3.6 conversion, high idle. Good otherwise. Help!

[LeftCoastErik]

Just completed the 3.6 conversion in my SC. Runs great, no stalling or anything, just a high idle. Steady 11-1200rpm. No dips under decel or anything. It has a custom chip in the DME (that was all running in the 964 donor) That car had a lightweight clutch/flywheel and so do I.

I have smoke and brake clean-tested the intake and vacuum systems with no appreciable leaks.
Verified the throttle plate is closed and he microswitch is adjusted correctly and I believe it is working.

Pulled the ISV and it looked pretty darned clean, but I cleaned it anyway and also bench tested it. It seems to work as it should. Things I have tried with it:
1. Pinch off the air from the ISV into the engine. Engine idles at about 900 like it should
2. Unplug ISV, same result as above (I believe this means that the ISV is able to close far enough to allow proper idle speed, but is being told to stay open.) But, of course, in this state it is pretty cranky under decal, so not a good solution.

Any thoughts? Nobody around here has a Hammer to play with. I also don't have the stock chip to try out to see if the issue is in the programming. I can live with it, but it is a little annoying.

Thanks!

[ischmitz]

With the air tube from the ICV pinched the engine should be about dying. I assume your throttle plate isn't closing against it stop properly. Check your throttle cable or linkage is allowing the throttle plate to close all the way. There is a hard stop.

[LeftCoastErik]

Thanks for the response!
I have disconnected the cable and loosened the screws on the microswitch to allow it to come all the way down. No difference there. I have not messed with anything on the AFM or Throttle, is there any adjustment there?

[ischmitz]

There are independent adjustments for the mechanic throttle stop and the micro switch position. The throttle stop is adjusted so that the ICV is in its "happy" place of about 60% duty cycle while the engine is idling (with the micro switch depressed). This needs to be done with the engine fully warmed up.

Then the micro switch it adjusted so it doesn't act as a mechanic throttle stop taking the full force of the returning lever. It just has to be getting actuated rather than acting as the mechanic stop.

Unfortunately, without a Hammer or PST-2 it's hard to tell the duty cycle of the ICV when you move the throttle stop. You could try removing the micro switch and activating it with a zip tie. Then by carefully adjusting the throttle stop while the engine idles you should find a range where the ICV is active and able to maintain the 880RPM. Set the stop to the middle of that range and see if that works. Then mount and adjust the micro switch and confirm it'll trigger when the throttle is closed.

Of course this all assumes no other vacuum leaks.
Ingo

[pors1968]

Did you check head temp sensor .

[LeftCoastErik]

pors1968 I did not. What should I look for? Can I back probe or check resistance on the sensor to verify its ok?

[LeftCoastErik]

Ok found the specs. Will check. Though it isn't running rich or having an issue starting.

[LeftCoastErik]

I rechecked for vacuum leaks last night, going as far as unplugging and capping the vacuum to the vent and charcoal canisters to make sure there were no oddball leaks there. No change. I am leaning towards the ISV. Most descriptions I see indicate a 3-wire hookup, but my ISV has only a 2 wire plug. The engine is a 1990 model, so maybe the early ones were 2-wire?
In any event it does not vibrate or make any noise with key on-engine off. I can hit it with 9v and it will open up and come back to rest with around a 1/8" gap.

Also to clarify my earlier statement. If I COMPLETELY pinch off the air to the engine, it stalls out. This would seem to eliminate vacuum leaks as the problem and point to either the ISV or the Chip being programmed with a high idle (to compensate for the flywheel?) If I pinch it halfway, it will drop the idle down. Unplugging the ISV also drops the idle to 900ish. So either it is being commanded to a higher duty cycle and thus idling high or the ISV is not closing all the way.

Im thinking anyway..lol

[ischmitz]

The ICV on a 964 engine is a two-pin device and it does not vibrate like the 3.2 version. If you don't have access to a hammer another way to test is my looking at it moving while the engine is running.

Remove the ICV from the rubber tubes but leave it connected. Use vise grips to almost pinch off the rubber tube going into the inlet and try to get the engine started and idling (adjust the amount of pinching to get about 1100 RPM). Then when you ever so slightly block the pinched off section of tubing the engine speed should decrease below 880 and the ICV should open trying to compensate for that. You need to see the valve moving. If it sits still either the ICV or the harness or the DME itself is damaged.

You 9V battery test tells us the ICV is not completely dead and able to move. So chances are it's OK. If it was very gummed up internally it would react sluggish and not catch decal events properly. This leaves the +12V supply on one of the pins or the DME.

Also, it is extremely unlikely that the chip was changed for a 1200RPM idle. There are other changes for the light flywheel but raising the idle would be very strange indeed. For a race car MAYBE, but for a street car NO WAY. Do you have a stock chip to try.

Ingo

[LeftCoastErik]

Thanks Ingo. I just disconnected throttle cable and played with the throttle stop. I got it to drop about 50rpm. Micro switch is working. So is the ISV, per your test. It runs perfect otherwise. So I have to assume it's the chip. I don't have another chip to test but I will see if I can scare one up

[LeftCoastErik]

Finally got ahold of the original owner of the engine. Turns out it was set to idle around 1100 when the chip was custom burned.

[ischmitz]

Ok, good find. I'd go back to a stock chip, preferably the with the '89 setting for the lighter flywheel and see if that works better for your application.

Cheers,
Ingo

[uwanna]

Originally Posted by ischmitz

Ok, good find. I'd go back to a stock chip, preferably the with the '89 setting for the lighter flywheel and see if that works better for your application.

Cheers,
Ingo

Ingo,
I have a couple of 964 DME ECUs. One is from an '89 with lighter flywheel, the other is from a later car. Over the years I've done some chip swapping and now have the original chips on hand, not installed. My dilema is, I didn't mark the chips as to which ECU they came from. The part# stickers on the chips are as follows 1267356142 and
2 267 356 905.
Given your experience with 964 chips, any chance you could identify which chip is the
'89 light flywheel model?
Appreciate any help,
Grant

[ischmitz]

The 1.267.356.142 is from the '89 DME
I don't recognize the other number as a 964 DME chip. It should read something like 1.267.35x.xxx

Ingo

[uwanna]

Originally Posted by ischmitz

The 1.267.356.142 is from the '89 DME
I don't recognize the other number as a 964 DME chip. It should read something like 1.267.35x.xxx

Ingo

Ingo,
Thanks, now I know which box to put the chip in.
I missread the other chip, the correct # is 2.287.356.905 and it definatly came out of a later 964 ECU as it has the stock type printed sticker and I removed it from a previously
unopened ECU. Also ran it for a while.

[uwanna]

Originally Posted by uwanna

Ingo,
Thanks, now I know which box to put the chip in.
I missread the other chip, the correct # is 2.287.356.905 and it definatly came out of a later 964 ECU as it has the stock type printed sticker and I removed it from a previously
unopened ECU. Also ran it for a while.

Ingo,
You are correct that 2.287.356.905 doesn't appear to be a 964 chip so I'm really perplexed. Here's a chart of all the ECU #s and the Eprom #s.