73' 1.7 with a standing idle that osillates when at rest. With the auto tranny, car wants to lerch into intersections or just stall on occasion. Checked for vacume leaks-twice. It's now at a shop- their stumped. They also found no vacume leaks. New refurbished MPS, new injectors, all new lines: both air and fuel. Shop owner, who worked on the 411/12 at the dealer-lo those many years ago, recalls a fix for it, but can't remember what it was. I've scoured this forum, the 914 forum and that fantastic 914 D-jet diagnostic web page and have come up empty. Seems like a simple fix....
embarrased
Erik
Oscillating Idle
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Three things to check. You have either a power output problem from the engine or a vacuum problem at the transmission. Thats what causes the lurching. Check the vacuum line to the tranny modulator valve. Also check the o-ring behinde the TB where it seals to the plenum. You also need to modify your PCV valve...do a search on my fixes for this. It causes a lot of this problem. Put a fixed orifice into it. The root of the problem is variable vacum at the MPS. The PCV valve causes a lot of this. Most, if not all, rebuilt/refurbished MPS are improperly adjusted. A fair proportion of them leak. You need to do a vacuum test on the MPS. Any leakage at all means it either has a bad o-ring on the body...easy to fix...or a cracked diaphram. I will be finished with new ones right after I get back from the Philippines.
The surging idle causes surging vacuum at the tranny. One more thing to check. There should be a gold pancake shaped thing at the TB with a vacuum line "t" on it. The tee goes to the plenum...then to the tranny. If that pancake diaphram is leaking...it will cause this. Both the pancake diaphram and the MPS need to be checked with a hand vacuum pump.
I suspect...that if the MPS itself is not leaking, the PCV is the culprit making the idle rise and fall. Once you get the vacuum sorted out with a steady idle.....if the tranny still lurches.....you need to get some steel tubing with metric fittings, a couple of presure gauges....and do the driving test in the Bentley type 3 manual chapter on automatic trannys. What is happening.....is that as the tranny ages.....the oil pump output drops a little. When it does...the modulator valve pressure needs to be readjusted. There is an allen wrench adjustment inside of the modulator valve after you remove the vacuum line. But to do this, you need to plug the pressure gauges into the proper ports on th left side of the tranny. There are about 5 of them. Only two of them are needed. You have to drive and watch the pressure on the gauges. If its too low or too high...simply pull over, turn off the engine...pull the hose off the modulator valve.....and turn the screw a bit in the right direction. Get back in and drive and check the pressure again. You need about two sections of 6 foot each of tubing with the proper fittings swaged onto the end. Pull the back seat out....and remove the screws that hold down the black plate on the body. The pressure fittings behind the tranny are right behind that plate....so you can run the gauges right up between the front seats. Its actually pretty simple. BUT....before you adjust the tranny...you must fix the vacuum problems or you adjustmenst will be way off.
Other areas to check for vacuum leaks....the auxiliary air regulator....the runner boots, the injector seals, the valve covers, the vacuum advance unit...and that strange looking little "T" boot that goes betwen the plenum and the auxiliary air reg valve. If this is a California model, you may also have a little electrical valve with two wires on it....over on the bracket for the MPS. Check the vacuum lines for that. It is the decel valve. If the tranny pressure is slightly low and the modulator needs to be adjusted...the pressur switch on the tranny may be opening and closing that decel valve and causing leaks. Ray
The surging idle causes surging vacuum at the tranny. One more thing to check. There should be a gold pancake shaped thing at the TB with a vacuum line "t" on it. The tee goes to the plenum...then to the tranny. If that pancake diaphram is leaking...it will cause this. Both the pancake diaphram and the MPS need to be checked with a hand vacuum pump.
I suspect...that if the MPS itself is not leaking, the PCV is the culprit making the idle rise and fall. Once you get the vacuum sorted out with a steady idle.....if the tranny still lurches.....you need to get some steel tubing with metric fittings, a couple of presure gauges....and do the driving test in the Bentley type 3 manual chapter on automatic trannys. What is happening.....is that as the tranny ages.....the oil pump output drops a little. When it does...the modulator valve pressure needs to be readjusted. There is an allen wrench adjustment inside of the modulator valve after you remove the vacuum line. But to do this, you need to plug the pressure gauges into the proper ports on th left side of the tranny. There are about 5 of them. Only two of them are needed. You have to drive and watch the pressure on the gauges. If its too low or too high...simply pull over, turn off the engine...pull the hose off the modulator valve.....and turn the screw a bit in the right direction. Get back in and drive and check the pressure again. You need about two sections of 6 foot each of tubing with the proper fittings swaged onto the end. Pull the back seat out....and remove the screws that hold down the black plate on the body. The pressure fittings behind the tranny are right behind that plate....so you can run the gauges right up between the front seats. Its actually pretty simple. BUT....before you adjust the tranny...you must fix the vacuum problems or you adjustmenst will be way off.
Other areas to check for vacuum leaks....the auxiliary air regulator....the runner boots, the injector seals, the valve covers, the vacuum advance unit...and that strange looking little "T" boot that goes betwen the plenum and the auxiliary air reg valve. If this is a California model, you may also have a little electrical valve with two wires on it....over on the bracket for the MPS. Check the vacuum lines for that. It is the decel valve. If the tranny pressure is slightly low and the modulator needs to be adjusted...the pressur switch on the tranny may be opening and closing that decel valve and causing leaks. Ray
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raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Oh...by the way...quit taking your car to the mechanic. There are few if any qualified to work on this thing for you without screwing things up. Just getting it running well is not enough. If you get it runningwell in the wrong way...it can destroy itself. Not ebating on mechanics at all. Its not that you can't find and capable of working on automatics...or on the aircooled engine.....but the combination of D-jet, a unique vacuum system...and a unique layout to this tranny, mean that there is nothing else like it out on the road. Also chances are...90 perecnt of the mechanics you fins who are now willing to take your money and patiebtly work on your VW for you.....are some of those same mechanics who 25 years ago....spent all of their time ripping out injection and installing carbs...and swapping 4 speeds for autos....(cause they thought they were overly complex crap).....instead of learning how to work on them.
