Rough idle/vibration

[CarlosA]

I've been working on my 1979 rabbit with a 1.6 NA engine for a while now. I got it on the road about a month ago and have worked out almost all of its issues. The final mechanical issue i`m dealing with is the vibration at idle. This one is literally driving me crazy, anytime i`m at a stoplight the vibration is so bad my fingers and toes start to go numb.

Obviously these engines shake and whatnot, but compared to my 1978 its night and day.

Here are some of the things i`ve tried, and obviously something is missing from this list that will be a solution... What has worked fro you guys?

• Rebuilt & balanced injectors (two sets tested)
• Changed all motor mounts
• Shimmed the front core mount til snug - no change
• Idle speed set with a digital tach at 894.5 rpm which is slightly high
• Vibration vanishes at 1000 rpm and above
• Checked and tightened every single bolt in the intake/exhaust/IP
• Engine was also rebuilt during the summer compression is flawless
• I`m sure i`m forgetting some little things

Now besides that stuff here are some other details:

Engine had a seized rod on #1, I replaced this and the crank - rebuilding everything else
Car runs and drives great, it has about as much power as I expect with the lower geared ACH 5 spd over the old GC 4 spd
Lately I blamed the entire issue on air in the lines, eventually tracking down and fixing that issue entirely - clear lines everywhere including return, and replaced the in tank pickup screen with new

Final detail ... I can't get the engine adjustment perfect according to bentley no matter what - it seems like it needs to slide back slightly more to be perfectly centered in the mounts, it just wont happen.

Last weekend I feel like the vibe was gone during a 250 mile trip, returning in the last 50 miles or so. This is immediately after changing the last motor mount on the passenger side. Tonight I re-adjusted engine and made sure all bolts were snugged up. No change, maybe slightly worse.

[Rising]

What's the IP pump timing set at? Someone can correct me here cause I'm no expert but I want to say mine felt rough at idle but otherwise fine with slightly retarded timing.

Opening up a can of worms on myself I'd try a little more advance to see if it goes away.

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[CarlosA]

Thanks for response. Running at .95 now after several trips from .87 to 1.05, 1.15 etc. Also no change with cold start advance. 107 AG IP is on my list to dig deeper if no other solution found.

[damac]

I am having an issue like this in my jetta right now.  Everything is the same on this car except I took the turbo out and its injectors/pump.

That setup would idle smoothly even cold(just cackled more).

So I got the injectors, and I will actually try another set that were rebuilt in a couple weeks.  But for me it seems to point at the pump?  This pump used to do its job and was left with some fluid in it while on the shelf.  But it makes me think I should yank it apart and clean it.  That has helped various issues with more than on pump in my experience.

Mine isn't smoking badly or "missing" but I will come to a stop sometimes and the whole engine is out of balance it feels like.  If I rev to slightly above 1000 rpm it seems to smooth out.

[CarlosA]

Yeah same here. ^ I think the pump could use a tear down. I'm 100% sure it's not leaking or sucking air, but never drove this car before the rebuild.

I should add that my car also starts easily - less than a crank hot or cold down to ~ 40 degrees. No trouble there and little smoke, mostly after I retarded it a bit.

[Gizmoman]

I would start by thinking of the bits you changed -

Engine had a seized rod on #1, I replaced this and the crank - rebuilding everything else

.
You sound like you know what you're doing but I thought I'd ask - did you weigh the new rod against the other three? Is there any possibility the new crank is not balanced?

[TylerDurden]

As a relative neophyte, I would imagine an imbalanced bottom would have pronounced harmonic vibration throughout the rpm range, not just at idle.

My Caddy had a lot of vibration in the chassis even after new motor mounts. It was later revealed to have been improperly straightened after a collision.

[CarlosA]

I would start by thinking of the bits you changed -

Engine had a seized rod on #1, I replaced this and the crank - rebuilding everything else

.
You sound like you know what you're doing but I thought I'd ask - did you weigh the new rod against the other three? Is there any possibility the new crank is not balanced?

Yes, but have also found that the balance is pretty far out on stock engines I have disassembled.

My Caddy had a lot of vibration in the chassis even after new motor mounts. It was later revealed to have been improperly straightened after a collision.

I got the title in the mail yesterday and opened it last night to see these big words:

TITLE BRANDS:

TOTALED

RECONSTRUCTED

lol ... maybe that explains the impossible engine alignment!

I`ll measure everything according to the Bentley and see if its something I can deal with.

[CarlosA]

I just drove this car hard for a while, at one point climbing a hill I got some white smoke for a bit, cleared up and got some power back but everything still acts the same. Seriously thinking about pulling the pump and seeing what it looks like inside.

[TylerDurden]

What kind of rpms when the smoke got white?

Have you checked IP internal pressure? AIUI, if it's on the low-end, dynamic timing may not advance as much.

[CarlosA]

I haven`t checked the pressure on this one. The flow is decent, I filled a quart container the other day before bottle feeding it to try and troubleshoot. Didn't take too long, about like my other car/pump.

[CarlosA]

I was just out there feeling around while the engine is idling and really driving myself crazy over this. Here are some findings on a scale of 1-10.

• The engine is a 10/10 for reference
• The front end & bumper vibrates on a 8/10
• The firewall is perhaps a 6/10
• The drivers side inner fender near the mount is probably a 6/10
• Passenger side near the mount slightly less than above
• The steering wheel & pedals are a 8/10
• The shifter knob, doors, windshield, roof (outside), seats, etc are a 3/10 (fairly normal)

The front core support mount has been shimmed 3/4" to make it 100% tight - I don`t know if this is correct, I see that BFI has a thin maybe 3/16" shim available. I will probably unshim this because its not doing anything.

[bbob203]

If I rev to slightly above 1000 rpm it seems to smooth out.

If i set my idle at 1000 rpm totally smooths out for me 850 not smooth vibrates like crazy.

[CarlosA]

If i set my idle at 1000 rpm totally smooths out for me 850 not smooth vibrates like crazy.

Yeah that would totally solve my problem too.

One strange thing I noticed that may point to the pump is... if I rev it manually, slowly moving up to there 1000 rpm should be, it doesnt change at all then spikes to 1000 then drops off even if i`m still holding the lever, anyone know what that is?

[CarlosA]

I went through a special process of adjusting the steering column as well, it actually reduced the vibes a bit. Only odd thing was prying on the steering column to get it within spec also caused the linkage to rub on the clutch pedal, and the shifter linkage to be bound up. Very strange.