Idle adjustment question, Idles high or slowly stalls Options

[emerygt350]

You want it on the advance setting. If you have it on the retard setting you should switch to the rear port on the tb but I found the retard is awful on the 123.

However, I suspect this won't affect the idle, but you never know. I assume you timed it with the vacuum disconnected.

[Superhawk996]

The previous owner had the engine rebuilt a year before I bought the car.

I am very frustrated. My old 1.7 idled rock-solid at 900 RPM, so I know the D-Jet can behave like it is supposed to.
Any more suggestions?

What do you know about the cam?

What’s the status of your vacuum? What is that doing as you try to adjust the bleed? Valves properly adjusted?

[rjames]

Does either of your MPSs hold vacuum?

[emerygt350]

And do put a vacuum gauge or mighty vac on the plenum and see what your vacuum is up to. It can tell you all kinds of important information.

[BillC]

Update: I heard back from Ed Madak at 123Ignition, and he confirmed the distributor should be connected to the retard port at the back of the throttle body, on that timing setting.

Absolutely change that to the rear facing port.

I will change it tonight, after I get home, and will report back.

I assume you timed it with the vacuum disconnected.

Yup, timed with the vacuum hose disconnected and the port on the throttle body plugged.

What do you know about the cam?

Nothing, other than it's supposed to be a stock cam or stock profile.

What’s the status of your vacuum? What is that doing as you try to adjust the bleed? Valves properly adjusted?

Valves are properly adjusted -- I did them before reinstalling the engine in the car, which was probably only 50 miles or so ago.

No idea about the vacuum. I need to hook up a vacuum gauge and see what's going on.

Does either of your MPSs hold vacuum?

Yes, they both hold vacuum.

[brant]

I had the same idle down problem a few years back...
fought and fought with it...

once I rebuilt the throttle body.. eliminated the leaks around the worn butterfly... the problem went away.

how does your butterfly plate look in the TB?

[BillC]

So, more frustration this afternoon, but a small step forward.

I moved the vacuum line from the front port to the rear port. And the off-idle transition does seem to be a little better.

However, the car is still idling high. I played with the idle bleed screw and the knob on the ECU, and got it to the point where it would idle fairly reliably at 1300-1400 RPM. I could sometimes get it down to 1100-1200, but then it would often die after a couple of minutes. It seemed to idle best at 2 clicks counter-clockwise from the melt mark. I believe that makes it leaner, correct?

I did hook up a vacuum gauge. When running at 1400-1600 RPM, the car would idle at 8-10.5 inches of vacuum. Any lower, and the vacuum would drop to to 7-9-ish, and then the vacuum would go toward zero as the car stalled. If I revved it up with the throttle, I could watch the vacuum drop to zero and then rise back up as it settled to idle.

I would have expected the vacuum to be higher at lower RPMs. So, not sure what's going on.

I had the same idle down problem a few years back...
fought and fought with it...

once I rebuilt the throttle body.. eliminated the leaks around the worn butterfly... the problem went away.

how does your butterfly plate look in the TB?

Butterfly plate looks okay. I don't see any light around it, nor is it showing any visible wear on the plate or in the bore. However, the throttle does stick just a little bit when cracking it open. Is that a sign of wear? I had assumed that was the plate sealing against the bore.

[Superhawk996]

I did hook up a vacuum gauge. When running at 1400-1600 RPM, the car would idle at 8-10.5 inches of vacuum. Any lower, and the vacuum would drop to to 7-9-ish, and then the vacuum would go toward zero as the car stalled. If I revved it up with the throttle, I could watch the vacuum drop to zero and then rise back up as it settled to idle.

I would have expected the vacuum to be higher at lower RPMs. So, not sure what's going on.

Your expectation is correct. That vacuum is too low.

You need to find cause and address.

Usual suspects:
Valves not adjusted correctly (ie too tight)
Intake leaks
Throttle body leaks / wear as Brant suggested
Cam is not stock and is way to aggressive for D-jet to deal with.

[Superhawk996]

However, the throttle does stick just a little bit when cracking it open. Is that a sign of wear? I had assumed that was the plate sealing against the bore.

That is a sign of wear

[BillC]

I did hook up a vacuum gauge. When running at 1400-1600 RPM, the car would idle at 8-10.5 inches of vacuum. Any lower, and the vacuum would drop to to 7-9-ish, and then the vacuum would go toward zero as the car stalled. If I revved it up with the throttle, I could watch the vacuum drop to zero and then rise back up as it settled to idle.

I would have expected the vacuum to be higher at lower RPMs. So, not sure what's going on.

Your expectation is correct. That vacuum is too low.

You need to find cause and address.

Usual suspects:
Valves not adjusted correctly (ie too tight)
Intake leaks
Throttle body leaks / wear as Brant suggested
Cam is not stock and is way to aggressive for D-jet to deal with.

Going to run down your usual suspects with my thoughts and observations, to further discuss and diagnose:

Valves not adjusted correctly (ie too tight) Possible, but I adjusted them less than 50 miles ago, so hoping they haven't gone out of adjustment so quickly. However, they were all a little on the tight side at the start of the adjustment.

