Lowered the idle, now I get engine clunking?
 

I have an '85 3.2 with ~95,000 on the clock. I recently installed a Steve Wong chip and modified the ECU to the 4k specs. Being someone who generally takes things in slow steps, I left the idle adjustment alone until I was sure everything else was happy.

Last Saturday I decided to finally lower the idle after getting home from a long drive. I dialed it down to ~900rpm from 1100-1200rpm, and she seemed to settle out. I had my fiance pull the 911 into the garage so I could listen to the changes on the way in, but her foot slipped and the car stalled.

Here is where it gets weird. She goes to restart it and nothing(never had an issue ever). Car cranks once like it has a dead battery but gets no further. She gets out and we start to push it in. I decide to give it another shot after a bit of pushing, and low and behold she fires right up. Downside is, now she is making quite a bit of clunking. I pull into the garage and turn her off.

Sunday I head out to the garage again and fire her up. Idle bounces up, down, up, down, up, down, and then settles. Engine is making a fair bit of clunking at idle. Slight tap of the gas(2k-3k rpms) seems to make it go away?

Any thoughts?

Looks like I might not have had the jumper engaged completely, will play around with this tonight and report back.

the idle is not adjustable.

So what is this?


911Chips.com - Motronic DME Update

You should also check your idle position switch.

Would that be impacted by my adjustment of the screw without properly jumping the pins? I only ask because I'm hesitant to spread the problem if I just need to adjust it back slightly.

What you are setting is the base idle speed with with the idle control disabled. This is so the DME is adjusting the idle up and down with small amounts of input from the idle air control valve around what it should be.

The 2k 4k just refers to the amount of memory for the program in the chip.

If your idle was 1200 rpm either the engine was cold or the idle switch was open.

Edit: or your idle air control is stuck

Right. Is that not something I need to do post ECU modification?

Does this mean the engine rotated until it hit a compression stroke and the lights went out?
Battery terminals?

It does not have anything to do with whether the idle is adjustable or not which is what the response was.

No, it means it acted as if they was almost no power to crank the starter. Lights and everything else are fine, battery is clearly charged. I would ignore this aspect for now as it hasn't happened since.

Ah, forgive my ignorance on this then. Basically, all I'm trying to do is set the idle back to where it should be post ECU modding as per those instructions. I now believe I didn't have the jumper properly engaged, which means the electronic idle controls would be fighting my manual adjustments correct?

This is incorrect - the link that you (TheSt|g) posted from Steve Wong does indeed show how to adjust your idle (and I've done this on my 3.2).

I can't say for sure whether or not your idle needs to be adjusted, but the idle on the 3.2 Carrera is indeed adjustable. When I first tried to adjust my idle, it was initially too low, and once the car heated up, the idle on my car would bounce in the same way that you described in your car (except that there was no clunking noise from my car). In my experience, the idle adjustment was somewhat finicky to get right, you may want to keep working at it.

its not suppose to be messed with. if the idle changes on the car, something else is wrong.

So you are saying that Steve W is wrong on his chips and the idle shouldn't be touched after modifying the ECU?

What he means here is that, when the throttle is at idle position, there is a switch on the back of the black rubber intake elbow that is supposed to get engaged that tells the DME to run at the idle program. If you open the throttle 1 or 2 mm, the idle switch disengages and, per Bentley, automatically causes the rpm to jump up by 500 rpm (and advances the timing).

You can test whether or not the idle switch is working when the engine is shut off by checking continuity. PM me if you need the info from Bentley on how to do this. You can hear the switch click if your garage is quiet enough.

Presumably T77911S hasn't installed a Steve Wong chip. Per Steve's instructions, the idle changed due to the chip installation, and you must adjust the base idle back down to 850 or 880 rpm.

To do this, get the car up to operating temperature (I would expect this is to make sure that the DME is running in the proper mode and not in some warmup mode). Remove the back fuse panel cover and stick a jumper into the necessary holes in the test port. I use a paper clip bent over on itself in order to create the necessary friction so it sticks in the holes.

When you insert the jumper, the DME no longer uses input from the ICV (Idle Control Valve), so you're not trying to hit a moving target. To adjust the idle down you'll have to screw the base idle screw clockwise. There may be a yellow "tamper proof" cap over the adjustment screw that you'll have to remove (i.e. break). A new one is $1.03 from your friendly neighborhood Porsche dealership (ask me how I know).

