High Idle

3670 Views 12 Replies 6 Participants Last post by 930cabman, Mar 9, 2015

930cabman

Discussion Starter · Mar 8, 2015

Our "Sandy spider" is running and not bad at that. It has been a long road but we are getting close. Hopefully when the 3' of snow melts, she will be ready for a test ride. There are still several issues, one of them is the idle speed. I do not have a working tach, but know the speed is too high. If the idle adjuster compresses the "O"ring the idle is still around 1200. All the vacuum hoses are new. I am at a loss.

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ghnl

· #2 · Mar 8, 2015

Is the vane inside the AAV closing? The AAV's vane is supposed to be open when cold to increase the cold idle speed. Then, as the engine warms up, the vane should close so the idle speed returns to normal. When the engine is running you can squash the hose to the AAV to block the passage of air. If the idle speed drops then the AAV is likely not closing.

If the Idle Adjuster's O-ring is old it may have taken a set and resist adjustment. A new O-ring is squishable so the ID can vary which is how the idle adjuster varies the idle speed.

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sloboy89

· #3 · Mar 8, 2015

930cabman said:
Our "Sandy spider" is running and not bad at that. It has been a long road but we are getting close. Hopefully when the 3' of snow melts, she will be ready for a test ride. There are still several issues, one of them is the idle speed. I do not have a working tach, but know the speed is too high. If the idle adjuster compresses the "O"ring the idle is still around 1200. All the vacuum hoses are new. I am at a loss.

There are a couple of issues here. First, is it cold there such that the AAV is working? This will affect the idle speed. After the car warms up, the idle speed will drop a bit.

Second, there is an idle-adjust screw where the throttle linkage attaches to the plenum. This screw adjusts the position of the plenum butterfly valve. Normally, you don't mess with this screw, but if the PO did, the valve may not be closing as far as it should and therefore idling too high.

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930cabman

Discussion Starter · #4 · Mar 8, 2015

We have two AAV's, neither one is functioning. I did plug the vacuum line exiting the AAV, so it is out of the loop.

The "O"ring is soft and does compress as it should.

The adjusting screw in the throttle body is set to hold the butterfly open a couple of thou.

Could the VVT somehow effect the idle speed?

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sloboy89

· #5 · Mar 8, 2015

930cabman said:
Could the VVT somehow effect the idle speed?

You should put the year of your Spider in your signature block, so that everyone knows what you are dealing with. I looked back at an earlier post, and it appears that your car is an '85, which should have an electronic VVT.

The VVT should not have any effect on the idle. When the throttle is opened full, the VVT solenoid extends a plunger, which in turn causes the intake cam to advance, providing increased power. If the VVT is inoperable, most likely the solenoid is not extended, and thus, it should have no effect on the idle.

If, somehow, the solenoid were stuck in the extended position such that the cam was advanced at idle, it might have an effect, but I think that the car would run rough and probably not at a higher idle.

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mcola

· #6 · Mar 8, 2015

sloboy89 said:
I think that the car would run rough and probably not at a higher idle.

Yes, it would idle very poorly as if running on 3 cylinders, and maybe an idle speed that would seem to be about 500rpm.

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mcola

· #7 · Mar 8, 2015

Is the TPS set properly? Eric, if its out of position and not telling the computer the engine is at idle, could this result in more fuel or faster idle speed?

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ghnl

· #8 · Mar 8, 2015

I don't think a mis-adjusted TPS would increase the idle speed. But it can cause it to be somewhat irregular. With the TPS adjusted so tha the computer knows the throttle is at idle, the computer then follows its pre-programmed idle mixture map. If the TPS is mis-adjusted & the computer doesn't know it's at idle, then the computer tries to use the O2 sensor's inputs to adjust the mixture. It can't do this very well at idle so the idle speed will vary.

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vf31rhill

· #9 · Mar 8, 2015

A very common cause of high idle is unregulated air entering the air induction system between the air flow meter on top of the air filter lid, and the aluminum intake manifold. In other words, the cross over rubber duct plus the cross over hard plastic piece. The accordion pleats on the cross over rubber duct will crack in the pleats and allow unregulated air to enter the air induction system. Remove both pieces and do a minute inspection of each part, with special attention to the accordion pleats. You can buy a new rubber cross over if needed from IAP (about $88). This was the problem I had and working with the air idle fiting on the intake would make zero differences in my high idle problem. I located a huge rip in the accordion and a new rubber cross over from IAP solved the problem. Also had side benifit of making the Alfa much easier to crank up when cold.

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930cabman

Discussion Starter · #10 · Mar 9, 2015

My first thought was a vacuum leak somewhere, we replaced all the hoses, plugged the AAV line, checked the TPS and ran a propane torch (unlit) around all the connections.

Still at a loss, but thanks all for the replies

Is it possible the wrong fuel ECU could cause a high idle? We are running a used one from a parts car of a different year.

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Gubi

· #11 · Mar 9, 2015

You check the timing advance?

What ever happened with the drive relay? Did the new one fix the problem?

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Gubi

· #12 · Mar 9, 2015

Also, do you have the correct idle o ring? It's thicker than most of that outer radius.

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930cabman

Discussion Starter · #13 · Mar 9, 2015

New drive relay is working great, thanks. "O" ring appears correct, it ha s a greater cross section than we normally see and is working. Next tme in the shop I will check the accordion hose for cracking/splits.

I had thought the wiring was going to be a real problem, but with the help from a color coded wiring diagram from Papajam it has been straightforward. We did change the fusebox, all the relays and several connections although. Thanks for a parts car

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High Idle

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