Engine Idle cuts out

claypoolxx · Mar 7, 2026

Hi. I have what I think is a little different than the regular idling issues. My 93 5.0 has started to randomly cut out for a second at idle when warm. I haven't noticed it at all while driving. It doesn't surge or stumble, it just seems like it doesn't get a signal for half a second and then goes right back to how it should be. I've had to replace the TFI module because it caused to car to randomly shut off while running. Its been good for a while and now this.

I thought it was the same issue so this time I got the relocation kit and a new TFI. No change.

From what I've read it seems like a IAC or vacuum issue would make the car surge or stumble. This is like the power is cut for a fraciton of a second. To be honest, I'm not great at electric so if there are a couple cheap parts I can throw at it before I have to read a voltmeter I'd rather do that. Any ideas?

AeroCoupe · Mar 7, 2026

Have you checked for ECU codes? The check engine light (CEL) only flashes for emissions related codes so other codes can be present and the CEL will not show.

claypoolxx · Mar 7, 2026

I have a code reader I could use tomorrow.

claypoolxx · Mar 9, 2026

I just have an emission code that has always been there.

AeroCoupe · Mar 9, 2026

You could be loosing the profile ignition pickup (PIP) in the distributor. It is a Hall effect sensor that the ECU uses to determine injector pulses and the TFI to fire the coil.

Did you use thermal paste between the TFI and the heat sink? If so what kind?

Last time you did a tune up on the car? This would be plugs, rotor, cap at a minimum. Last time you replaced the plug wires (what brand and type) and fuel filter?

claypoolxx · Mar 9, 2026

I don't drive the car much unfortunately. Don't know the brand of plugs, but they have less than 1000 miles on them. Wires are motorcraft and have the same 1000 miles. Cap and rotor are unknown, they were on the car when I got it 6 years ago.

I bought the relocation kit and a new TFI. I mounted it on the wheelwell behind the passenger headlamp. It acts the same before and after the relocation kit and new TFI. But it does seems like its losing a signal for a brief period. Doesn't surge or hunt, juts occasionally seems drop for a second and go back to normal.

I haven't noticed it while driving. Is that signal from the distributor a little weaker at idle? I guess a cap and rotor would be a good idea anyway though.

AeroCoupe · Mar 9, 2026

If the plugs are not Motorcrafts I would replace them as well. What about the fuel filter? Did you use thermal paste when mounting the TFI to the heatsink?

General karthief · Mar 9, 2026

If this is an occasional low RPM skip like hummmmm ba hummmmmm ba-ba kinda thing most definitely get a new cap and rotor.
JMO

claypoolxx · Mar 10, 2026

General karthief said:
If this is an occasional low RPM skip like hummmmm ba hummmmmm ba-ba kinda thing most definitely get a new cap and rotor.
JMO

Yes. Not consistent. Once every 5-10 seconds, sometimes longer.

General karthief · Mar 10, 2026

Sounds like, as I type this I think 'that's a dumb thing to start out a written response ', I think you've got a spark plug wire, distributor cap/rotor or plug jumping to ground, get up in the middle of the night, take it for a ride, feel it act up, pull over in a dark spot lift the hood, no flashlight, leave it running, look for 'spark skatter' or arcing around plug wires, plugs/boots at the head or headers, basically anywhere a plug wire touches can/will bleed spark, may take a few minutes of looking, you may hear a snapping noise unless you gots them heater pipes.
Distributor cap gets really 'dusty' on the inside, actually that's like tiny welding slag dust and it builds up and will cause 'spark skatter' inside and weaker spark outside, replace rotor at the same time.
If that don't help buy a GMC style blower and stick on there.

claypoolxx · Mar 12, 2026

I ordered a cap and rotor to put on. Even if that's not the cause, I'm not sure how old they are. It has gt40 aluminum heads and I do remember researching quite a bit about what plugs to get, but offhand I forget what they are. I did use the thermal paste on the TFI and it is now mounted off of the motor. I'll double check the wires and how they are routed. Hopefully I can take it out this weekend and to check for sparks. It will only do it after it is driven some and then idles. Won't do it if I just let it idle in the driveway.

AeroCoupe · Mar 13, 2026

Just for clarification if they are aluminum then they are GT40X heads. GT40 and GT40P’s are cast iron.

JD1964 · Mar 14, 2026

My 92 had random cut off a few times right before the ECU failed from corroded capacitors. Once the ECU failed, obviously it was a dead in the water no start condition.

