95Gt stalls only when warm

95GTS302 · Mar 15, 2023

Hey guys, got a recently new to me 95 gt 5.0/ 5 speed. It’s pretty much stock, but having an issue where it will drive awesome no issues until it gets up to operating temp and pretty much right when the T-stat opens up it seems to want to start stalling out at a stop light unless I two foot it and keep the pedal feathered until the light changes. Looking for any input on anyone who’s had similar issue. No check engine light popping on either? Thinking etc?, o2’s?, vacuum leak only showing it’s ugly head when warm?, iac?, tps? Also notice a slight vibration in the wheel when it acts up.

joemomma · Mar 16, 2023

I'd start with a base idle reset (google the proper procedure), and then a smoke check for vacuum leaks.

ttocs · Mar 16, 2023

I had a similar problem with mine and it turned out to be the wire harness to the tps sensor. One of the clips holding it in place broke and when the motor got hot it would loose contact and show up as my foot on the pedal. Get the motor hot and just grab and pull/tug on any harness you can find and see if the motor changes at all to isolate which one it might be. If you know of a harness with broken clips, start there.

maillemaker · Mar 16, 2023

My 1990 E350 with 460 would idle rough when cold. Turns out it was a bad Engine Temperature Sensor. Note this was a different sensor than the gauge temperature sensor. I don't know if the 5.0 is similar or not.

95GTS302 · Mar 17, 2023

joemomma said:
I'd start with a base idle reset (google the proper procedure), and then a smoke check for vacuum leaks.

Yes, I’m taking it up to my buddy early next week to use his smoke machine and see what we find and if it’s not a leak then start troubleshooting from that point.

maillemaker · Mar 17, 2023

I built a smoke machine following a youtube video. Made it out of a gallon paint can. Super simple after you buy some nichrome wire. You'll need an air compressor, of course.

ttocs · Mar 17, 2023

make sure you smoke it when the motor is hot

Maximum95 · Mar 18, 2023

95GTS302 said:
Hey guys, got a recently new to me 95 gt 5.0/ 5 speed. It’s pretty much stock, but having an issue where it will drive awesome no issues until it gets up to operating temp and pretty much right when the T-stat opens up it seems to want to start stalling out at a stop light unless I two foot it and keep the pedal feathered until the light changes. Looking for any input on anyone who’s had similar issue. No check engine light popping on either? Thinking etc?, o2’s?, vacuum leak only showing it’s ugly head when warm?, iac?, tps? Also notice a slight vibration in the wheel when it acts up. View attachment 24391

Beautiful car man! Sorry to hear you are having this issue. As a first step, I would agree with the base idle reset. It's a very common cure for many idling problems!

Typically this happens because the throttle stop is not adjusted properly, and the car is relying on the IAC to idle. The IAC is meant to supplement the idle when loads are engaged, such as air conditioning, power steering, and heavy electrical loads. When you start the base idle reset procedure, you may find that the car will not idle on the throttle stop alone.

Good luck! There are plenty of base idle reset procedure write ups out there.

Rod · Mar 21, 2023

95GTS302 said:
Hey guys, got a recently new to me 95 gt 5.0/ 5 speed. It’s pretty much stock, but having an issue where it will drive awesome no issues until it gets up to operating temp and pretty much right when the T-stat opens up it seems to want to start stalling out at a stop light unless I two foot it and keep the pedal feathered until the light changes. Looking for any input on anyone who’s had similar issue. No check engine light popping on either? Thinking etc?, o2’s?, vacuum leak only showing it’s ugly head when warm?, iac?, tps? Also notice a slight vibration in the wheel when it acts up. View attachment 24391

Until the engine is warmed up the computer has it in open loop and uses a fixed map for fuel & timing. Once warm it goes into closed loop and the sensors come into play, Mass Air, MAP, O2, Etc. Start by cleaning the Mass Air wires, I have had dirty wires cause bad/no idle more times than I can count, change out the O2 sensors, just do it, no idea how long they were in there and they have a service life. Next take off the IAC anc clean it with carb cleaner, they get clogged bad with carbon, this will most likely fix hunting idle problems.

