95GT Ignition Issue - Stumbles when cold

I'm looking for some advice from you 5.0 guys out there, with an ignition issue on my 95GT.

The car has aprox 70K miles on the clock, it's a 5 speed, and I had the car tuned this spring to solve an engine ping problem. New wires, cap, rotor, and fuel filter. The IAT and MAF sensors both cleaned up.

The car has been running great, until recently when the weather has turned cool. The engine has been 'stumbling' at all points through the RPM range. If the problem occurs when the car is just idling, it usually stalls the car.
When driving, the rpms will suddenly drop by about 2-300, then bounce right back up. This might happen once, or happen repeatedly. When the car is cold, it does this quite often. As the car warms up, the problem slowly goes away...after aprox 25 mins of driving it runs perfectly.
The car jerks, and feels like it's missing on two or more consecutive cylinders.
I get no Check Engine Light at all.

If the problem continues to get worse, it will soon be undriveable. I've tried swapping out the Throttle Position Sensor, and the problem persists.

The local Ford Dealer think's it could be the IAC valve, but that wouldn't account for the problem occuring at wide open throttle, would it?

I suspect an ignition system problem.
I pulled the new dist. cap off, vacuumed all of the fine metal particles out, and noticed that the PIP is loose, and moves around quite freely below the rotor. Is that normal? I would have to remove the entire distributor assembly to get a closer look, but this is slightly more complicated than I feel comfortable with, and may not be the problem.

The fact that the problem goes away when the engine gets heat soaked must be a clue, but I can't afford to start changing components randomly.

Any ideas guys??? I really can't afford to take it to a shop right now, so I'd appreciate any suggestions for where to start looking.

Thanks in advance,
-Cold 5.0

Good info, thanks!

I will certainly check out the two temp sensors, but I don't believe they're at the root of the problem. The engine gets up to full temp within 10 mins, and I have the problem for at least twice that long. I don't have a code reader, but I'm sure I borrow one.

The problem seems to go away when the engine gets heat soaked, which leads me to believe that something inside the engine bay is loose when cold, but as it heats up, the component expands from the heat to the point where it fits snug again, and works properly. This could be a sticky valve that loosens up when the temp rises, a vacuum leak, or an electrical contact. If it's an electrical contact, I will definitely need codes to find THAT needle in a haystack.

Does anybody feel that this could be an EGR issue? It seems unlikely, and that's one of the things they checked during my tune up this spring. It's worth asking the experts out there for an opinion though!

Also....I dropped by a website called fordfuelinjection.com, and they talk about a TFI (thick film ignition) module mounted on or near the distributor. I find no mention of this item in my manual, only a reference to the ignition module located under the air cleaner box. Are these one in the same? They look completely different, though in all fairness, the picture on their web site may not be from a Mustang.

HISSIN50 said:

Welcome to the boards!

What kind of volume of metal-shavings did you have in the dizzy bowl? That and a loose PIP are not acceptable.

When the dizzy bushing starts to go, it often takes the PIP with it. I'd find a friend with a spare dizzy and toss it in. It's not hard to install and remove dizzies.

The hot vs cold thing is interesting. Have you felt the slop in the PIP and mainshaft when cold vs hot? I wonder if thermal expansion takes some of the slop out, hence it running better when warm.

That is if it's not tune related...................

Good luck.

Click to expand...

There was alot of metal particles in the bowl. I vacuumed them all out weeks ago when I first suspected the distributor. The problem persisted.

The distributor shaft wasn't loose at all...it was very firm, yet the PIP was VERY loose. Maybe 1/8th to 1/4 inch of deflection. You could feel it even without pulling the entire distributor out. Today, I pulled the whole thing out to have a closer look. The bushings on the distributor were all fine, but for some reason, the PIP collar over the shaft was worn out! I replaced the PIP with a new Borg Warner piece, and it fit like a glove. No movement at all...as you'd expect.

I put everything back together, and hoped for the best. Tonight, the car is running PERFECTLY! The stumbling is gone. It was a warm day though, so I won't be completely satisfied that I nailed it until it runs fine on a cold day.

Interestingly enough, the PIP in my GT is actually listed as a Cobra part. The part for the GT didn't look anything like what I had on my car. Thought I'd point that out for anyone else with a similar situation. I guess Ford was using up surplus parts.

Hardest part of the repair was pulling the drive gear off the distributor shaft. I chose to replace just the PIP instead of the entire distributor...$40 vs $140. Took me just under 2 hrs. start to finish.

I'll post an update if the problem returns. If it doesn't, I'd like to thank everybody for their help and support!!