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Discussion Starter #1
Been fighting this for a while....
My 84 Spider with 72K miles runs great but has a bit of a rough idle and a bit of surging back and forth between 800 and 1100 rpm (indicated).

Background:
all fuel and vacuum hoses (silicon) have been replaced. New plugs, wide bosch rotor and cap. injectors cleaned a few years ago by Greg Gordon's shop.

I've looked for vacuum leaks, using the compressor attached to the oil dipstick method. I found a few small leaks and was very disappointed when their repair did not result in any difference in idle.

There's lots of other items that have been replaced over the years (fuel filters, fuel pressure regulator). AOS has been cleaned out. AAV replaced with manual valve.


A couple of quick questions..
1. My TPS works correctly when checked with my meter. I know this should eliminate the O2 sensor out of the idle equation. When idling, if I disconnect the TPS, idle rises by a few hundred RPM (and of course seems smoother, but still not right). Is this behavior normal or is it telling me something that I'm missing?

2. I have not checked the voltage output from my O2 sensor at idle as, again. it shouldn't be part of the equation. If I disconnect the O2 sensor while at idle, I sense no differences, which is what I expect. Is my assumption correct?


What am I missing? I've tried three different sets of new plugs (different brands) and experienced no difference in idle.

I remember years ago, that Loge plugs always seemed to provide a smoother idle. Its been many years since I've had them in the car but wonder if it might be worth going back to them. I'm currently running NGK iridium gapped at .030.

Any suggestions are appreciated!
 

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AOS has been cleaned out.
Do you mean the Oil Vapor separator?

When idling, if I disconnect the TPS, idle rises by a few hundred RPM (and of course seems smoother, but still not right). Is this behavior normal or is it telling me something that I'm missing?
Is the TPS adjusted correctly? And also the throttle butterfly? The idle stop for the butterfly is adjustable but it is not meant to be adjusted - rather set and left alone. Since many have been messed with this is what I do: Back off the idle stop screw until the butterfly is completely closed then turn it in until it is just barely touching the butterfly's stop. I like to set it so the butterfly opening is about 25-50 rpm over completely closed. Make the final idle speed adjustment with the idle speed adjuster (on the plenum).

Now position the TPS so the switch will tell the computer the throttle is at idle.

If I disconnect the O2 sensor while at idle, I sense no differences, which is what I expect. Is my assumption correct?
The unheated O2 sensor will not be hot enough to function at idle so what you report is what I'd expect.

Has the AFM been messed with? The flap in the AFM has to 'float' smoothly on the incoming air. 'Back in the day' it was common for folks to loosen the spring tension on the flap thinking it would provide more fuel & power. It did not but it did mess up the AFM's signal to the computer. At idle the air flow is obviously the least so if the spring tension is too loose then the flap will oscillate instead of floating smoothly.
 

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Does it do it when you first start the car up, also?
If you've checked out all the other things, you should check the coolant temp sensors and the thermotime switch.
 

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Discussion Starter #6
Thanks for the replies.

I had NGK's set at .025 previous to this set.

During cold start, the car idled higher but still not smooth. After warm up, similar symptoms but seem worse (rougher) as the car is idling lower.

It's been years since I checked the cold start sensors. Given that they're original, I'll check them and report back.
 

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Discussion Starter #7
Do you mean the Oil Vapor separator?



Is the TPS adjusted correctly? And also the throttle butterfly? The idle stop for the butterfly is adjustable but it is not meant to be adjusted - rather set and left alone. Since many have been messed with this is what I do: Back off the idle stop screw until the butterfly is completely closed then turn it in until it is just barely touching the butterfly's stop. I like to set it so the butterfly opening is about 25-50 rpm over completely closed. Make the final idle speed adjustment with the idle speed adjuster (on the plenum).

Now position the TPS so the switch will tell the computer the throttle is at idle.



The unheated O2 sensor will not be hot enough to function at idle so what you report is what I'd expect.