No disrespect meant to anyone, but the 1 sentence responses are often really cryptic to understand and just serve to make me more confused. Maybe it's just me. I can't typically solve a complex problem in 1 sentence, but no one ever accused me of being the smartest guy in the room.

If you can't get this resolved then I'd contact Steve. He seems to be really helpful on here, especially when it comes to his own products.

Here is a dumb question. DId you bolt the ECU back down? We had a friend make the chip change, and then not bolt the ECU back down under the driver's seat, and the car started doing weird things. It turns out that the box is grounded via the mounting bolts.

Just an idea.

Hugely helpful response. Over communication is always best. ;)

I can double check it, but it seems unlikely that it happened to get loose at the same time as I adjusted the idle screw.

So as an update:

I adjusted the idle properly and it seems to settle into the ~proper range once cold start is over. Not too concerned about hitting the exact figure. What does concern me is that the engine still has that clunky rattle, but only at that lower idle. As soon as I give it a bit of gas it completely goes away and she is smooth.

Do you think the rattle could be in the drivetrain (transmission, spring centered clutch disc) that wasn't noticeable when engine idled at the higher speed? I'd suggest putting in 4th or 5th gear with car stationary, letting out the clutch slowly to the engagement point, and see if rattle goes away.

"clunk" like a rattling metal trash cans?

Take a video clip of it and post it.

Can you tell what area the clunk is from?
I agree with Draco, try to do a video or sound recording of the problem.

Agreed that a recording makes sense, I'll see what I can do tonight. Describing a sound in text is always pretty worthless. :D

As for location, its pretty hard to pin point. I used my stethoscope on each of the intake runners and just got the sound of cold tappy valves, so it doesn't appear to be coming from one of the cylinders specifically.

What would happen if you removed the Wong chip and put the original back in? Or are we past that point, due to the 4k mod?

If the DME was 2K with the 2K chip and it was Modified for the 4K chip you can't just put in the 2K chip. You need to undo the modification. Or better yet obtain a factory 4K chip if possible, if you have a SW 4K chip and a factory 4K chip you can swap them whenever you like.

This is exactly why when I convert DMEs to 8K 1989 chip specs with the 28pin chip I always deliver the DME with the factory 8K chip and then any other of my perf chips of choice.

But I doubt the SW 4K chip is the source of the clunking issue. The SW chips are well done and are a good product. Not sure why you want to go back to a factory chip? Although I agree it's a very nice option to be able to go back to factory chip.

Past that point unless I solder the board again. Frankly, I'd rather not as those ECU case tabs only have so many flexes in them before they break off. I also doubt it is the chip as I've had it in for a few months already with no issue.

To save the tabs on the case I don't crimp them back, I simply use a large tie wrap to hold the case in place. This way if you open the case again you just cut the tie-wrap. Or better yet get a long Velcro strap.

Not a bad idea. Either way though, I suspect it isn't related at this time.

How old is your battery?

6 Months.

If it is running well enough to drive, you can bring it by this evening and we could all brainstorm on it. I have the Bentley and the Pelican Forum at hand.:)

It is an excellent offer, but I'm a bit hesitant to drive it around until I have some idea of where the clunking is coming from. The fact it goes away with any amount of revs seems encouraging though.

Something similar happened with a friends car of a different brand.

He stalled it by slipping off the clutch by accident. Then, it wouldn't turn over after using the starter motor

Eventually we push started it and it had an ungodly clatter.


It turned out to be the clutch. Apparently when he stalled it he sheered the rivets that hold the clutch plates together. It was old and just suddenly failed when his foot slipped off the clutch and it violently engaged.

No other damage, just a blown clutch pack.

If that is the situation with yours it may be that at speed it sits properly but moved around without the centrifugal force from turning higher RPMs?

Interesting thought, I'll get the stethoscope and poke around down there. I didn't notice anything weird about the clutch when I pulled it around into the garage, but frankly I was focusing on the engine.

Any updates? Do we need to get a group to come by and analyze the situation?

You can remove the ac belt and listen then fan belt and listen ( but for a a minute or two no longer ).

CCM, he will come around eventually :D " you can lead a horse..."