Cold start/idle issue: '87 Carrera

[Lyle O]

Hello, team. I’m going nuts on this… One of the things that has always impressed me about my car ( ’87 Carrera) has been the cold-starting capability. Literally, when I would turn the ignition key, it would start in about ¼ of a revolution, and have a nice smooth idle (about 1100 rpm at first, then settle to 880 within a few minutes). Absolutely perfect for the past 5 years at least, including an engine rebuild a year ago, etc. About a week ago, however, I went to start one morning, and, while it fired right up, it wouldn’t maintain a high enough idle to stay running. I got it to run by nursing the throttle for a few minutes, and it then would idle, though lower than normal at first, then moving to 880. I took the car for a spirited drive, and it ran great after that initial few minutes of warm-up. All great. Hot starting later was perfect also. The next morning, same issue, and that’s what I have now. Through what I have gleaned from searches here, I have checked the following:

• I swapped out my DME relay with my known-functioning back-up (no improvement).
• ICV is buzzing when I turn the ignition on.
• ICV input resistance on center and each of the outer terminals is within spec (22 and 44 ohms, respectively).
• When I put a volt meter to the center terminal of the ICV connector (with ignition on), I read 12 volts when grounded to an outside terminal.
• All the other sensors (speed, CHT, and reference) are in place and connected as far as I can tell.
• CHT measures ~2000 ohms when the engine is cold.
• I figured this could be an ICV issue, so I pulled it and cleaned the valve with carb cleaner; it moves freely. I reinstalled it, and watched the valve move closed when I energized it. But the issue remains.
• I tried unplugging the O2 sensor as well when cold, but it also made no difference.
• As a side note, I had the injectors cleaned and flow tested last year.

What am I missing? I am not very electrically sophisticated, but I can do some basic tests (I have a multi-meter). Would CHT have an effect here, even though it seems to check out OK (I thought that, in the absence of a CHT signal the DME thinks the engine is cold, and runs those maps. In my case, it doesn’t seem to know the engine is cold)? Could it be AFM related? Have I developed a big vacuum leak someplace (nothing apparent that I can see).

Again, the thing is, the issue happend from one day to the next, and is only present the first 2 minutes or so when cold. Once it runs a bit, it idles, and warms up and runs perfectly.

Thanks a lot for your help.

Lyle.

[ischmitz]

First thing: It the idle switch engaging when the throttle is in its resting position. It's a small micro-switch that sits on the throttle body and tells the DME to go into idle mode.

Ingo

[Lyle O]

Originally Posted by ischmitz

First thing: It the idle switch engaging when the throttle is in its resting position. It's a small micro-switch that sits on the throttle body and tells the DME to go into idle mode.

Ingo

Thank you, Ingo for jumping in...

Yes, the switch is engaging properly. I guess I do not know if it is functioning, though. Is there an easy way to test it?

[cabmandone]

If you have an ohm meter you can unplug it and check to make sure it's opening and closing. Just connect the meter to the pins then take your hand and roll the throttle by hand

[Lyle O]

OK thanks.

I checked the throttle switch; it shows "0" ohms when closed (actually 2 or 3 on my meter at the lowest setting), and infinite when rolled open (I can hear the switch "click"), so it seems to be functioning properly.

What else should I check?

Thanks again.

Lyle.

[DRACO A5OG]

"past 5 Years", in this time was the battery ever changed?

In the morning what is the voltage when cold? Please post.

The reason she seems normal after warm up the battery is replenished enough.

"Rebuild a year ago" check the gear box to chassis ground and the engine bay ground too. As the engine heats up, the heat expands metals and allow a more solid contact.

[Lyle O]

Originally Posted by DRACO A5OG

"past 5 Years", in this time was the battery ever changed?

In the morning what is the voltage when cold? Please post.

The reason she seems normal after warm up the battery is replenished enough.

"Rebuild a year ago" check the gear box to chassis ground and the engine bay ground too. As the engine heats up, the heat expands metals and allow a more solid contact.

