erratic throttle/acceleration

[lifeinthesouth]

Holy crap, i had an interesting ride home tonight. First a little background...
95 5.0/e4od, I just installed all new balljoints and alignment cams and fabbed up and installed my engine crossmember for the shock towers. I had the battery disconnected while tacking the crossmember up. Drove it about a 1/2 mile under 20 mph and ran fine.
This morning I drove it to the dealer for an alignment and aside from it wandering all over the place it ran fine... i pick it up this afternoon and the alignment is great BUT...
after i get about a mile from the shop i start getting a lurching feeling so i drive a bit further, decellerating and accelerating, to see if i was imagining things... and there it is... i let off gas and coast and it accelerates on it's own then i approach a hill and press the gas to go up and it runs fine, i let off while still going up and it feels fine then start going downhill and it does it again.
SO it's not happening under load and will do anything from intermittent blips of the throttle to a steady prolonged acceleration on flat or descending surface. (kinda like setting cruise control)

I went back by the dealer to question if they'd done anything else and the service mgr said no and came out with me to see if i could recreate it... we took it down the street and it's still happening so we go back and pop the hood he checks the IAC (iirc) by disconnecting it and nearly stalling out the truck which he states is what it should do and that if it kept running fine it would be a vacuum issue. He said since the battery had been disconnected it may need to go through a couple warm-up cycles to reprogram.

I'm not getting a CEL so does that mean it's not throwing a code?
The ground strap from the bottom of the header panel to the frame is disconnected but has been for a couple weeks without issue.

You guys have any ideas, ever experienced this, is the dealer full of it?
Maybe i bumped something loose when messing around under the hood???

[AussieRod]

Since you just fitted an over the engine crossmember, perhaps your accell linkage is bumping against it on over-run and cruise, maybe due to a broken engine mount. On accelleration, the throttle body moves down due to engine torque reaction, and up under any decelleration. I would check all your clearances and make sure none of your accell parts are touching the brace when the engine is running. You would be surprised just how much the engine can move even with good mounts under power and over-run. Also check you didnt drop a spatter ball into your wiring and cause a short out (ask me how I know that)

[lifeinthesouth]

Those were a lot of my first thoughts but it doesn't explain driving into town with no ill effects at all.
Definitely gonna do some rootin' around under the hood today... it was late/dark last night when i got back so wasn't able to see anything right off the bat.
I just wanted to throw the question out for feedback ideas. Thx Aus!

[damon1272]

The manager is wrong about the ICS. You should be able to unplug it and have it idle fine or only see a slight drop in idle speed. Otherwise there is a learned condition in the processor. I would make sure the throttle body and ICS is cleaned then reset the processor and see if it comes back.
To reset the processor drive the truck to get it warm, unplug the the the positive battery cable for 10 min. Before reinstalling the cable turn the lights on and step on the brake pedal to deplete the capcitors in the processor. Restart the truck and let idle for five minutes, then turn on all the accessories like the lights, radio, and A/C to put a load on teh engine and electrical system. Then take it out for a five mile drive. Let it see a good WOT. Processor will be reset. Then see if it comes back.

[lifeinthesouth]

i'll give that a shot Damon. i took off and cleaned the IAC valve yesterday and it was a mess, tons of carbon buildup and very sticky. After cleaning it moved better but still seem to drag; i suppose since it's spring loaded it should snap back and forth pretty quick. I've got a new IAC coming tomorrow.

[lifeinthesouth]

Found it... after installing my coil buckets there was a wire loom near the fuse box and the shock tower rubbed through it creating a short.
That explains the completely erratic behavior. contact, no contact and so on!
It was one of my first thoughts when it originally happened i just didn't dig into it enough. Of course i didn't discover it until after i had finished all the troubleshooting cleaning i did tonight.
needless to say, i now at least a a very clean throttle body and idle control valve... i'll probably see an mpg increase considering how bad they looked.

[AussieRod]

Glad you found the problem Sometimes it just takes a good look around in good light to see the issue.