Engine hunting

[Enoch]

Ho Peeps, I have a weird scenario with my 2.0 dohc I4. It ran out of fuel tonight so I put some more in - fresh fuel straight from the pump. When I restarted it (it was cold at the time) it ticked over at about 1000 rpm - previously it was ticking over at about 800. After a minute or so it started hunting eg revving to about 2K then falling back to 1k before revving back up again. I turned it off after a few seconds of this - I don't have the rad connected yet so don't want to push my luck. If I open the throttle it seems to be ok but just does not want to tick over properly. Anyone got any ideas?
I just knew it was too good to be true

[deezee]

Idle control valve or temp sensor fault.

[Enoch]

Interesting. So if there was no water in it and as a result the water temp sensor was reading low that could do it? The stat housing was cold and the head hot at the time. If it had been full of water I am guessing the water temp and engine temp would be much closer together?
I will see what it does when it has cooled right down, it will have to be tomorrow now I guess.

[deezee]

What engine management are you using? The one that came off the Sierra? If your coolant isn't touching the temp sender, or the temp sender has failed, its most likely running rich (choke) as its trying to warm the engine up. Is your a catalytic model?

Also if the idle control valve is sticking usually means it will rev up to 1250 ish and back down to 800 ish. Check for air leaks, The idle control may be fine, but your TPS might have been moved.

[spud69]

It hasn't got trapped air in the line or pump has it Dave. Might be worth letting it pump to an open end for a while.

Just 2p worth.....AndyH

[Enoch]

Hi Folks, I have found a bad earth but have not had time to deal with it yet. I am sure it is running rich due to the thermostat housing ( and therefore the temp sensor) being cold compared to the engine. I will fix the earth and then sort out my cooling system before trying again. Thanks for the pointers, I have not really got involved in injection before. Just for the record it's an EEC IV without cat.
Cheers!

[Enoch]

Ok, this is getting weird now. I remade the earth and started it from cold, now it revs to just under 2k and sits there. If I disconnect the idle speed control valve the tick over speed does not change. I have buzzed out the wires to it, they are fine. before it ran out of fuel it was perfect, it has not run properly since.

Just as a sanity check let me run this by you. When the fuel ran out it spat back quite violently- I think I saw a blue flash somewhere round the inlet manifold. Could it be that the backfire has taken out the inlet gasket and I now have an air leak? I don't want to take the manifold off if it's a completely stupid idea but something changed at the point I got that backfire - it has not ticked over properly since. The gasket is actually that instant stuff, I could not find a proper gasket for it, I am hoping I don't have to scrape it all off.

Can someone tell me if I am completely barking mad or not?
Would an air leak cause a high / erratic tick over?
Thanks in advance

[twinturbo]

Ahh... When you tell all the facts.

Yes an air leak will cause an erratic idle, by the sounds you have blown off a pipe fitting or as you think maybe the gasket has failed.


The Common culprit is that back breather hose.


TT

[Cyberbeej]

i'll go with the gasket, always fit the right part the right way first time round or you always end up doing it in the long run.

[twinturbo]

Or fit one that's better than the right part

TT