Thanks, DRACO;

Battery is 6 years old (from 2010). Morning voltage today reads 12 volts (per the volt meter I have stuck in the cigerette lighter). It has been great, though I left the glovebox door open a year or two ago and had to jump it then. I keep a tender on it during the winter months.

I just double checked the chassis ground at the trans. It looks like it was not uncoupled when the motor and trans were dropped 18 months ago. The ground strap looks good, though, and where it attaches to the body/chassis was ground fresh, and there is a new stud and nut there (See photo here).


I will clean up where the strap attaches to the trans, though.



Any other things to check? Thanks again.

Lyle.

[cabmandone]

If I'm reading this right, your issue appears to have begun after an engine drop, rebuild and reinstall. I am correct in that? Or did it run fine after the install and just now develop this issue?

Also, when you cold start it sounds like it stumbles then idle searches right? Did anyone mess with the base idle mixture screw on the AFM?

[Lyle O]

Thanks a lot, Cabmando. Sorry if was not clear...The issue began just a week ago, and it was sudden: one day to the next. I have put almost 2,000 miles on the motor since it was dropped, rebuilt, and re-installed last summer. All 2,000 miles were great (had the prescribed 3 oil changes, a valve adjustment, etc.). Since the motor went back in, it started, idled, and ran perfectly (until last week). To my knowlege, nothing was done on the AFM (also nothing apparent at the loction where I think you would have to drill out the epoxy, adjust, and re-seal it), but I will check with the engine rebuilder tomorrow.

It is not so much that it stumbles; it just will not idle for the first 1-2 minutes unless I give it throttle. After that, it seems to be warm enough that it will stay running without throttle input (500-600 rpm at first, then moving up to 880).

Lyle.

[cabmandone]

You were probably clear it's just my mind isn't

When you have it warmed up and running right have you taken the oil fill cap off to see if the idle drops? It sounds to me like you might have some unmetered air coming in throwing off the idle when cold. I could be wrong there.

BTW, as I understand it I think there is just a cap on the bottom of the AFM that is removed. Mine wasn't there so I knew someone had messed with my setup. When I installed my Wideband I found my idle mixture was way off which caused a rich condition which IIRC also caused my idle searching.

[Lyle O]

Originally Posted by cabmando

When you have it warmed up and running right have you taken the oil fill cap off to see if the idle drops? It sounds to me like you might have some unmetered air coming in throwing off the idle when cold. I could be wrong there.

Yes, I tried that. It changes a little (but only a little). I think you make a good point about a vacuum leak or extra air, but I can't see anything overt. Next step there I think will be to spray some carb cleaner around the vacuum lines and see if something happens (besides an engine fire ). Still, because of the suddenness of the issue, it's like a hose or connection would have to have come loose or apart.

Thanks for the help...

[cabmandone]

Originally Posted by Lyle O

Yes, I tried that. It changes a little (but only a little). I think you make a good point about a vacuum leak or extra air, but I can't see anything overt. Next step there I think will be to spray some carb cleaner around the vacuum lines and see if something happens (besides an engine fire ). Still, because of the suddenness of the issue, it's like a hose or connection would have to have come loose or apart.

Thanks for the help...

If you look I think there is a safer method using smoke to test for vacuum leaks. Just a thought but could an intake gasket have developed a leak? It wouldn't appear visibly without taking the intake runners off. I think there is also a propane test you can do with a torch and a hose directing propane to the potentially leaking areas.

[Lyle O]

Thanks again. I went through last night and checked all of my intake runner attachment torques, and did find a few that were looser than I expected, so I re-tighted them. Unfortunately, still no change. I will do some more searches on finding leaks by using carb cleaner or propane before I try that (I am nervous about doing it that way); if anyone knows a safer, simple way, I would sure be interested. I will also take a better look at my AFM to look for the cap you mention (may need to remove it from the car to do that?).

Per DRACO's suggestion, I have put my battery back on the tender, and will next check it when it is fully charged, just to see if helps. I will also remove and clean up the ground point at the trans. I figure that 12 volts should be good starting operating voltage. However, I am not at all too proud to be proven wrong on that!

