negatives of disconnecting VCM

[madkaw]

I been trying to figure out my bad idling issue on my 81zxt. When hot especially-the engine idled like crap and surged slightly at most rpms not under load. I say not under load because during cruise the car seemed to run well. After checking many basics on the car I decided to start pulling stuff and see how it effects the running of the engine. I pulled the EGR vacuum line and it immediately ran better. I diconnected the anything to do with the VCM, electrical and vacuum and the car runs better then it ever did. The idle smoothed out and the slight hesitation off line got better.

Before doing this disconnect process, I pulled my relatively new spark plugs and they looked like they were fouling under idle , but the cleaned up themselves after driving. I say that because the end threads has some carbon deposits, but the electrode almost looked lean. Except for color left by the injector cleaner I am running, the plug was petty clean.

 

Also noted: is that doing all the OHM tests according to the FSM, the car passed except for the CHTS. At the ECM the CHTS failed the ohm test, but the sensor component check seemed to look good. My connector looks servicable and I cleaned it also. Maybe my problems are all tied together here, I don't know enough about EFI to say.

[DuoWing]

You can completely remove the VCM and it's components and have your car run fine. I had done this on my 280ZXT. I removed the AAC valve and blocked it off, I left the EGR on just didn't run a vacuum hose to it, and there's one other little valve that the 4-way split runs to and that's the VCV valve. I plugged that off with a drain plug for the L-series oil pan. Now one thing that may happen is that your car will not idle or barely idle. You will just need to adjust the little nut on the throttle body for the throttle stop to allow the throttle body to sit open a little more at idle until you get to proper idle and you'll be good to go.

[RUZN]

yeah I did the same. NO VCM, AAC, EGR anything lol all looped into eachother doing absolutely nothing haha.. Then just adjusted the TB to be a crack open and got a decent 900rpm idle. It might sputter occasionally but shes a great runner.. Easily 130mph lol

Edited May 23, 2009 by RUZN
poor spelling lol

[HowlerMonkey]

I found that the warmup regulator and the idle air control were both stuck open on mine and that someone had adjusted down the throttle plate to compensate.

 

I replaced that metal spider of hoses between the parts one hose that goes between idle air control and warmup regulator and another one that goes from the one way valve on the manifold to the barb on the turbo pressure tube.

 

After that, I replaced that crappy screw stop and locknut on the throttle body (idle) with a longer bolt and a nut of a larger outside diameter than the bolt head.

 

I also cleaned the throttle body which I found amazingly gummed up.

 

Everything is fine now and I've moved on to the M30 ecu so I now have a standalone 1981 setup complete in a box I keep in the trunk and a fuel pump jumper wire for an emergency engine management system.

 

I still have egr control and a/c idle up working.

[DuoWing]

I forgot about the idle up for A/C. My A/C didn't really work so I removed the belt from the compressor so I never had to worry about it. Like I said though I did keep the air regulator for the fast idle on cold starts, that helps alot especially since I drove my Z daily through the winter. That fast idle made a world of difference on those 10*F and colder days.