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Sun Nov 01, 2009 10:37 pm

This is my first FI bus. 1977 2.0. I have other FI cars and have adjusted many a carbed VW.

I am used to the idle on a car being pretty stable. If I set it at 850 and adjust things it will stay around 850. With this 1977 FI bus we have all tested good or new FI parts, the injectors were cleaned by WitchHunter Performance and we chose the best matched 4 of 8 injectors. A cylinder balance test shows equal drops so all cylinders are strong.

At idle with the CO 1.1, the engine hunts. That means it rambles from 850 to 925 rpm up and down. There are no vacuum leaks that I can find. The oil cap is on tight, the PCV works, the valve covers are tight. I have never had a car where the idle is so rambling.

If I rev it a little with no load it will burble and have a tiny bit of misfiring and shakiness between idle and about 2000 rpm. The A/F ratio is constant around 14:1 (CO 1.0 - 1.1 per VW) . The dwell is stable, the timing is stable and not jumpy. Is this just a trait of the L-Jetronic system where it injects each cyl every pulse? I am trying to understand why the idle is not more stable and why the engine runs rougher as it revs up under no load- enough to feel a vibration and the misfire. Under load it is strong and steady. I just think it should be less shaky under no load since everything seems to be correct. I am kinda wondering if this is the issue Ray brought up about the PCV valve causeing unmetered gulps in air - or possibly the EGR opening. I have not been able to find a source for the correct EGR gasket with the small metering hole so it may be that the egr is overcoming the mixture. Any other ideas? Just normal?

Mon Nov 02, 2009 3:53 am

No this is not normal, my FI just idles steady when it has warmed up for a minute. (The first min is a bit rough due to the non stock cam)

Do you mean the auxiliary air regulator by the PCV valve? This does not let in unmetered air. All the air that enters the engine is metered on L-jet except for the air that goes through the AFM bypass canal.

Other then that, I don't know what could be the cause of your problem. I'm not familiar with how the EGR system works and if it could have an effect on the mixture... I blocked my system of.

Did you actually test every single component?

P.S. do you mean this EGR gasket?
http://www.germansupply.com/home/customer/product.php?productid=17181&cat=&page=1

Mon Nov 02, 2009 4:25 am

Likely a vacuum leak at the EGR system and/or idling too lean.

Try sealing off the EGR with duct tape and see if that changes anything.

Mon Nov 02, 2009 6:03 am

You don't have the style of PCV valve that Ray rants about, that is a 411/412, Porsche only valve.

Mon Nov 02, 2009 6:57 am

According to other people's problems posted here, that really sounds like a vacuum leak of Temp sensor II. Have you tested the temp sensor?

Mon Nov 02, 2009 8:01 am

temp sensor II is not in a vacuum area and it is a new sensor. I will pull the EGR off and see if helps.

Mon Nov 02, 2009 8:35 am

I'm not saying the temp sensor has anything to do with vacuum - two different things, but I have heard of both leading to erratic idling. But if yours is new (and properly installed, nice n snug), then skip it.

Mon Nov 02, 2009 12:14 pm

SGKent...my man I follow your posts cause you I and have done so many of the same jobs at about the same time on our buses...

I, like you, have tested and or replaced every sensor/component of my FI. I tested the pump. installed new lines, tested pressure reg, reconditioned injectors, and installed new seals. I'm impeccable about gap, timing and dwell. I have a motor with 135, 135, 135, 140 compression and it still fluctuates a little. "Hunting" is a good term, between 825 and 900RPM. It doesn't roam long...just maybe twice a minute for a couple seconds.

I try to set it so it's at 825 (my bus likes it there) when it's NOT roaming. It's weird cause I've never experienced it with another vehicle, but I've chalked it up to they way my sensors operate. It seems it wants to make an adjustment, then another component tells it...NO! I really think it's normal to some degree cause I have tried like hell to track it down by testing everything and always come up wondering. :shock:

Mon Nov 02, 2009 12:58 pm

Does it 'hunt' regardless of engine temp? Or only when cold or only when hot. This would help eliminate temp sensors being the cause if it always does it from cold start to after a 50 miler

Mon Nov 02, 2009 1:31 pm

Frank79 described it really well.