Anyone else have any ideas on what to check next? Is it possible there is a problem within the DME itself?

Thanks a lot, all.

Lyle.

[Quicksilver]

When the intake gets loose it can allow the intake gaskets to crack giving you a leak that won't go away. The effect at idle of a leak can be a bit different depending on which cylinder has the leak. Takes some 'splaining...
The DME fires all the injectors at once so all the intake runners are getting sprayed at a different time during the induction cycle. If you have a vacuum leak on a cylinder where the injector fires right before the intake opens you will get a very limited effect from the issue. If the vacuum leak is in a port where it has some time before the intake opens the charge can be drawn out of that runner towards one of the other ports. In that case the port will be very lean or just plain dry.

You can test to see if you have a "specific port based issue" like an intake gasket leak with a IR thermometer gun. Get the car up on stands while it is cold and then start it. Crawl under and measure the different exhaust port temps as it heats up. If there are specific cylinders that get warm slowly you know you need to check those cylinders. Vacuum leaks, injectors, spark...
When I chased down the vacuum leaks during my "Rubber Explosion™" incident I was seeing some ports that were under 110° when other ports were at 250°! I had 4 ports with cracked gaskets, eroded port insulators, multiple cracked hoses, fuel line crimps that spun like a bearing, and a DME with multiple failed solder joints.

Test, test, test!!!

[rick-l]

Just a note.

My 88 used to hunt idle speed at startup and sometimes stall. I kept reading it was because of basic mixture settings but I had no way to measure CO so I lived with it.

It went away after I changed injectors.

[scarceller]

We really need to know what your mixture is doing. Do you have access to a WideBand O2 gauge? Without knowing the mixture we really have no idea if you have a lean issue. I suspect you may have developed an air leak but we need proof.

[Lyle O]

Originally Posted by scarceller

We really need to know what your mixture is doing. Do you have access to a WideBand O2 gauge? Without knowing the mixture we really have no idea if you have a lean issue. I suspect you may have developed an air leak but we need proof.

Thanks, Sal, you are absolutely right; I don't know my AFRs. I need to get that. I will try to get a wide band unit, even if I have to buy one (I've been wanting to get one anyhow). I will work on that next...

[scarceller]

See this thread on WBO2 units, get a unit with the LSU 4.9 sensor
AEM Wideband O2 gauges
I suspect a mixture problem and we need to know how far off it may be.

Originally Posted by Lyle O

Thanks, Sal, you are absolutely right; I don't know my AFRs. I need to get that. I will try to get a wide band unit, even if I have to buy one (I've been wanting to get one anyhow). I will work on that next...

[ischmitz]

I had an issue recently with my 3.6 (it's a close relative to the 3.2 in terms of fueling and sparking) that might be somewhat similar. Same as in your case the car normally would start up on the first turn of the key like clock-work.

Then one day it took quite a bit of cranking until it finally came up. Idle was OK but it seemed it was struggling the first 10 - 20 seconds. I didn't think much about it and filed it under "hm....". A couple of days later during cranking I couldn't get it to start after five tries. I quickly went through my mental troubleshooting, sprayed brake cleaner into the intake, cranked and it fired right up and set into a perfect idle. Ran fine with no issues that day and for the next couple of days it started just fine.

After that I drove the car several weeks, all the way up to the Bay Area and back. I put the can of brake cleaner in the trunk just in case. No issues, it ran for a week like nothing ever happened. Then it sat again for a couple of weeks and I had all but forgotten about the issue thinking it was maybe a bad tank of gas or something. But you guessed it, problems rarely fix themselves

The next time I wanted to start - nothing, It cranked like crazy and not even a stumble. I was afraid I'd drain the battery or fry the starter. Brake cleaner made it run on just that but there was no fuel. At some point I got it to stumble-run on what sounded like 2 or 3 cylinders only. As soon as I touched the throttle it would die. Then 10 minutes later after more brake cleaner treatments it ran somewhat, I reved it, got out of the garage thinking it's getting better and it died again. This time I had to get a ride to work.

