Faulty Idle Air Valve? - Alfa Romeo Bulletin Board & Forums
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post #1 of 33 (permalink) Old 02-17-2012, 07:34 AM Thread Starter
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Faulty Idle Air Valve?

In this video I am holding a high idle with the pedal, idle is usually around 850-900 RPM. However, when left at idle, the revs drop suddenly and would kill the car.

By holding the idle high in this video, you can see the erratic behavior of the revs suddenly dropping then returning.



My thought is idle air valve, any other suggestions?

Best,
HJM

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post #2 of 33 (permalink) Old 02-17-2012, 07:53 AM
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Air leak is more likely. At idle the ECU goes to a lean idle fuel air mix, not controlled by the O2 sensor. Extra air can kill the engine but once the throttle is cracked the ECU can fix small air leaks by enriching the mixture. Same symptoms when cold or warm? Then maybe the AIC is at fault. The AIC is pretty reliable.

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post #3 of 33 (permalink) Old 02-17-2012, 08:03 AM
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The IDLE air control valve really only comes into play at IDLE (hence the name). Pop the hood and look for air leaks, first off (unmetered air messes things all up). You getting a CEL code? Retrieve that too and tell us what code(s) you have. Holding the throttle opened kind of takes the idle control valve out of the picture for the most part. Check ALL your vacuum lines and follow the ones that go down into the left front fender as well, you will have to remove the inner fender liner to make sure they are all still connected down there as well. Could be may things, but check for false air first. Also, did you check the distributor yet?
Charles

-'91 164L 5 speed 222k miles and counting -'04 Volvo XC70 -'89 Volvo 244 "the Brick"

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post #4 of 33 (permalink) Old 02-17-2012, 10:18 AM
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That looks strange to me

I have never seen a tach response so rapid, normally the tach has some hysteresis in it; those tach changes were nearly instantaneous. I couldnt really hear the engine though. Makes me think electrical since theres no way the engine is dropping its true RPM that fast.

AFTER you check for tramp air, and assuming you find none, Is it possible you have a coil/plug wire/plug issue? What signal feeds the tach in that car?

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post #5 of 33 (permalink) Old 02-17-2012, 10:25 AM
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I'm hearing a true drop in RPM. These V6's rev pretty quick both up and down, IMHO.
Charles

-'91 164L 5 speed 222k miles and counting -'04 Volvo XC70 -'89 Volvo 244 "the Brick"
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post #6 of 33 (permalink) Old 02-17-2012, 10:29 AM
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OK fair enough

seems very square-wavish to me, easy enough to find leaks by using carb cleaner (not a HOT, just warm engine) on all vacuum lines, or an unlit butane torch. Check the dogbone / 'silent block' engine mounts. Also if you have a FP gauge put it on and check the pressure on the rail. All this can be done in 20 minutes tops.

If no leaks are found I would suspect ignition

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74 GTV with 10548's and Ingram pump --speedo been around at least twice -- [B]needs new oil rings[/B]!
1995 LS Q runners Auto Green/tan [B]230K[/B] 100% LCD paint absolutely SHOT!
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Misc parts laying around for 24V and 2Liter- always need more it seems
2004 Tacoma 4 door TRD (wifes car/kid hauler)- 172K
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post #7 of 33 (permalink) Old 02-28-2012, 01:02 PM Thread Starter
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Its getting worse...

I thought it was false air, the car would "buck" randomly at cruising speed, but nothing terrible.

Now it sounds as if the engine is missing, especially under load in a high gear at low RPM. I checked all vacuum lines, retighted and replaced some hoses, thinking I had found it, but no, same behavior. Now I am thinking ignition.

Going to try replacing the coil, spark plug wires are new, distributor rotor replaced less than 5k miles ago.

Any other ideas? Also will post a video of engine at true idle. The sudden drops are more apparent when it is colder out. It's been relatively warm in the northeast the past few days and i have not experienced the rough idle so much as the missing while driving.

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post #8 of 33 (permalink) Old 02-28-2012, 04:21 PM
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Have you check for error codes?

Red 1991 164S, Black 1991 164S, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
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post #9 of 33 (permalink) Old 02-28-2012, 04:30 PM
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Have you rechecked parts replaced only 5k ago? Never assume replaced parts are still A-OK.

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post #10 of 33 (permalink) Old 02-28-2012, 06:44 PM
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Can you isolate what cylinder is giving you trouble by either pulling injector connectors or plug wires? That would also give you idea if you have a bad injector or plug. Be careful pulling plug wire though for obvious reasons.

Reminds me of a story: An Alfa Spider zapped me good once poking around with plug wires many years ago when I had it on a test drive. It wasn't running well, but I think I found the bad wire causing the problem! I got back in the car rubbing my elbow and took it back. My girlfriend at the time was a big Alfa fan (you can see why I liked her) We didn't work out in the end (the Alfa or the girlfriend).
Charles

-'91 164L 5 speed 222k miles and counting -'04 Volvo XC70 -'89 Volvo 244 "the Brick"
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post #11 of 33 (permalink) Old 07-02-2012, 08:15 PM Thread Starter
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Bringing this thread back

SO I am revisiting this thread as I STILL cannot figure this one out on this particular car.

