Replaced ICV

[Mark's 86]

I have an 1986 3.2L Carrera that has always struggled with an unstable cold idle. The car has had the intake spacers and gaskets replaced, new fuel lines, new speed reference sensors installed, new CHT sensor, new plugs, cap rotor, wires, The base idle speed and CO set as per factory specs. The unstable cold idle still exists. The car starts fine and Idles good when cold but if you rev it up under no load and take your foot off the gas it tends to stall. after a few minutes this becomes a non issue and the idle recovers properly with no tendency to stall. Today I replaced the original ICV and hoses. Problem solved!!!!! Car starts great cold and goes into a proper cold high idle (aprox 1100 rpm) I can now rev it up cold under no load and the idle stabilizes with no tendency to stall. The original hoses were in surprisingly good shape. The ICV had never been serviced (87,000 original miles) and was quite gummed up. I cleaned the original ICV with throttle body cleaner and will keep it as a spare along with the original hoses. I read a Road and Track review of the 3.2 Carrera from 1984 and it commented on how the ICV struggled to stabilized the idle especially when cold. I have always assumed that this was just the nature of the beast?

[steely]

Congrats! My cars previous owner chased this problem down and never solved it. It wasn't so much of an issue when the car lived in Alabama, but still, he bought a new ICV with limited results. When I bought the car up to Penna, the problem got worse in the Fall cold. In my case, the DME drivers were burnt out, so the old and new ICVs were never actually driven. I fixed that and it works great, and in the past 7 years I haven't had any issues like those mentioned in that R&T article.

nice work, and yes, keep the spare.

[Mark's 86]

Hi Dan,

Out of curiosity can you elaborate on the ICV drivers and where they are located and how you test them?

Mark

[steely]

Hi Mark,

I think the bentley manual mentions this, and there is a DME engine management book out there to if you are interested, but I will certainly try. I will also mention that my problem seemed to be an oddball.

The ICV is like a servo motor, and it has 2 windings. The DME controls or drives each winding, one side more that the other sometimes, in order to position it open, closed, or in between. Instead of sending a power signal to each winding, it sends one power line that the windings share, and the DME controls the ground path to each winding in order to operate it.

This driving happens many times a second, and causes the vibration you feel on the ICV (when the DME is on). Mine wasn't buzzing at all.

If it isn't buzzing, it is either the ICV or the DME.
If you do a resistance check of the ICV and each winding leg reads something like 20 ohm (~40 +/- across both), then the ICV is good.

This "using the ground paths" to control the ICV can throw some folks off, since, they may see +12V coming from the DME, and think all is well.

The 2 switches in the DME that do this job are transistors. For some reason I do not know, one of mine was dead.

The way to test them: Use a Scope to see if the signals are present by breaking-out each ground side of the ICV or by simulating the ICV with a load.

There are schematics out there for the DME if you are interested, and the dorkiphus site has some explanations about some of the functions.

Here is the fun I had:
3.2 cold start issues

This was my only claim to fame - there are others who know s-loads more about everything else on these cool cars.

[sugarwood]

My idle is fine, but is it relatively straightforward to remove the ICV and clean it?
Or should I let sleeping dogs lie?

[steely]

Originally Posted by sugarwood

My idle is fine, but is it relatively straightforward to remove the ICV and clean it?
Or should I let sleeping dogs lie?

It's pretty easy.
ICV removal & cleaning

[darrin]

Originally Posted by sugarwood

My idle is fine, but is it relatively straightforward to remove the ICV and clean it?
Or should I let sleeping dogs lie?

IMO, if it ain't broke, don't fix it --