Engine won't idle after warmup

[77 Riviera Owner]

I'm having a heck of a time trying to get my 77 bus to idle. When I start it up cold and after innitial warm up it runs great. Once I have gotten the engine a little warmer like when coming off the freeway the engine dies almost instantly after pushing in the clutch and getting off the gas. I can keep it running only by holding on the gas.

I have fixed all the vacum leaks that I can find. It is tuned up well with a new 009 distributor.

I've been told that it could be the EGR valve and when I went to get a new one, the guy behind the counter told me that it surely woule not be the EGR valve, although he had no real advice.

[Miguel Arroyo]

Is the choke working right? When you drive (specially when you take off) is there black smoke comming out of the muffler?

[earthmuffin]

Is it fuel injection?
009?
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[musktchup]

obviously have you tried adjusting the idle screw?
or how about the tension on the accelerator cable? most likely the idle screw.

[Randy in Maine]

Did I read that right?

[Randy in Maine]

Also even before you get a new dizzy, check out the decel valve to make sure it passes the Bentley test. While you have it open to the FI section, do the same with your aux. air valve. It may not be closing completely.

The ususal other stuff also (wires, points, plugs), including the vacuum leak check.

Could also be that the 009 is staying to advanced when you come off the gas. Time it correctly for full advance (30*) at 3000 RPMs with a timing light.

[77 Riviera Owner]

Thanks for all the responses.

Miguel: I don't know if the choke is working right. Is there an actual choke with fuel injection? or is it just some type of start valve? No there is no black smoke.

Earthmuffin: Yes it is fuel injection. I just put the 009 distributor in hoping it would help the problem. And there seems to be no change. Other than the timing holds correctly now.

Musktchup: Yes I've set the idle screw. It doesn't seem to help much. I'll try it again. It seems to work only for a day or so. Can I just put some tension on the throtle cable? That could work, but it seems like it would not be fixing the real problem.

Randy: Yes it is an 009 distributor. I went through bouts with vacuum leaks and a gas smell. I think I've fixed all of the vacuum leaks. The points as well as the distributor are brand new. I did set the timing to 30*. I don't know how to check the decel valve and aux. air valve but I guess I could figure it out.

[mightyart]

Better check that timing, sounds like you fuel mixture is off, do you have a Bentley and a voltmeter? You need to check you temp sender #2 and your cold start valve. It is not a malfunctioning EGR valve, unless the valve or tube are sucking in air.
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[ratwell]

Perhaps you are overheating the engine? Also, what grade of oil are you using?
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[Randy in Maine]

I don't have my Bentley right handy with me so this is coming from memory. The FI system does not tolerate ANY vacuum leaks and will cause the sysmptons you are having.

The first thing I would do would be to:

1) Make sure your fuel hoses and vacuum hoses are new or replaced in the past 6 months. I had a fire in my engine a while ago and new hoses saved the bus. Go here and read up http://www.ratwell.com/technical/VacuumHoses.html Use your gumout carb cleaner with the engine running to find any and double check when hot.

2) There is no choke on a FI engine. That function is controlled by the "cold start valve" with a timer, "the thermotime switch", tht allows for extra fuel to be injected into the air plenum for a short period of time when the engine is cold. That cold start valve could be leaking or not sealing correctly and causing a vacuum leak when it mounts to the air plenum.

3) If you go here you can read up on the components of the FI system http://type2.com/bartnik/ Go to VW Technical articles and scroll down to the FI components and read up on the aux air regulator and the cold start valve. The boot at the end of the aux air valve needs to fit really well with no leaks or replace it.

4) Make sure your EGR valve is properly sealed up if it doesn't work. It has the potential for a huge vacuum leak if it is rusted out our doesn't work or doesn't seal correctly. I can't remember if a 77 is vacuum assist or mechanical assist.

5) Pull off the S boot that connects the air flow meter to the throttle body. Inspect that carefully in a bright light to make sure there are no cracks in it. They start to crack when they get this old, and result in a vacuum leak.

6) Put on the dizzy you took off and make sure it is properly adjusted and timed. Check the vacuum can for any vacuum leaks and make sure it is advancing correctly with your timing light and the tach. THe advance should be nice and smooth.

7) The test for the decel valve is described in the Bentley in the FI section. I can't remember how to do it right off, but it has vacuum for both the fuel pressure regualtor and the power brake booster unit.

If you don't own a Bentely, now is the time. It will pay for itself as you fix this.

Let us know what happens.

[Duncwarw]

A 009 is never the answer.
If you still have the real dizzie, I suggest putting it back in and setting it correctly before proceeding.

They make a nice paper weight.

[orangeeyesore]

i dont know why they told you it couldnt possibly be the egr? that was the first thing that came to mind after reading your post. my egr rusted out where it meets the exhaust and my bus did just what your is doing.
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[Amskeptic]

I have found that many mechanics will steer a customer away from things they do not fully understand. That may be true here, save for the following: the FI buses have no temperature control on the EGR. Usually, if it is allowing exhaust gases to recirculate, the engine will run poorly cold, warm and hot.
To restore your idle when hot, get the engine hot enough to pull its little trick on you, and then test fuel pressure, air leaks at the auxillary air regulator, decel valve, and look behind/underneath all of the vacuum leak points that you already checked to see if anything escaped you. Then see if you can help the idle by pulling off the vacuum hose (plug it) to the fuel pressure regulator. If it helps, you have a lean condition. Try turning the air screw, the big one pointing up slightly diagonally at you, counter-clockwise (count the number of turns so you can restore it) until it looks like it might want to fall out. You are doing this with the hose off the fuel pressure regulator. Do you get signs that it might want to idle as you release the throttle? Check back with us. Return all adjustments to where they were.
Colin
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[musktchup]

My motto is "keep it simple stupid"
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Hip hip horrah, hip hip horrah!

[77 Riviera Owner]

Thanks again for all the comments. I'll work on it this weekend and get back.

Mark

[77 Riviera Owner]

For some reason I'm feeling the urge to follow up on my old posts.

It was a couple of vacuum leaks that I was having a hard time finding. One was the clamp at the oil filler tube. The other was the vacuum line that powers the break booster.

[Wildthings]

Hope you didn't spend 8 1/2 years searching for this problem, while putting up with an bitchy engine.

[77 Riviera Owner]

No, fixed it way back. Interestingly, Ken (the bus company) who found and fixed my last vacuum leaks told me to keep everything stock with regards to electrical/ignition. As have mechanics since. Boy are they right. Fix vacuum leaks, and learn how to use a tach-dwell meter and set the points, and the thing really runs great.