Still rough running, although the idle seems to have evened out quite a bit. The car sat for about 2 months and I recently dug back into it. My friend, (ex-Porsche/german car shop owner) helped me do some trouble shooting.

He said on the AFM for the L-jet system there was a little allen key that would manually adjust the lean/rich mixture AFTER the AFM and these were set at the factory and not to be changed. He pulled the plastic cover off it and adjusted it a bit to stabilize the idle.

We checked for air leaks with starting fluid/carb cleaner and there weren't any that were overly apparent. Took the car for a ride and it felt like it was running on 5 cylinders or missing. Not the free-revving, smooth engine I am used to.

Here's what I did today to try to trace down what's wrong:

1)Pulled plug wires to check/isolate bad cylinder. This garnered nothing, still rough running, some wires didn't even make that much of a difference when pulled, but nothing overly apparent.

2) Checked injectors by listening with stethoscope, all injectors are clicking normally.

3) Pull spark plugs to see if one was wet. All looked dry and fine.
4) Did compression test on all cylinders. Got the following pressures:
1-160PSI
2-145PSI
3-150PSI
4-150PSI
5-145PSI
6-150PSI

5) Checked valve timing for perhaps a skipped tooth on T-belt. With crank aligned and at TDC, alignment marks on cam hubs line up with 69/72.5 Deg diagram. Timing checks out.

6) Checked temp sensor. Engine was hot, got a reading of .6kOhms, engine cooled down a bit (still sitting in 80 degree weather, probably internal temp around 100-110F) and resistance rose to over 1kOhm. I believe this works, and should read between 2-3kOhm at 60F?

7) Checked wires at temp sensor plug. Intact and making good contact under rubber boot.

8) Checked Coil by replacing with known good. Made no difference.

9) Checked spark at all wires and coming from coil.

10) Checked throttle position sensor, verifying no resistance across 2-18 at closed and infinite resistance across 18-3, and vice versa at full throttle.

SO WHAT ELSE? Put it all back together and still running rough. Sounds like it's missing, mis-firing, etc.

OH YEAH: Checked fuel pressure at rail right out of supply line. Fuel pressure was 45PSI solid. My Porsche friend said this was too high for an L-jet system (he continued to pull out his Bosch service manual and show me it should be around 35PSI). Does too high fuel pressure have a terrible effect on the performance? Should it really be at 35PSI, meaning my fuel pressure regulator is bad? I checked for fuel in the vacuum line from the FPR to the plenum, and didn't find anything overwhelming. Looked dry to me.

Anyone, please point me in the right direction...!

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post #12 of 33 (permalink) Old 07-02-2012, 08:48 PM
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So not only did your mechanic friend not help you find the real problem, but now he has screwed up the factory setting. Nice. The point of the pulling plugs while running exercise was to see which cylinders are not working, which you seemed to find. My guess is you have corrosion in a few of the fuel injector connectors. Most of these cars have broken injector connectors and no longer seal out moisture well at all. As these cars sit undriven, they develop corrosion in these connectors and do not fire the injectors well at all. Carefully inspect those. If you find greenish corrosion on the pins, than that is it. Causing weak injecting or even no fuel, in 1 or more cylinders. I had to replace all my injector connectors to make them all reliable again. Prior to that, I had constant battles getting the car to run on all 6 all the time in all conditions. Have not had any trouble ever since. Do not underestimate the need for a weather tight seal at all the fuel injector connectors. Your car is Motronic not L jet. Fuel pressure is supposed to be 42-47 psi. If you pinch the fuel return line, you get up to 58 psi.
Charles

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post #13 of 33 (permalink) Old 07-02-2012, 10:12 PM
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A Porsche guy trying to fix an Alfa...hahaha...good one LOL. Rather than pulling out the Bosch manual, you need the ALFA manual or CarDisc.

Red 1991 164S, Black 1991 164S, 1972 Berlina, 1973 Berlina rebuilding SPICA engine
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post #14 of 33 (permalink) Old 07-03-2012, 08:30 AM Thread Starter
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Why would the injectors be clicking regularly is the connectors were bad? I will pull them off and take a look today.

Any other thoughts? Bueller?

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post #15 of 33 (permalink) Old 07-03-2012, 09:01 AM
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ignition

plug or coil wires, plugs, rotor, cap etc would be my 'most likely suspects'.

goats

74 GTV with 10548's and Ingram pump --speedo been around at least twice -- [B]needs new oil rings[/B]!
1995 LS Q runners Auto Green/tan [B]230K[/B] 100% LCD paint absolutely SHOT!
1995 LS 5 speed Green /tan 48K Q runners squadra chip 100 % LCD -- nice tight car
Misc parts laying around for 24V and 2Liter- always need more it seems
2004 Tacoma 4 door TRD (wifes car/kid hauler)- 172K
Mission Vsi, Mission Mod 2, - 20+ years of hockey on these!
radio flyer- rusty from disuse!
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