Need help with idle issue

[reefdiver]

Need some help.
I have about 50 miles on my 3.4 rebuild. Getting no help from Patrick Motorsports who completed engine build and my frustrations are growing.

My issue: I cannot properly adjust my base idle (880 to 900) nor can I make changes by adjusting the Co2 level screw on the AFR. I cannot get the car to idle lower than 1000 rpm and could not affect the Co2 by the AFR adjustment screw.

I have discussed the matter with both Steve W (who sold my engine builder the current chip) and Sal who has been the most helpful. I have followed both their recommendations but cannot resolve my issue nor can I find one like it on the forum.
What have I done or checked:

- All vacuum hoses were new during build. All have been checked, re-check, and checked again. Only issue with vacuum is when I take off the oil cap, the RPM does not reduce as it should (believe this is a clue, but not sure to what?).

- Replaced fuel pressure regulator last week. And pressure is at 35 PSI.

- Pulled vacuum line off fuel dampener and identified no change in RPM or smell of fuel.

- Sent AFM out and had Bavarian Restoration refurb the part.

- Checked continuity on idle micro switch operates properly

- Pulled computer and ensured Motronic fuel quality switch was at zero. No change.

- Check continuity of the two switches and continuity.

- Cleaned the ICV and checked continuity.

- Installed AEM UEGO gauge to monitor air fuel ratio.

- Check part numbers of all injectors (which were cleaned and refurb during engine build).

- Unplugged each and found no drop in RPM as each was disconnected. Reinstalled today.

Still can’t get idle lower then 1000 rpm, AEM bounces between 14.2 and 15.5 when warm, and adjustments to Co2 level on AFM makes no change to AFR range.

I may need to take it to a pro.

[Eric D.]

Sounds like a vacuum leak. Something easy to try, Try pinching off those vacuum lines one at a time, See if it changes anything. Or spray carb clean or silicone spray something flammable around the intake and gaskets. If you idle momentarily comes down you may have found a leak.

[reefdiver]

No change. Still can't get a change when adjusting the AFM Co2 screw either. I don't thnk its a vacuum issue.

[76FJ55]

I am assuming you are following the manual procedure by bridging contacts B and C on the test socket in the engine bay? Also are you doing the adjustments open loop with the O2 disconnected? In closed loop the O2 system will be fighting you when trying to adjust mixture. hook up a vacuum gauge to measure intake manifold vacuum at idle.

[techman1]

Paul,

Do you get the same idle speed cold and warm?
Have you confirmed the idle switch is engaging when closed, ensuring it is going into the idle circuit?
Shold be able to hear it click, and make sure it is plugged in, wires intact. Sounds like it is never entering the idle function.

[stlrj]

Paul,

You never mentioned making any basic adjustments to the idle air bypass on the throttle body. Seems you've done everything else, aside from rebuilding the engine.

Joe

[T77911S]

it really sounds vacuum related.
check intake bolts


what about the throttle switch and circuitry.

[stlrj]

" could not affect the Co2 by the AFR adjustment screw."

Do you mean the CO adjustment screw on the AFM? 'cuz CO2 is the fizz they put in soda.

[reefdiver]

J6FJ55

Yes, I am bridging contacts B and C on the test socket in the engine bay when attempting to adjust the idle air bypass screw.

stirj,

To funny. Yes. Co.

Engine was a complete rebuild by Patrick Motorsports that was shipped back to me in April. Idle air bypass screw is all the way in and the low that I can obtain is 1000 rpm. That's at cold start. When warm it drops to 900-940.

- I can also hear the idle click when the throttle is moved slightly.

Question: If it clicks, could it still be bad? And if its bad what are the symptoms?

Also, read on another post that the gasket in the ICV could go bad. I might try a vacuum test on that and see if it holds pressure.

[reefdiver]

For those trying to help, my engine build/ restoration is on this page. Might help if you have an idea of what was done.


1987 Porsche 911 Restoration

[reefdiver]

Also checked intake bolts, which received new gaskets during build. all at 18 foot pounds.

[T77911S]

any chance there is a problem with the brake booster hose. did you connect the booster hose.

[reefdiver]

Checked the brake booster hose by disconnecting it and plugging the hose on the engine side. No change in RPM.

[techman1]

Paul,

I believe you can check the idle circuit with this method.
If the idle switch is depressed and the idle goes over about 1200, the dme will cut out and the idle will drop, then pick back up etc. as if you are blipping the throttle.
I found out with a little contortionism you can lift the throttle in engine compartment a little and I used a screwdriver to depress the idle switch. If the idle is above 1200, it should drop.

[reefdiver]

techman1,

First off, thanks for the help. Just did the test and when I applied the tip of the screw driver to the little button/idle switch it went down and then immediately went up and started to idle hunt, which was weird. Right? Felt like it wanted to drop but then hunted, which was not my issue. Is this telling us the idle switch bad?

[Funracer]

Recently bought an 83SC. Just spent 2 months trying to get the idle to drop from 1100 to 950.
Checked every vacume hose several times. Turned out the idle timing was too advanced causing a high idle. Have you verified the idle timing correct?
Good luck

[reefdiver]

Funracer,

Thanks for the input. On the 87 the motronic system controls the timing and I have been told by Steve Wong that, "There are never any problems with my chips" but I'll keep that in mind as we move forward.

[techman1]

If the idle is over 1200 and you engage the idle switch (also called the throttle closed switch)
The dme will try to adjust the speed by closing the icv. When that does not drop the speed enough, I believe it cuts the injector pulse. Not sure about that. However it will seem like the idle is hunting, so sounds like that switch is working, just make sure when the throttle is closed it is engaging the switch.

[dan88911]

Smoke test for possible vacuum leaks.

[techman1]

Hmm. Just thinking. IF the idle switch is closed, the ecu should be telling the icv to close all the way.
If the idle is still st 7-800 plus, something is giving it air, or the isv is not closing.

Remove it. Plug both hoses. Start the car. If it runs, in air is getting in somewhere. If it does not even try, the isv is what was open, letting in too much air.