95GTS302 · Mar 22, 2023

Rod said:
Until the engine is warmed up the computer has it in open loop and uses a fixed map for fuel & timing. Once warm it goes into closed loop and the sensors come into play, Mass Air, MAP, O2, Etc. Start by cleaning the Mass Air wires, I have had dirty wires cause bad/no idle more times than I can count, change out the O2 sensors, just do it, no idea how long they were in there and they have a service life. Next take off the IAC anc clean it with carb cleaner, they get clogged bad with carbon, this will most likely fix hunting idle problems.

Thank you for the info, I know the P.O said he cleaned the mass air and changed the iac but I’ll take that with a grain of salt and check both areas. Doing the smoke test tomorrow and then I’m hoping to have some time this weekend to start troubleshooting this issue. Overtime has been extremely plentiful lately and times limited but can’t complain lol.

95GTS302 · Mar 22, 2023

Thank you all for you advice/guidance guys much appreciated. I will definitely report back my findings and fixes.

95GTS302 · Mar 23, 2023

So quick little troubleshooting today, vacuum leaks all good didn’t find any, however mass airflow is definitely questionable, if I unplug the mass air it will stay running. So took the sensor out cleaned it and now it will at least try to catch itself before it actually stalls. but still I want to replace the mass air flow Im pretty sure that’s the culprit. Its a cheap Chinese piece of poop right now lol Trying to find a motorcraft 19 pounder mass air flow seems to be hard lol called 2 dealerships and it’s totally obsolete, and the auto value i usually use for the motorcraft parts have been on back order for months. Any suggestions on locating one? Really didn’t want to have to buy a new pro m/ BBk unit or anything like that.

Rod · Mar 23, 2023

I would try to Junkyard an OEM, but short of that Napa Auto,Autozone, Advance, O Reilly, any chain brand will work on a stock/ish engine. And they all have a warranty if it doesn't.

95GTS302 · Mar 23, 2023

Rod said:
I would try to Junkyard an OEM, but short of that Napa Auto,Autozone, Advance, O Reilly, any chain brand will work on a stock/ish engine. And they all have a warranty if it doesn't.

Gonna give the o Reilly’s a try I just know when I mess with the for iac’s on my fox & the lightning only motorcraft seem to work well.

Maximum95 · Mar 23, 2023

95GTS302 said:
So quick little troubleshooting today, vacuum leaks all good didn’t find any, however mass airflow is definitely questionable, if I unplug the mass air it will stay running. So took the sensor out cleaned it and now it will at least try to catch itself before it actually stalls. but still I want to replace the mass air flow Im pretty sure that’s the culprit. Its a cheap Chinese piece of poop right now lol Trying to find a motorcraft 19 pounder mass air flow seems to be hard lol called 2 dealerships and it’s totally obsolete, and the auto value i usually use for the motorcraft parts have been on back order for months. Any suggestions on locating one? Really didn’t want to have to buy a new pro m/ BBk unit or anything like that.
View attachment 24621 View attachment 24622
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I had a cheap MAF on my Mark VIII when I bought it. It was a remanufactured one. I didn't even know such a thing existed lmao! The car would idle fine, but would shut off when you tapped the throttle.

Motorcraft wasn't available for that either. RockAuto carries a Delphi MAF, which is an OEM brand for GM. I would reccomend that one, as it's available for the '95 GT as well. Fixed the problem on my Mark.

Your other option is to go aftermarket. I have a Pro-M MAF on my car. It's been great.

95GTS302 · Mar 27, 2023

Well so far it looks like the new MAF is the ticket. Haven’t had any stalling issues anymore when warmed up.

Maximum95 · Mar 27, 2023

Thank you for following up! Glad to hear you got it sorted out.

badass98svt · Mar 27, 2023

95GTS302 said:
Well so far it looks like the new MAF is the ticket. Haven’t had any stalling issues anymore when warmed up.
View attachment 24720

What brand is the new MAF?
I had a similar problem on my old '81, and it ended up being the ignition module (In your case, that would be the TFI).
Sounds like you got it sorted though! Well done.

95GTS302 · Mar 27, 2023

badass98svt said:
What brand is the new MAF?
I had a similar problem on my old '81, and it ended up being the ignition module (In your case, that would be the TFI).
Sounds like you got it sorted though! Well done.

Blue streak electronics. From o reillys