My '95 F250 has a 120k mile engine in good health.. For about 2-3k miles it has had some really strange issues.. When I bought it at about 112k miles it sometimes got the rolling idle these trucks were known for from time to time but for the most part ran great. 90% of the time it had a solid idle.. Now it gets a high idle sometimes but calms down, other times it has a slight surge.. The really strange thing happens when it gets a high idle surge. And it's like 1,500 down to nothing and back rapidly.. No codes and the truck is still drivable it's just annoying.. The fact the IAC is controlling it that rapidly tells me the IAC itself is working

It had a slight missfire which I cured with a Summit racing tuneup .. I ordered MSD cap/ rotor, Ford Racing 9mm wires, Street Fire coil and a Summit CDI box. Oh and Autolite 25 plugs. I only needed a new cap, rotor and plugs but it just sounded good

I was going to LS swap this truck but I actually just got engaged and so, I had a ring expense and whatever else my fiancee wants. she's a car chick so somewhat expensive... Truck may get long tube headers eventually but only because she will want it to sound good, or rather I could justify it to her

I'm thinking the ECM is bad, and finding a 302 5spd speed density ECU might be a tall order

 

Well good luck on all counts!
Not sure if it's the ECM or not, but if it comes down to you not being able to find one (I think they're still out there, but sometimes not all the time) then once you get some more money you can always go with a PimpX from Stinger Performance. There's another discussion here just today with some details, but basically it's a custom brain inside a stock Ford enclosure so your stock harness plugs right in. It's programmable to your satisfaction so you can tweak if for the headers if needed, and any other mods too.
It's not like a $200 reman unit of course (more like closer to a grand I think) but it's a cool option for enthusiasts.

Anyway, back to the top in case anyone else knows what it might be. At this point it would be great if it just turned out to be a bad connector on a sensor!

Paul

 

A rolling idle is rarely caused by a bad PCM. Vacuum leaks, bad TPS, sticking throttle cable, leaking throttlebody, are the most common causes. Many times it is one cause stacked on top of the other. Intermittent high idle can be a bad sensor that the computer is compensating for.

Warm up the engine then run the Key On Engine Off (KOEO) tests and Stored Code display.

 

PimpX is on my want list but out of budget right now. My old boss has a slew of EEC Ford ECU's but they are not labeled.. I'm pretty sure that because it's a 1995 and an F250 that it will be an HO/351 firing order speed density ECU and that a '95 150 would be MAF correct?

 

It does not display anything.

 

Not outputting codes is one of the signs of a possible failed ECU but it's not definitive. There are an infinite number of ways a failed ECU can act from complete failure/no run condition to very minor issues. Just depends what component inside the ECU failed.

 

X2....no codes is a sign of a bad computer assuming you initiated the test mode correctly.

 

not all 95 F150 302's are MAF, they were speed density also, and your 302, has the 351w firing order, check firing order, and wire routing, to make sure.

1,3,7,2,6,5,4,8 make sure 1, 3 dont cross each other, and 5, 6 dont cross each other

 

It's not "bad", just poor decision making skills.

 

I think the SD F150 302's were federal emissions and I'm in NY where we always have had CARB vehicles... I could be wrong.


The distributor is routed correctly. I pulled the wires all off and did them off the diagram/ firing order and they don't cross. This cured the misfire. It has better response and power now, it's just an IAC doing the wrong things now pretty much. Still drivable but annoying

 

gyngerbredman had same issue with his, not wanting to idle down when coming to a stop, his IAC was new(not motorcraft) replaced, his issue went away, have you attempted to clean yours/

 

Sorry but still hung up on buying/installing the “Summit CDI box”. Was there money burning a hole in your pocket?

Its pretty easy to tell if you have speed density or mass air. Do you have a mass air meter or not?

 

The CDI box was cheap enough and I figured multiple sparks couldn't hurt. I know it's not needed.. The whole tuneup made a big difference in how it runs. Starts quicker now, almost with just the pop of the key

And it's speed density but it's an F250 302 so that is somewhat uncommon in the '95 year range for a new ECU. F150's of that era were mostly Mass air

 

sometimes the IAC operates rapidly though.. I'll clean/ change it with OEM in case it's broken

 

My truck with the stock ignition system also fires right up with a quick turn of the key.

That was determined by the transmission. Someone correct me if I’m wrong but only computer controlled ( E4OD/ 4R70W ) transmission trucks were mass air. The rest were still speed density.