Intake leaks I'm leaning against this. D-Jet is essentially a primitive speed-density system, and any intake leaks would raise the idle speed. Since I can make the car stall by just closing the idle bleed screw, I think that shows there are too few (or too small) intake leaks to be causing the high idle.

Throttle body leaks / wear as Brant suggested Also leaning against this, for the same reasons as for the intake leaks above. However, I did order a "new" throttle body from ebay, and I'll either install it or send it off for rebuild and then install it, just to make sure.

Cam is not stock and is way to aggressive for D-jet to deal with. At the moment, I'm leaning toward this. I dug through all the receipts, and found the one for the engine rebuild. Unfortunately, it just says "Camshaft" without any specs.

An overly-aggressive cam would explain the low vacuum at lower RPMs. With the vacuum numbers I saw at low RPMs -- 6-9" Hg -- the engine should have been at much higher RPMs, instead of under 1500.

If I get home early enough tomorrow, I'll try calling them and see if they remember what they put in this engine. But it's been 7 years since the rebuild, so it's a long shot.

In the meantime, what's the easiest way to check the cam specs without disassembling the engine. I'm guessing I can pull a valve cover and put a dial indicator on pushrod-end of the valve rockers. Anyone know the specs of the stock cam?

[emerygt350]

I agree with your assessment. You could measure the movement of the rocker and compare to the known lift of the stock, however, I would check the valve adjustment first while you are in there. How did you adjust them last time? Crusty method or the hard way?

[BillC]

How did you adjust them last time? Crusty method or the hard way?

I did it with the engine on a stand, outside of the car. So I had easy access to everything, and could make sure each cylinder was at TDC when I adjusted those valves.

[emerygt350]

I am a fan of the crusty method. No chance of a mistake. Well, anyway, hopefully you find they are too tight and that fixes it... Otherwise compression testing and if that's ok then it's rocker arm travel measurements. I don't think it would be running well if it was a cam off a tooth.

[Superhawk996]

Pull plugs - betting they are black given how little vacuum you have . Post photos of plugs.

Likewise if you want you can put a mighty vac on the MPS and pull vacuum and and see if that helps allow you to better use the air bleed screw to bring RPMs down without the stalling. Will help narrow down whether it’s the lack of vacuum causing issues or something else.


Those numbers are so low I almost question the vacuum gauge.

[BillC]

Pull plugs - betting they are black given how little vacuum you have . Post photos of plugs.

Likewise if you want you can put a mighty vac on the MPS and pull vacuum and and see if that helps allow you to better use the air bleed screw to bring RPMs down without the stalling. Will help narrow down whether it’s the lack of vacuum causing issues or something else.


Those numbers are so low I almost question the vacuum gauge.

I had pulled a plug the other day, when I replaced the CHT. The center electrode was a medium brown color. Not going to bother pulling any of the other plugs until I get further along with the diagnosis -- the car is definitely running rich when I try to make it idle where it should, so the plugs won't tell us anything new. And, that richness is almost definitely because the vacuum level is so low.

I did hook up my old mityvac to the vacuum gauge I used yesterday, and it turns out the vacuum gauge is toast. The needle stops at 11", and between 0 and 11 it reads about half the mityvac. <sigh> Now I have to get another gauge.... However, even with the bad gauge, we know the vacuum is low -- that needle should have been pegged at the gauge's maximum the whole time the car was idling.

I did call the shop that rebuilt the engine. They actually remembered the PO ("That's a name we haven't heard in a while."), not sure if that's good or bad.... They are going to look up the build information and will give me a call back about the cam.

[emerygt350]

You can just use your mighty vac as a vacuum gauge

[BillC]

I finally heard back from the shop that built the engine. They left a message on my phone that said they put a web-cam 110 in the engine.

I checked WebCam's web site, and didn't find a 110-grind cam under the Type 4 listings. So then I called WebCam, and they confirmed that they don't sell (and never have sold) a 110 grind for the Type 4 engine.

Unfortunately, when I called the shop back, the builder had already left for the weekend. I left a message, but probably won't hear back before Monday.

I did check WebCam's listing for Type 4 cams that come close to the 110 specs, and I'm wondering if they put an 86a cam inside.

Either way, the specs are wrong. An Engle 110 has 31 degrees overlap, a WebCam 110 is 39 degrees, and a WebCam 86a is 35 degrees. Stock cam (according to WebCam's website) is 8 degrees overlap.

I'm guessing the shop that built the engine thought the PO was going to convert to carbs, and/or the PO just didn't know any better.

Unless I get a call back next week with a different cam number, I think we now know why the vacuum is so low at idle.

Now I just need to figure out which way to go. I definitely don't want to downgrade to carbs. I also really don't want to have to replace the cam, since the engine was rebuilt only 300-500 miles ago, and it runs very strong over 2000 RPM. @JamesM has told me some enticing details about going MS3, so I'm waiting to hear back more from him about that option.

If I have a chance this weekend, I'll jack it back up and put a dial indicator on the rockers and directly measure the actual lift, to confirm one way or the other.

[Superhawk996]

Assuming you are correct about the cam - micro/mega squirt it. Way better in the end than carbs.

[emerygt350]

I agree, we are all going to have to go that way eventually.

[Superhawk996]

I agree, we are all going to have to go that way eventually.

I’m afraid you’re correct - especially now that MPS diaphragms are in question.