Has the AFM been messed with? The flap in the AFM has to 'float' smoothly on the incoming air. 'Back in the day' it was common for folks to loosen the spring tension on the flap thinking it would provide more fuel & power. It did not but it did mess up the AFM's signal to the computer. At idle the air flow is obviously the least so if the spring tension is too loose then the flap will oscillate instead of floating smoothly.
Sorry I didn't see the rest of your input earlier....
The throttle stop has not been messed with to my knowledge.
The AFM is original and shows no sign of ever being opened.

The history of this car is that my brother purchased it in the spring of 1986 from a Tampa Mercedes dealership where it had been traded. The car was one owner and had 15K miles on it when my brother bought it. I purchased it from him in 1993 with 43K miles. The L-jet system is stock. None of the sensors (other than O2 ) have been changed. The cold start injector is not original as I replaced it about 6 or 7 years ago.

BTW, all manifold vacuum hoses are connected to their correct ports as are the OVS. I have checked for vacuum leaks everywhere I can think of, including under the package shelf at the vacuum sensor.
 

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When the idle revs like that, up and down...that sounds so much like a bad o2 sensor. Especially if it doesn't do it during warm up, when the LJet is running open loop, cutting out the o2 sensor readingss.

How does it start when cold or warm? Any troubles?
 

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It sounds like you've already checked & ruled out the 'usual suspects'. If the TPS is correctly adjusted for idle position then the O2 sensor should not come into play as the computer ignores the O2 sensor at idle.

There is an idle CO adjustment on the AFM. I don't think that if misadjusted it would adversely affect the idle character significantly but it doesn't cost anything to try adjusting it. Keep track of how much/which way you move the adjuster so you can return it to the starting point.

Finally, the contact strip inside the AFM can become worn. There is a way to adjust the position of the wiper arm to move the contact nubs to an unworn section of the contact strip. Have you tried a known-good AFM to see if that makes any difference? I think I have one that I am keeping as a spare but if you want to try it and are willing to pay the postage you can borrow it.
 

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And distributor bushings. For whatever reason, Bosch injected Spider "distributors" seem not to get enough lube to the shaft, can become very sloppy. On mine, it got so bad the rotor hit and tore up the cap.
Andrew
 

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Another item, this happened on mine. If you restrict the idle air too much, the idle speed drops to the point where the ECU says uh-oh and advances the spark, in an effort to bring the idle up. I wonder if you're in that never never land?

Andrew
 

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Discussion Starter #14 (Edited)
Thanks for the replies....

1. Spark plug wires are good. I have swapped wires with others during troubleshooting with no change.

2. I had RJ cams, (street cams for L-jet) installed a few years back. I took the head to RJ (burned exhaust valve) and he set the valve clearances for me. I have checked cam timing since this started and I feel I'm dead on the cam.

3. I'll double check distributor for play.

4. My car starts pretty easy, cold or hot. No long cranking or having to manipulate the gas pedal (maybe a little, sometimes).

5. To follow up, I took cold reading of the CTS and TTS last night. Ambient temp was about 70F.
CTS- 2,400 ohms

TTS
G to GND 36.4 ohms
W to GND 1.9 ohms
G to W 36.4

I'll get warm reading later today.

I do think I'll do compression testing as well, along with checking fuel pressure.
 

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Compression is probably a long shot, but still, if one is low, that'll make a difference.
And it ran OK before with these cams? That is, the L Jet was happy with these cams?
Andrew
 

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Couldn't he just disconnect the electrical connector at the AFM to quickly determine if the ECU, TPS, O2 Sensor and AFM are negatively interacting at idle?
 

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Discussion Starter #17
Car ran fine with the cams .

If I disconnect connector at AFM, car starts (hard) and dies.

CTS with car at operating temp
385 Ohms.

TTS
G-Gnd 72 Ohms
W- Gnd 143
G-W 72

Both look like they're good to go.
 

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Remember, there are two CTS's. One for the FI, one for the ECU. Around cyl #2 is the one not many people mention. It's actually the same sensor type as the other one and interchangeable.
 

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When I got mine back together after having the injectors cleaned, it ran like crap. I finally took it for a drive, nursing it at intersections. On the freeway it finally cleared up, and power came back! I waited way too long to install the injectors after having them cleaned, and a couple were sticking...

Maybe you can clear things up with an Italian tune up :wink2:
 
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