It does it warm or cold. When it is cold, the first minute or so, it sounds like it is misfiring a tad but I equate that to an uneven placement of fuel from the cold start valve that goes away after a short period.

It drives fine but just doesn't sound right to my ear standing behind it at idle, going up and down in rpm with the cam gear clatter in there. I guess I am also going to need to start a collection of good cam gears. Every one that we bought last year from reputible businesses were worn out except for the new Brazilian one from that clatters now.

Mon Nov 02, 2009 1:33 pm

Sure sounds like a vacuum leak

Mon Nov 02, 2009 2:19 pm

Or perhaps an aux air regulator as it adjusts the little door?

I usually let my bus warm up to about 200º of CHT before I go anywhere. It likes that.

Mon Nov 02, 2009 2:23 pm

Recently I had an aux air regulator failing and I removed it and washed it out with MEK and shop air. Then I lubricated it with silicone spray. Put it all back together and it worked fine. The problem was low idle for me which came from a stuck door.

Mon Nov 02, 2009 2:43 pm

aeromech wrote Quote: Sure sounds like a vacuum leak

I agree with you but haven't a clue where. I've looked at all the usual suspects. Ray Greenwood mentioned the PCV valve causing unstable idle as it allows blowby to escape into the S-Boot. I may try to make some EGR gaskets too with the metering hole since no one ever responded to my search for a source for new or even used ones.

Mon Nov 02, 2009 3:00 pm

Have you tried spraying carb cleaner or ether around the engine while watching for an increase in rpm?

Mon Nov 02, 2009 3:00 pm

I never reached out about my issue cause it really seemed after all I'd been through with my FI manual/Bentley, VOM and pressure gauge, that there was nothing wrong. I get no chattering, but it seems to cough just a little every once in awhile at warm up.

Then it just roams a little a couple times a minute at idle. It fluctuates just like somebody breathed on the accelerator for a second then it recedes to the preset point. Runs like a dream and it's been this way for over two years. I have nothing to compare it to cause when I bought her she sounded like shit, the exhaust was so bad I couldn't really hear a thing.

I did listen to a '78 running in South Carolina at a BP station while on vacation last year. Talked to the dude for awhile and his was doing it too!
He said he never thought twice about it. At the time, this issue was driving me nuts cause I just wanted it perfect.

If you solve it...post it!

Frank

Mon Nov 02, 2009 3:03 pm

I've got the same unsteady idle on my recent FI re-build as you describe. Hunts between 825 and 900 rpm warm. Hunts between 1225 and 1300 rpm cold, always with a nice even change. I've checked every possible vacuum leak spot with starter spray...nothing. Did you use a Webcam 73 ? I'm wondering if it is cam related.

Mon Nov 02, 2009 4:28 pm

Quote: Have you tried spraying carb cleaner or ether around the engine while watching for an increase in rpm?

yes but with propane. No change. Will get some starting fluid today and try again but after reading several other replies it sounds like this idle hunting is a design issue and one to be just lived with.

Mon Nov 02, 2009 4:39 pm

I just tracked down a vacuum leak on my 78 FI 2.0. I tried the propane technique and got no results, by the way. A lot of times when you invert those hand-held propane torches the flame goes out, so when the gas isn't lit, it's hard to tell if it is really doing anything. I found my leak, at the base of the throttle body, by sticking my fingers all over in there, and covering it up - the sucking sound stopped as I fondled the base of the throttle body (sounds so sexy). Mine was a failure of the black plastic seal between the throttle body and air dist box. It too was "roaming" a little bit, but not drastically.

Mon Nov 02, 2009 5:19 pm

You may also check the "door/flap" inside the AFM to see if there is a sticky place in its movement (if there is, hit it with throttle body/carb cleaner). I seem to remember having one that seemed to stick a little when fully closed and that it had an effect on idle or diveability.