Poor cold idle

[DevoBuzz]

I am running a 1 wire O2 sensor with the 86 GLHS II cal. The car will idle fine once in when warmed up in closed loop. It just stumbles and dies when cold. Would a 4 wire O2 sensor help this situation or is this a function of the cal?

Thanks,
Ralph

[PunKid]

I dont think its the O2 sensor. If the computer is seeing that then engine is not up to operating temp then it should be in open loop and therefore not looking at the O2 sensor.

Unless your thinking that the computer has switched into closed loop but the unheated one wire O2 is not reading well because it might be in fact be cold. I still doubt a heated O2 would change much

[turbovanman²]

Ox sensor is ignored on a cold start. I would look at items related to the cold, IE coolant sensor, IAT sensor etc.

What do you mean it dies? IE you start it, idles then dies, or it runs like crap and dies but all times, it will restart? or dies while driving?

[DevoBuzz]

To keep it running I have to give it gas. If I let my foot off of it, it will idle at 1000 rpm (too low for a cold engine) and start to stumble and sooner or later stall. I need to let it watrm up for about 5 mins and all is good. If I try to drive it while it still is cold, it will stall. It was fine before the T2 conversion.

I thought maybe thre 4 wire O2 would warm up quicker so I would only have to warm for a minute or so.

Could it be the Throttle Body / AIS?

[RoadWarrior222]

If you clear the SMEC and it still does it, then I doubt it's a sensor problem, since it won't be relying on anything it learned to "help" cold running. AIS is worth checking.

---------- Post added at 07:22 PM ---------- Previous post was at 07:20 PM ----------

BTW it's not running on last years summer gas is it? Just checking, even if it's not "stale" or had stabiliser in it, the morning start temps aren't conducive to happy running with summer gas yet.

[DevoBuzz]

No - the gas is fresh. I'll pop in a new coolant sensor and see if it helps. I have a feeling it is the AIS though. btw I'm running +20's if that makes a difference.

[RoadWarrior222]

Only way the coolant sensor could be doing it is if it's shorted (unlikely) and is telling the motor it's hot as soon as you turn on. Unplugging the coolant sensor is the usual way to force open loop running, so if it's failed to higher resistance or broke the circuit it still shouldn't be affecting cold running.

[shackwrrr]

No - the gas is fresh. I'll pop in a new coolant sensor and see if it helps. I have a feeling it is the AIS though. btw I'm running +20's if that makes a difference.

+20s on stock cal?

If so that is your problem. Before it warms up it pulses the injectors according to the ECM thinking there are stock injectors there and thus you get way too much fuel at cold start.

My cold start is crappy with only a 5 psi rise in base pressure so I can see where +20s would kill cold start drivability

[DevoBuzz]

+20s on stock cal?

If so that is your problem. Before it warms up it pulses the injectors according to the ECM thinking there are stock injectors there and thus you get way too much fuel at cold start.

My cold start is crappy with only a 5 psi rise in base pressure so I can see where +20s would kill cold start drivability

Yeah it is the stock 86 GLHS II cal. So then would a 4 wire O2 get the ECM off of the stock cal tables and into open loop quicker or is that more of a function of engine temp?

[shackwrrr]

Im not sure with the LM but my sbec as soon as the cold start loop is finished (60 sec) the computer starts using the O2 sensor. So I think if you had the 4 wire it would be a little bit faster.

[turbovanman²]

Its not an ox sensor issue, you can wire up the heated one if you want but its not really the problem. Try taking out some fuel pressure and open up the throttle blade via the adjustment screw.

[RoadWarrior222]

Or advance cam a tad if you've got an adjustable pulley and it's not dialled in yet.

[DevoBuzz]

No adjustable pulley. But I did open the TB a little like you said Simon. It seems better now - I set it to 1200 rpm at cold idle. After a few minutes it did start to stumble again but that could be because it was loading up with fuel. I blipped the throttle to clear it out and it seemed fine again. I'll see how it pans out.

Thanks for all the ideas guys!

Update: It seems now that the logic mod has trouble controlling idle speed. It's high and all over the place. We'll see if it settles out.

[turbovanman²]

No adjustable pulley. But I did open the TB a little like you said Simon. It seems better now - I set it to 1200 rpm at cold idle. After a few minutes it did start to stumble again but that could be because it was loading up with fuel. I blipped the throttle to clear it out and it seemed fine again. I'll see how it pans out.

Thanks for all the ideas guys!

Update: It seems now that the logic mod has trouble controlling idle speed. It's high and all over the place. We'll see if it settles out.

You don't want to open it too much, then the computer can't control it anymore as the idle motor is maxed out.

[shackwrrr]

Its not an ox sensor issue, you can wire up the heated one if you want but its not really the problem. Try taking out some fuel pressure and open up the throttle blade via the adjustment screw.

since it runs fine in closed loop, he only asked if the heated sensor would control mixture faster. Cold start will still suck.

[RoadWarrior222]

May help, as may using the block heater if it's got one, a +20 cal would help more.

[John B]

Was this problem ever solved?