief said:
what do you mean gave up?
your computer may have a burnt trace. They can be repaired or replaced

OK now that's interesting, turns out my computer was a bit "messy", I'll see if I can repair it or buy a new one, thanks! BTW, is it really possible that all of this is caused by the computer?

General karthief · Nov 9, 2019

Yes but there may be something that caused the computer to take a dump. There also could be issues other than the computer. Remember these cars are getting old and things like vacuum lines and gasket s get brittle and leak. Some of the vacuum lines are plastic tubes and are prone to braking.
Are you in another country (Brazilia/Brazil)?
go through the checklist I linked, that should identify any potential problems, the 94-5 stuff are highlighted. Post here if you have any questions.

Paulo Fli · Nov 9, 2019

General karthief said:
Yes but there may be something that caused the computer to take a dump. There also could be issues other than the computer. Remember these cars are getting old and things like vacuum lines and gasket s get brittle and leak. Some of the vacuum lines are plastic tubes and are prone to braking.
Are you in another country (Brazilia/Brazil)?
go through the checklist I linked, that should identify any potential problems, the 94-5 stuff are highlighted. Post here if you have any questions.

That's right, i'm currently living in Brazil and I own a Mustang here, people call me crazy and they might be right, LOL. $7 gas, almost no parts (I have to import everything) and very few mechanics are able to properly service a Mustang. Also, I barely see other Mustangs on the road (they are as rare as a Ferrari in the US) but I know there are a few, even more than Europe if i'm not mistaken. Anyway, thanks for your help so far, still haven't checked for vacuum/gasket leaks, will do that.

One more thing I forgot to mention, I know the owner installed an explorer intake and probably new heads/cam, but i'm not 100% sure.

General karthief · Nov 9, 2019

Check out our technical/how to threads for how to identify your head/intake and other good stuff that can help you out.
got any pics of your stang?

Paulo Fli · Nov 9, 2019

General karthief said:
Check out our technical/how to threads for how to identify your head/intake and other good stuff that can help you out.
got any pics of your stang?

Thanks! I will check those threads later. Here's some pictures of the car:

Paulo Fli · Jan 2, 2020

General karthief said:
Check out our technical/how to threads for how to identify your head/intake and other good stuff that can help you out.
got any pics of your stang?

Finally bought a proper OBD I connector, got CODES 332, 311 and 314

Chythar · Jan 7, 2020

Do you still have the smog pump and EGR valve attached? The codes indicate a problem with those parts. If you've deleted the EGR and didn't add a tune to the computer, you'll have drivability issues. The EGR lets exhaust gasses back into the engine, but only when you're at part throttle (cruising). Which happens to be the same time you're having trouble.

Paulo Fli · Jan 7, 2020

Chythar said:
Do you still have the smog pump and EGR valve attached? The codes indicate a problem with those parts. If you've deleted the EGR and didn't add a tune to the computer, you'll have drivability issues. The EGR lets exhaust gasses back into the engine, but only when you're at part throttle (cruising). Which happens to be the same time you're having trouble.

Thanks for your help Chythar, turns out I also have code 214, which I suspect has something to do with the distributor (correct me if i'm wrong). Now, the car cranks but won't start, I can hear the fuel pump but I don't smell any gas

Paulo Fli · Jan 7, 2020

Chythar said:
Do you still have the smog pump and EGR valve attached? The codes indicate a problem with those parts. If you've deleted the EGR and didn't add a tune to the computer, you'll have drivability issues. The EGR lets exhaust gasses back into the engine, but only when you're at part throttle (cruising). Which happens to be the same time you're having trouble.

BTW the previous owner detached the smog pump, as far as I know the EGR stills there, maybe some dirt on it?

dcm0123 · Jan 7, 2020

Popping in the exhaust is usually caused by un-burned fuel in the exhaust exploding.
Un-burned fuel in the exhaust could be one or more cylinders not firing- an electrical issue.
The Ford distributors are known to have issues, both the pickup module and the Ignition Control Module (you replaced) degrade with age.
Disconnect and plug back in all connectors on the engine with exception of injectors, also check the MAF sensor (between air filter and throttle body). Check the connector on the control box (body control module) which is mounted on the back of your radiator. This module controls fuel pumps, cooling fans and possibly spark (not sure about spark).

The connectors themselves often go bad, had a problem with the computer coolant temperature sensor connector and the Ignition Control Module connector.

The surging could be another issue but I would start with the above.

Our car idle also hangs over 1000 when hot but will drop to about 850 within a few seconds. If this is what you are experiencing, I would not worry about it.

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General karthief · Jan 7, 2020

Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

www.stangnet.com

This is a step by step diagnostic procedure for a no start situation, the 94-5 specific stuff is highlighted. Read through it to get an understanding and then do it step by step. Take notes. If you get stuck on a step post it here on this thread and we can help you.

dcm0123 · Jan 7, 2020

General karthief said:
Cranks OK, but No Start Checklist for Fuel Injected Mustangs

Cranks OK, but No Start Checklist for Fuel Injected 5.0 Mustangs model years 1986-1995 A word about this checklist before you start: it is arranged in a specific order to put the most likely failure items first. That will save you time, energy and money. Start at the top of the list and work...

www.stangnet.com

This is a step by step diagnostic procedure for a no start situation, the 94-5 specific stuff is highlighted. Read through it to get an understanding and then do it step by step. Take notes. If you get stuck on a step post it here on this thread and we can help you.

Very informative link. Is "the constant control relay module" the same as the body control module? If not, where is this module found?
.

General karthief · Jan 7, 2020

It is inside the right front fender well near the air inlet, looks like you can pull the inner fender panel out.

Engine Mustang 1995 GT - RPM fluctuating while driving and surging

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