[Diy_efi] Dead cold rough idle

Fri Feb 17 21:39:02 UTC 2006

After going to the Holley throttle body and edelbrock intake, I lost the warming of the TBI that is normally there with the stock intake.  This caused a rough idle between 5 and 10 minutes into the runtime cold.  You can physically see the icing around the edges of the throttle bores and plates. Mine would actually get so bad, it would stall out.  I had to purchase a TBI to carb intake adapter plate that was heated by coolant.  Holley makes this unit for this exact reason.  If you are using a factory intake and non-modified TBI, this shouldn't be too much of a problem, but it still exists.  Another thing is to make sure you use an enclosed air cleaner during the cold months,  one that still has the stovepipe that hooks to the exhaust manifold.  Get some warmer air up to the TBI.  An open element air filter makes everything worse when it is colder.

Andy
82 Z28 Camaro built 355
87 Z24 Cavalier 2.8 stock
90 Lumina 3.1 stock
93 Fullsize Blazer custom built Vortec Holley TBI
http://www.bds-suspension.com/pride_joy151.html

  ----- Original Message ----- 
  From: Lee M. Lemoine 
  To: diy_efi at diy-efi.org 
  Sent: Friday, February 17, 2006 3:40 PM
  Subject: Re: [Diy_efi] Dead cold rough idle

  I guess thats also possible..  it seems to be odd that it idles up fine, but then after the cold start enrich decays off, it starts this problem.. 

  On 2/17/06, Rick McLeod <dunvegan at sbcglobal.net> wrote:
    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
    > >
    > >
    > >
    > >
    > >
    > >
    > _______________________________________________
    > >     Diy_efi mailing list 
    > >     Diy_efi at diy-efi.org
    > <mailto:Diy_efi at diy-efi.org>
    > >
    > http://lists.diy-efi.org/mailman/listinfo/diy_efi
    > >
    > >
    > >
    > >
    > >
    > >
    > > --
    > > 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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  -- 
  Sincerely,

  Lee M. Lemoine 
  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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