[Diy_efi] Dead cold rough idle

Fri Feb 17 19:07:42 UTC 2006

Icing is a good potential, a lot of throttle bodies
have a pre-heat of some kind, the TPI on GM
Camaro/Vette 85-92 era had a water line that was sort
of the bypas hose circuit, many folks (myself
included) have passed a copper pipe under the Throttle
Body for summer use, and just move the hose from the
Body to the pipe and back every fall/spring. That way
you get the de-icer in the winter and not in summer.

just an idea, my memories of my old VW icing up at
idle even after engine warmed up, usually forgotten to
unlock the air diverters for carb intake preheat from
summer mode, It was a simple solution but extremely
elegant in function. You may never see frost or icing,
it may be occuring inside the passages, but will wreak
havoc with idle if it is occuring.

Good luck!

--- Torbj?rn Forsman <torbjorn.forsman at gengas.nu>
wrote:

> Hunting at idle might also be caused by wrong
> control parameters for the 
>   idle speed stabilization or too early ignition
> (then the engine 
> response to a change of the idle air valve will not
> match the control 
> parameters and the system will oscillate).
> 
> Idling problems at a cold engine can usually be
> avoided by a good intake 
> air preheating and, of course, heating of the intake
> manifold. Some 
> european TBI engines (for example, the 1,6 and 1,8 l
> engines of VW 
> Golf/Rabbit from about 1988 to 1997, with Bosch
> Mono-jetronic or 
> Mono-motronic TBI) have an electric PTC heater of
> about 300 W directly 
> below the TBI unit. This heater is controlled either
> by a thermostat or 
> by the ECU, so that it is switched on from a cold
> start and until the 
> coolant temperature has reached about 50-70 ?C
> (120-160 ?F).
> 
> Best regards
> 
> Torbj?rn Forsman
> 
> Lee M. Lemoine wrote:
> > Usually when the engines hunting like that your at
> the edge of a fuel 
> > map... meaning that either your 500 rpm table is
> set too rich, so the 
> > extra fuel makes the engine rev a slight bit...
> but the 1000 rpm table 
> > may be too lean, so it falls back again... 
> (rinse, repeat, etc) and 
> > viola -- a rough idle.   The other things that
> I've seen related to this 
> > would be the air intake temp compensation (too
> much / too little) or 
> > even coolant temp compensation, although you say
> it seems to do that 
> > even after warmup.
> > 
> > Most EFI systems use a 'cold start enrich' map,
> which lasts the first 30 
> > seconds or so, and fades out gradually.  What this
> means on a cold 
> > engine is an increased amount of fuel -- causing
> it to start easier and 
> > (in your case) idle smoother..  my guess is that
> whatever range your 
> > trucks idling in'...  the fuel maps too lean ... 
> > 
> > Related to that ...  When's the last time you
> changed the fuel filter / 
> > how's your rail pressure?  Maybe your fuel pump is
> also weak at colder 
> > temps?  (just a thought!)
> > 
> > --Lee
> > 
> > 
> > On 2/17/06, *David M. Ingebretsen*
> <dingebre at 3dphysics.net 
> > <mailto:dingebre at 3dphysics.net>> wrote:
> > 
> >      
> >     Hello all. Been awhile since I've lurked here.
> >      
> >     Setup: 1990 Jeep Wrangler, 4.2 liter inline 6,
> Originally a Howell
> >     GM TBI conversion with 1227747 ECM, now
> happily modified and tuned.
> >      
> >     I've searched the archives, web, and FTP site
> and didn't find
> >     anything which helped.
> >      
> >     The problem is this. When cold, (even using
> the Howell supplied bin
> >     and their "cold" bin) at or near 0 C, the Jeep
> starts great, starts
> >     idling fine but after some 15 to 20 seconds at
> idle, the RPM's drop
> >     and it begins to idle very rough. When I drop
> it into gear (was
> >     manual, now Chevy 700R4 auto, yes I added a
> pk/ntrl switch and have
> >     verified its operation with WinALDL, and I am
> using the ECM to
> >     control TCC lockup) and go, it runs fine.
> Smooth engine speed and
> >     running. But soon after I stop (2 to 3
> seconds) it starts to idle
> >     rough, sputter, cough, on occasion die. If I
> poke the accelerator it
> >     comes back and when I start, no problem. When
> fully warm, no
> >     problem. When I start it at about 30 to 50 C,
> no problem. This was
> >     the same with the manual.
> >      
> >     Question is what -exactly- controls the cold
> open loop -idle- AFR?
> >     I've had no luck changing the O/L AFR table
> except to make it run
> >     crappy before it goes into closed loop. I've
> adjusted the closed
> >     loop temp threshold, cold and warm choke
> timer, choke table, cold
> >     AFR v. MAP, time out decay mult. V. Cool. O/L
> idle AFR enable time
> >     delay, O/L idle AFR time delay, closed loop
> timer warm threshold and
> >     timer. I've looked at the Accel Pump v.
> Coolant but that doesn't
> >     seem to be a problem because I can hit the
> throttle and it snaps
> >     right in. I've searched the AZDZ hack to see
> if I could glean
> >     anything, but didn't find anything useful.
> >      
> >     Like I said, it is fine when it starts
> warmish, but when it is dead
> >     cold it struggles. So, my thoughts turn to the
> choke table, but I'm
> >     not sure.
> >      
> >     Any ideas?
> >      
> >     Thanks all.
> >      
> >     David M. Ingebretsen M.S., M.E.
> >     Collision Forensics & Engineering, Inc.
> >     2469 East Fort Union Boulevard, Suite #114
> >     Salt Lake City, UT 84121
> >      
> >     dingebre at 3dphysics.net
> <mailto:dingebre at 3dphysics.net>
> >     Work: 801 733-5458
> > 
> >     	
> >     	
> > 
> > 
> >    
> _______________________________________________
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> >    
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> > 
> > 
> > 
> > 
> > 
> > 
> > -- 
> > Sincerely,
> > 
> > Lee M. Lemoine
> > http://www.turbochargedsoul.com/
> <http://www.turbochargedsoul.com/>
> > '06 Subaru Legacy GT Limited - 250/250 AWD 5EAT
> > '93 Chevy Cavalier Z24 Convertible - 300/330 FWD
> 5MT (Mclaren Turbo!)
> > 
> > 
> >
>
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