Tried "instant on" with my jeep. Odd results

[doclees]

So i tried shutting down the engine going down hills in my 95 Jeep wrangler. Got plenty of steering and brakes but upon starting up the engine went wild. Coughed and raced like crazy. No gas savings there. Any ideas why this happened?
I also tried popping the clutch to start it and bucked in an ugly way before smoothing out.

[deejaaa]

did you keep the clutch in or put it out of gear?

[doclees]

Best of my recollection clutch would have been depressed.

[Arragonis]

Scenario A could be because the ECU is detecting the car moving and is making sure the brakes, steering etc. are covered. A little like in some cars when you pop into reverse the ECU raises idle by ~2-300 rpm so you can idle into a space without stalling.

EDIT - the ECU will also take a little while to swap from cold to warm programs, maybe it assume cold at first and then swaps over.

Scenario B is pretty normal when popping the clutch to restart, it was kind of rough on my 1.0 3cyl petrol so I assume something bigger would be even less smooth. What gear did you use and at what speed ?

[doclees]

Clutch popping start up was at 40 mph in 5th. A nice easy 1200 rpms. I coughed, bucked and just seemed to object. Never a problem in other obd 1 cars I've owned in the past.
Using starter it didn't just add a couple of hundred rpms but more like 1k rpms.

If the ECU would assume a different setting after only about 30 seconds then I would think that is what is going on. Anyone have a get around for this?

[Arragonis]

I'm speculating really, I've had similar experiences in other cars - the Aygo was rough when bump started and the hire FIAT would do the RPM racing thing when it was restarted - I stopped using the technique as Mrs A complained - we were on holiday in Spain at the time and they drive on the right (aka the wrong) side of the road

[P-hack]

I know saturns will sometimes crank open the idle air control valve in an attempt to bring the idle back up when killing the engine. Can you warm it up and disconnect the IACV and see how it acts? (probably will be cranky when cold, but otherwise might help)

[doclees]

Originally Posted by P-hack

I know saturns will sometimes crank open the idle air control valve in an attempt to bring the idle back up when killing the engine. Can you warm it up and disconnect the IACV and see how it acts? (probably will be cranky when cold, but otherwise might help)

cant hurt to give it a try.

[vskid3]

When you bump start it, are you just lifting your foot off the clutch or do you lift it enough to the clutch to grab and then press the clutch for a second to let the engine come back to life (using it like the starter works)?

[doclees]

Originally Posted by vskid3

When you bump start it, are you just lifting your foot off the clutch or do you lift it enough to the clutch to grab and then press the clutch for a second to let the engine come back to life (using it like the starter works)?

I would let the clutch out smooth and fully engage. Never needed to re-disengage a clutch in the past with other cars. If I get a chance I will try the IACV disconnect today. Winter sucks, cold sucks.