My focus went to the fuel delivery system (pump and filter). That night I swapped the filter first. And guess what. Looks like problem solved. I cut the old filter (964 style) open with a dremel and it looked perfectly clean inside. The paper had the same color inside and outside. There is no valve in this filter, it's just paper supported on a plastic carrier.

That's where I am right now. Still planing to replace the fuel pump since mine is the old '74 model that might be original to the car. I want to go to the larger 964 style. And I still don't understand how a filter would go from making starting a little hard to then letting the car run at peak performance for 700 miles to then preventing the car from even starting. Makes no sense to me.....

One Porsche mechanic friend of mine explained to me that a dying fuel pump is known to struggle at first when cold to male fuel pressure. And that the brake cleaner that makes the engine run also vibrates the chassis enough to where this makes the pump run and once the pump can make pressure it;s support the engine. He also said a dying fuel pump is known to clog up the fuel filter. Well, I haven't seen anything large in my old filter. So my jury is still out on that.

I don't think the DME is suspect in your case. It is more likely related to mixture. Good luck with your testing and keep us posted.

Ingo

[scarceller]

Ingo,

If you are correct then maybe just hot wiring the FP fuse to let the pump run for 15 seconds before you crank should prove your theory. Or simply hot wire the FP fuse and leave it jumpered and wait 15 seconds then proceed to start the car. This will allow ample time for pressure to come up prior to cranking?

Or possibly cranking on a low battery causes the pump to under deliver?

Maybe a alligator clip jumper would be as good as the starter fluid?

I do think you may be on to something.

Originally Posted by ischmitz

I had an issue recently with my 3.6 (it's a close relative to the 3.2 in terms of fueling and sparking) that might be somewhat similar. Same as in your case the car normally would start up on the first turn of the key like clock-work.

Then one day it took quite a bit of cranking until it finally came up. Idle was OK but it seemed it was struggling the first 10 - 20 seconds. I didn't think much about it and filed it under "hm....". A couple of days later during cranking I couldn't get it to start after five tries. I quickly went through my mental troubleshooting, sprayed brake cleaner into the intake, cranked and it fired right up and set into a perfect idle. Ran fine with no issues that day and for the next couple of days it started just fine.

After that I drove the car several weeks, all the way up to the Bay Area and back. I put the can of brake cleaner in the trunk just in case. No issues, it ran for a week like nothing ever happened. Then it sat again for a couple of weeks and I had all but forgotten about the issue thinking it was maybe a bad tank of gas or something. But you guessed it, problems rarely fix themselves

The next time I wanted to start - nothing, It cranked like crazy and not even a stumble. I was afraid I'd drain the battery or fry the starter. Brake cleaner made it run on just that but there was no fuel. At some point I got it to stumble-run on what sounded like 2 or 3 cylinders only. As soon as I touched the throttle it would die. Then 10 minutes later after more brake cleaner treatments it ran somewhat, I reved it, got out of the garage thinking it's getting better and it died again. This time I had to get a ride to work.

My focus went to the fuel delivery system (pump and filter). That night I swapped the filter first. And guess what. Looks like problem solved. I cut the old filter (964 style) open with a dremel and it looked perfectly clean inside. The paper had the same color inside and outside. There is no valve in this filter, it's just paper supported on a plastic carrier.

That's where I am right now. Still planing to replace the fuel pump since mine is the old '74 model that might be original to the car. I want to go to the larger 964 style. And I still don't understand how a filter would go from making starting a little hard to then letting the car run at peak performance for 700 miles to then preventing the car from even starting. Makes no sense to me.....

One Porsche mechanic friend of mine explained to me that a dying fuel pump is known to struggle at first when cold to male fuel pressure. And that the brake cleaner that makes the engine run also vibrates the chassis enough to where this makes the pump run and once the pump can make pressure it;s support the engine. He also said a dying fuel pump is known to clog up the fuel filter. Well, I haven't seen anything large in my old filter. So my jury is still out on that.

I don't think the DME is suspect in your case. It is more likely related to mixture. Good luck with your testing and keep us posted.

Ingo