1984 3.2 Carrera surging idle when cold

[p911dad]

Now that we have had a few cold days(32 degrees at 7am) my Carrera developed a little surging idle when cold, rising and falling about 600 rpm, from 800 to 1400 or so. Here is the really weird part: Steve Wong replaced the chip gratis about 2 years ago, no problem since(thanks for the great service, Steve!!). Today it started doing it again when ice cold, but only when an electrical device is on, ie, either the headlights or the radio or the AC. Turn off the lights or radio or AC(meaning all are off), and the idle returns to a steady normal 800 rpm. Can anyone offer a clue as to what is going on and why now? Thanks, Glenn

[ZOA NOM]

Time to do the "surge search" and then start eliminating issues like vacuum leaks, CO mixture, etc. I have found that most of the time, the CO mixture setting was the culprit. At the very least, it pays to establish that this setting is correct before chasing other more expensive possibilities.

[p911dad]

thanks, Zoanas. I have been through this before, and went through the engine and vacuum and idle switch, and etc. before. The last time swapping the chip cured it. This time it seems to be related to some subtle voltage or load change caused by adding an electrical load on the system- take it away and all is normal.. turn on an accessory and it starts to surge. it only lasts until the temp is off the bottom peg, then it totally clears. a puzzler.

[ZOA NOM]

If you suspect voltage, I would confirm the entire charging system and battery, especially all the grounds. Also, I have experienced a problem with the Air Flow Meter in which the surface of the potentiometer inside it was etched through the resistive material, causing very erratic idle. There is a method of fixing this by slightly moving the wiper arm to a new section of the wafer to allow it to run on a better track, which provides a smoother voltage representation output from the AFM. I would still recommend confirming the CO measurement, though. This would be consistent with the recent change in barometer.

[Rockafella]

Try this: when the car is idling and surging, tap on the idle control valve. If it cleans up, then you know to replace the valve. My surge went away when I cleaned this out with some PB blaster and carb cleaner, so I got away with not changing it.

I noticed that with the SW chip, it hiked the idle, so this might have masked a slowly dying/sticking ICV. Also, if your car is low mileage like mine was, it is more likely to have odd sticking pieces

[DRACO A5OG]

Originally Posted by Rockafella

Try this: when the car is idling and surging, tap on the idle control valve. If it cleans up, then you know to replace the valve. My surge went away when I cleaned this out with some PB blaster and carb cleaner, so I got away with not changing it.

I can atest to this, tapping the ICV with a screw driver cleared up the hunting immediately. My cleaning attempt failed and made it worse, more hunting but I could elliminate it by reveing it.

Metered it and it failed so I replaced it with a new properly reading OHMs ICV.

Thanks Rockafella!

[DonMo]

This came from one of Loren's rare helpful moments:


I cut some of the extra and here is a pretty useful series of steps to take.

1. Eliminate the idle valve as a problem by simply disconnecting it
when the engine is initially started. The idle should be very low and NOT hunt
if it's the problem. Then check that the idle switch is initially closed at
startup.
2. To check for a bad temp sensor ( most likely not the case here) just
disconnect the temp sensor and replace it with a paperclip.
3. An intake air leak (that which bypasses the AFM) will cause a lean
mixture and will not cause hunting but an idle-miss.
4. Make sure that the AFM is not sticking, i.e. the "flappy" is moving
freely when cold.
5. Make the fuel pressure is 35-38 psi at cold startup.

At least I thought it was clear and usefull.

[p911dad]

Thanks, I went though it again, sprayed ether in the likely junctions in the intake tract, shot brakleen in the idle valve, checked the temp sensor, etc. I went over the ground points again, and last year replaced the alternator and battery. When it is cold, which is a lot now that fall is here, and you switch on the radio , fan, headlights, rear defogger it goes into hunting mode. It is not a big thing because in a mile or two it goes away, it is just annoying to sit at a light and have the engine rise and fall by a 1000 rpm. In about two weeks I will put the cover on it and think about it in the spring(if indeed we ever get winter around here. All the oak trees still have all their leaves-veeerrry weird)

[scottb]

When was the last time you had your mixture checked? I had a surging/hunting problem, and a mixture adjustment cured it.

Scott

[DRACO A5OG]

Originally Posted by gmeteer

Thanks, I went though it again, sprayed ether in the likely junctions in the intake tract, shot brakleen in the idle valve, checked the temp sensor, etc. I went over the ground points again, and last year replaced the alternator and battery. When it is cold, which is a lot now that fall is here, and you switch on the radio , fan, headlights, rear defogger it goes into hunting mode. It is not a big thing because in a mile or two it goes away, it is just annoying to sit at a light and have the engine rise and fall by a 1000 rpm. In about two weeks I will put the cover on it and think about it in the spring(if indeed we ever get winter around here. All the oak trees still have all their leaves-veeerrry weird)

Try tapping on the ICV when it hunts, if it goes away, meter it, if it fails?

You need to replace it. Spraying Ether or Cleaning it does not fix the electronic component inside it.

Since I replaced my ICV, my baby now actually cold idles at 1200 RPMs and settles down gently to 800 RPMs after about 30 seconds on it's own. I never knew it did that or was supposed to until recently and also read it was supposed to do that originally. Very Happy Now