Cold Start Problem-no fast idle

spiderseeker · Dec 29, 2005

Wolftalk- I said 2500rpm based upon what others have posted as fast idle, in any event, it should be significantly faster than 1000rpm during cold idle.
I would much prefer 1500-1800 cold idle.
Steve

mike · Dec 29, 2005

Yes 1500-1800 is an appropiate fast idle, and that too is what I seek rather than the 500-800 "fast idle" warm up I currently have!!

spiderseeker · Dec 31, 2005

I made the mistake of changing 2 things at once, so I don't know for sure which helped. Attached are 3 photos- 1 before changes(notice tie-wrap holding rear of accordion air hose!- it was ripped under the tie wrap), the second photo(with new stencil, new straps for air hose- and rip fixed with black silicone glue). The third is of the TPS. The 2 changes were #1. fixing a tear in the rear of the accordion air intake hose that attaches to the airbox(I don't think this should matter since it's drawing in outside air anyway) and #2 was testing and re-installing the TPS(throttle position switch). I think the throttle position switch was NOT in the idle position. I tested the switch and it was fine. When I re-installed it, I had to rotate it full counterclockwise to get the "Click" for the idle position. I don't recall hearing the click when I removed it. As to the results of these 2 changes- the idle speed is now about 1200rpm at cold idle and smoother. Still a few hundred rpm low but MUCH better. It's probably drivable now when cold , before it wasn't. I'm still checking a few things and I'll be adjust the mixture soon, that may be all that's left. The reason that I think it was the TPS, is that the TPS sends "idle position" to the ECU, otherwise the ECU thinks the car is being driven at some higher rpm and adjusts the mixture accordingly, just an uneducated guess.(still a rookie at this).
Here's wishing everyone a fast idle when cold in the New year !
Steve
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wolftalk · Jan 4, 2006

hi steve,

any air leak into the plenum is bad news. Tom equated the AAV to a controlled vacuum leak, but there's one huge difference. Air bypassing the throttle plate through the AAV is still being measured by the metering plate in the air box, so the fuel mixture is adjusted appropriately.

if you have air sucking directly into the intake, the metering plate won't see it and the mixture will be too lean. Once the lambda stuff kicks in, the frequency valve will be fiddled with to compensate, but you're screwed in open loop operation.

before adjusting the mixture, stick the scope back on and see if the duty cycle is closer to 50% in closed loop. The base mixture setting may be fine when there's no leaks. Plus, see what the duty cycle is in open loop (ok, just to appease my curiosity...not sure it if should be 50% or 60% )

happy new year!

phil

spiderseeker · Jan 4, 2006

wolftalk- I'm not sure it can be considered an air leak, since it was leaking at the air input area before the airbox (rear of accordion air hose). I don't think that would affect anything.
I do need to try the scope again, I also have a "duty cycle" meter coming any day now.
Not sure what a 50% duty cycle should look like on the scope.(never used it for that before). Must be somewhat like a squarewave I think.
The main thing is that it's FIXED. The car starts and runs great , hot or cold now. The idle is just a little low for fast idle(1200rpm), which I actually prefer.
I also know that the pulse air injection electrovalve is bad(open coil). I'm trying to locate one now.
Steve

Mark 328 · Jan 4, 2006

Steve:
FYI, there is a TPS on listed on ebay.

Mark

spiderseeker · Jan 4, 2006

Mark- my TPS was just out of adjustment, it's the "pulse air injection electrovalve" that I need.
Steve

wolftalk · Jan 5, 2006

hi steve,

the air flow metering is done by the big plate right beneath the black air filter box. Assuming the accordian hose you referred to was the one between the throttle body and the fuel distributor "air box" (probably me using the wrong term), then a leak in that hose would be unmetered air into the plenum.

anyway, I'll stop flogging that dead horse and say something useful

I got a used electrovalve from GT car parts in arizona. 623-780-2200.
T. Rutlands/maranello auto parts usually have parts cars laying around as well.

Since you'd proven the electrovalve coil is open, you may want to see if you can expose the coil wire by removing the wrapping. Sometimes the wire broke/fused within a few turns of the lug, and you can toss the short segment and reattach the remaining end. A few turns of wire won't matter.

With enough time and scotch, you can even rewind the coil yourself if you can dig up the right gauge coil wire...but I can't recommend it unless you are desperate...or have full bottle of scotch.

wrt duty cycle, yup, a 50% duty cycle would look like a perfect square wave. Duty cycle is defined as the ratio of:
(time on) / (time on + time off)

spiderseeker · Jan 5, 2006

wolftalk- the attached photo shows the accordion hose that I was referring to.(pass side air intake area is where the rip was in the accordion hose) The only difference I can see would be that hot engine air was entering the system instead of cold outside air, so I don't think that was the problem.
Thanks for the source for the electrovalve, I guess I'm not the only one that had one go bad. I may check the windings, if I can figure out how to get to the coil, it's attached to the vacuum valve rather securely.
I've never seen anyone show the duty cycle as a squarewave on a scope, I'd like to see that.
Steve
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