Checking the ECU for corrosion on the capacitors is relatively easy to do.

claypoolxx · Mar 16, 2026

I haven't had a chance to replace the cap and rotor yet, hopefully tomorrow. The rain should wash the salt off the road too. I had the ECU rebuilt a few years ago so I really hope thats' not the problem.

claypoolxx · Mar 24, 2026

Cap and rotor have seemed to have fixed it. Haven't had a chance to take it on a long drive and get it real hot, but I think I'm good. I appreciate all the help.

alutwon · May 18, 2026

Mine has been doing the same thing for a few years now. Its idling at 650 then wham, drops to 200-300 it usually catches itself but not always. TFI is relocated to the front radiator support. newish cap, rotor and distributor. Spark plugs and wires about a year old. It only happens when its warmed up and only after idling for a few minutes, like at a drive thru for example. Only thing i haven't touched is the fuel pump but since this only happens at idle and never when at speed, i figure it would be worse at speed.

AeroCoupe · May 18, 2026

Have you checked for codes and/or vacuum leaks? Have you done a base idle reset?

alutwon · May 19, 2026

AeroCoupe said:
Have you checked for codes and/or vacuum leaks? Have you done a base idle reset?

no codes, no vacuum leaks that I can find, base idle reset has not been done in a while.

I noticed today driving it, that the rpms seemed to sink lower and lower as the heat crept up sitting at the traffic light. I recently relocated the tfi but that same tfi sat in the original location for about a year, maybe the damage is already done.

General karthief · May 19, 2026

What are the gauges doing when idle drops?

CAMTWO1070 · May 25, 2026

Most dont know that too much lateral movement within the distributor shaft can translate into idle fluxuations and issues idling and FYI the TFI module isnt the only thing prone to overheating ...;- The Halls Effect sensor is inside the EMI/RF chamber where the spark is hot n heavy and the heat combined causes issues when the magnets in the pickup dont detect the reluctor wheel good enough too or if theres been too much damage to the distributor shaft bearing due to camshaft walk...

If you pop the distributor cap and attach a magnetic indicator base to a spot that it will attach to and just touch the rotor with the tip ,zero it out then twist the rotor back n forth youll see the amount of total runout .

When you look at the bottom of this distributor from my 88 Mustang LX you can see how much aluminum was worn away causing my issue...My runout was at .038" and my bottom bushing had alot of side play too..I got it with 202k and it never saw a T-Chin replacement either and after doing the required maintenance it was running killer..

Tolerance limits are between .005" and .015" of lateral travel.

While youre there you should also check the T-Chain deflection for excessive slack and that requires a hefty 1/2" socket wrench and a cheater bar to turn the crank back n forth to see the slack..

Back n forth tolerance shouldnt have any more than .050"..If you have more than .050" freeplay in your crank before the rotor tip moves you need a new timingchain..........

View: https://www.youtube.com/watch?v=4_f5ukZVri8&t=1s

I bought a new distributor off AutoZone and set it in place tightened down the holddown bolt and checked lateal runout again with the digital dial indicator and this time the runout was set at .030" from thenplace that made it.

I pulled the gear and the collar and shimmed it until I got .005" on the new distributor and the thing was purring like a baby tiger as I had to pull the shaft and shim the upper part until the lateral slack was at .005"..

I also did the TFI module relocation at the same time and for close to two years the things been running pretty sweetly...

When the distributor isnt within specs and good the timing becomes erratic and this not only causes the TFI module to get a lil hotter than normal and cause running and idle issues but it does this to the ECU itself aswell from all the recorrecting it ahs to do to stay in sync.

So if your vehicle has over 130k miles and youve never done the recommended T-Chain replacement along with new waterpump and thermostat plus new front crank seal between 80k and 120k chances are youre gonna also need a new thrust plate installed especially if its a 5 speed model...Just installing a new distributor to replace one that had too much lower bearing side play wont fix the issue it will be just a temporary bandaid.

My 351w in my worktruck has 255k miles and has had two T-Chain replacements along with waterpump ,T-Chain and seals and each time the Timing Chain had alot of stretch and comes with the territory when theres a manual transmission present in a 4200lb vehicle with a 1 ton payload limit..I also replace the $13.00 thrust plate aswell for added insurance each time too......

Nobody really takes the time to realize the camshaft spins twice as fast as the crank and that all the springs combined create a rotating force that takes alot of exertion to get it moving and that job is given to a single chain up front....

If they designed engines to have two t-chains one front and one rear then the forces would be more equalled out but have alot of pressure to turn it..

My 351w has like 80lbs of spring pressure closed and like 250lbs open on just 1 valve and theres 16 of them along with 16 lifters and 16 pushrods with 16 rocker arms rocking at 1.6:1 ratio.....

Nothing lasts forever and somethings gotta wear down...........LOL

Good Luck

Engine Idle cuts out

Member

lube between the nut and the face. I know my lubes

Member

Member

lube between the nut and the face. I know my lubes

Member

lube between the nut and the face. I know my lubes

wonder how much it would cost to ship you a pair

Member

wonder how much it would cost to ship you a pair

Member

lube between the nut and the face. I know my lubes

there is enough sticking out to grab on to

Member

Member

Member

lube between the nut and the face. I know my lubes

Member

wonder how much it would cost to ship you a pair

Active Member

Similar threads

Privacy & Transparency

Privacy & Transparency