Its really not hard to do all of your work yourself. Especially with the resources available here. The bottom line is, you cannot afford to have to replace parts....that you may not even be able to get... by being someone else's guinea pig for learning this car. Ray
Its really not hard to do all of your work yourself. Especially with the resources available here. The bottom line is, you cannot afford to have to replace parts....that you may not even be able to get... by being someone else's guinea pig for learning this car. Ray
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type4org
- Posts: 36
- Joined: Tue Sep 14, 2004 2:07 am
Deceleration valve
Ray,
speaking about the decel valve: Mine is misbehaving right now (I get the "high idle" syndrome that is described in the L-Jetronic troubleshooting guide) so I tried finding the switch on the transmission where the electrical cable from the decel valve is supposed to go. I can't seem to find it. The one switch I found is, I believe, the kick-down.
jens
speaking about the decel valve: Mine is misbehaving right now (I get the "high idle" syndrome that is described in the L-Jetronic troubleshooting guide) so I tried finding the switch on the transmission where the electrical cable from the decel valve is supposed to go. I can't seem to find it. The one switch I found is, I believe, the kick-down.
jens
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Erik H
Damn! I knew i was going to get a lecture. Yes, that's why I'm embarrassed. With the going rate for a parking space in San Francisco at $250 and an actual garage with space to work at $350 a month, respectively, you folks do the math. Sure, I can rebuild a type 1 and 2 with my eyes closed, but try a new animal parallel parked in the street with street sweeping twice a week. I see those shots of the gas tank rebuild and I have yard, garage and general space envy.
As far as the mechanics go, the Bay area has an exceptional array of very honorable VW and Porsche heads. When you dig through shiiisters, of course. Think, Deadhead gearheads.
Until my life stuation changes, this will have to do
still embarrassed,
Erik
As far as the mechanics go, the Bay area has an exceptional array of very honorable VW and Porsche heads. When you dig through shiiisters, of course. Think, Deadhead gearheads.
Until my life stuation changes, this will have to do
still embarrassed,
Erik
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Erik H
Damn! I knew i was going to get a lecture. Yes, that's why I'm embarrassed. With the going rate for a parking space in San Francisco at $250 and an actual garage with space to work at $350 a month, respectively, you folks do the math. Sure, I can rebuild a type 1 and 2 with my eyes closed, but try a new animal parallel parked in the street with street sweeping twice a week. I see those shots of the gas tank rebuild and I have yard, garage and general space envy.
As far as the mechanics go, the Bay area has an exceptional array of very honorable VW and Porsche heads. When you dig through shiiisters, of course. Think, Deadhead gearheads.
Until my life stuation changes, this will have to do
still embarrassed,
Erik
As far as the mechanics go, the Bay area has an exceptional array of very honorable VW and Porsche heads. When you dig through shiiisters, of course. Think, Deadhead gearheads.
Until my life stuation changes, this will have to do
still embarrassed,
Erik
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ubercrap
- Posts: 1394
- Joined: Sun Apr 18, 2004 8:00 pm
Hey, you should come out to the midwest, muuuuuch cheaper. 
You could buy yourself a perfectly decent house for $250-350 a month here. Unless I decide to bail out on it and move to China, I'm in the middle of buying a house with multiple garages and huge shop that's a car nut's dream for not much more than that. OK, so we've got a little shortage of culture I'll give you that 
Okay, okay, a major shortage of culture... 
Still, the tradeoff is worth it for me. Good luck with your car.
You could buy yourself a perfectly decent house for $250-350 a month here. Unless I decide to bail out on it and move to China, I'm in the middle of buying a house with multiple garages and huge shop that's a car nut's dream for not much more than that. OK, so we've got a little shortage of culture I'll give you that Okay, okay, a major shortage of culture... Still, the tradeoff is worth it for me. Good luck with your car.-
raygreenwood
- Posts: 11912
- Joined: Wed Jan 22, 2003 12:01 am
Yep...you have the same problem I have right now....lack of garage space. I udnerstand totally ...especially with the prices in the Bay area. But...I don't believe there are any places with what I would call an exceptional array of mechanics, for working on type 4's in general...much less 411/412. If the mechanics are scratching their head on this one....drive away. They should at least have been able to list the potential variances I just listed and their plan to test them. There are no mysteries in these vehicles. If you know the proper tests to do...you will find the problem....100% of the time. If they don't know the proper tests to do....they are not the mechanics you should let work on this car. Unless...you know them....and they are definitive craftsmen...who are willing not to do anything....until they learn the correct method. Otherwise...I guarantee you, they will screw something up. This is not a learners vehicle. The bug is dirt simple compared to this. Not saying the 411/412 is overly complex...just "complicated".
Which decel valve are you using? The electrical one obviously? They do not always go to the tranny. Some used a vacuum switch that is dome shaped..about 1" in length and diameter. It has a scrw on top, and two wires....gong into the silver decel valve relay. The vacuum line goes to the connection near the auxilary air reg. Ray
Which decel valve are you using? The electrical one obviously? They do not always go to the tranny. Some used a vacuum switch that is dome shaped..about 1" in length and diameter. It has a scrw on top, and two wires....gong into the silver decel valve relay. The vacuum line goes to the connection near the auxilary air reg. Ray