Home Technical Discussions Volkswagen Rabbit, Jetta, Scirocco, Convertible: 1975-1984...

Volkswagen Rabbit, Jetta, Scirocco, Convertible: 1975-1984 (A1) 84.5 Scirocco hard start, will not idle


Permlink Replies: 17 - Pages: 1
Last Post: Jan 15, 2014 8:47 PM Last Post By: tcovenant2000
aardvaark

Posts: 54
Registered: 05/14/05
84.5 Scirocco hard start, will not idle
Posted: Jan 7, 2014 5:55 PM
  Click to reply to this thread Reply
My Scirocco has been super-reliable for years, it has always started on the first crank. This new problem developed semi-suddenly and I'm not sure exactly where to start looking for the cause.

Normal behavior is that it would start on the very first crank and go right to 1000 RPM, or a little higher on cold days, until warmed up. Always very steady.

These are the symptoms I noticed, over the course of 4 or 5 days:

1) On a couple of cold starts, it took a couple of cranks to start (a bit unusual), but afterwards ran fine. Subsequent warm starts were still instantaneous on first crank.

2) Once or twice on cold starts, idle would drop to ~500 RPM momentarily and then return to 1000 RPM as normal. Warm starts were still instantaneous.

3) The first obvious trouble happened on a cold start, it took several cranks to catch, started up and then tried to die. I nursed the pedal to keep it running and after a bit, idle smoothed out at ~1200 RPM (typical when cold outside) and then back to normal 1000 RPM when warmed up. On this same trip I noticed the idle was "subdued", maybe just a little less than 1000 RPM. Not enough to see on the tach but enough to notice. The car ran fine otherwise and started instantly when warm.

4) This is the confusing part to me -- the car sits for one day -- and on the next cold start suddenly not only took several cranks to start, but would only idle very rough at ~500 RPM. It would smooth out above ~2000 RPM. The next day it would not idle at all.

5) Since then the problem has stayed the same: 2 or 3 cranks to get it started (cold or warm); it will not idle, but will run at ~2000 RPM. Exhibits low power going uphill, and stumbles on acceleration. As an experiment I closed the idle adjustment screw all the way in, and that way it will keep running at ~1400 RPM, but only with foot on pedal, and rough. It still will not idle at all.

Over the years I've fixed a lot of things on my Rocco but never had to deal with a severe running problem. It's too cold to work on it right now but I did pull and clean the plugs, checked cap and rotor, and looked for obvious vacuum leaks. I'll need to wait for the weekend to dig into it but in the meantime, any pointers would be greatly appreciated!
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 7, 2014 6:10 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
OK. We have to isolate "hard start when cold" from "won't idle or run well when cold".
Start with easy and move to harder. #2 can be done without any tools or even popping the hood, so you might want to do that first.

1. After sitting overnight, pop the hood. Locate the Lambda Temp Sensor (on the flange where upper rad hose meets head). There are three devices there. The Lambda is easy to spot because it has two wires which are on separate, plastic connectors (as opposed to a single connector with two wires). Remove the wires. Use a paper clip to jump the wires by inserting the paper clip into the ends of the wires. Wrap with electrical tape so it can't short to bare metal. Now start the car. Make a note if it starts on first crank. Make a note if it still runs crappy or not. If it now starts easy, or runs well, or both, then the Lambda Temp Sensor is faulty. 10 mins and $20 or less.

2. On a different morning, after sitting overnight, get in the car and insert the key. Turn off the radio and other noise sources. Turn the key to RUN, but not to START. You should hear the fuel pumps running for 3 secs or so, then stopping. If you hear them, continue. Else go to step 3. Turn off the key. Turn to RUN, not START and wait for the pumps to stop again. Do this 4 or 5 times. The purpose here is to determine if you have a residual fuel pressure problem. After cycling between RUN and OFF 4 or 5 times, start the car. Does it vroom on the first try? Does it now run well? Make notes.

3. If you didn't hear pumps running in step 2, you've got a bad fuel pump relay. You can still test residual pressure by NOT starting the car. Jump out the fuel pump relay. Turn the key to RUN, not START and let the fuel pumps run for 15 secs or so. Now turn key to START. Does it now run well? Does it start right away? Make notes.

4. It's possible you simply have a large vacuum leak. Check again.

Let me know what you find.

Thomas
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 7, 2014 6:53 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Thomas, many thanks for your attention. Since the car's been sitting for a couple days in this icebox weather I'll do #2 tonight and #1 tomorrow morning, and report back.

Leo
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 8, 2014 9:46 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Test #2 result: The fuel pumps are audible, and behave as always -- they run for about 1 second when key is turned to RUN. (Typically after the car has been sitting for awhile, the pumps will do a couple of 1 second bursts in a row, but as long as I've had the car I've never heard any longer than about 1 second at a time.) Cycling it 5 times in a row had no impact on starting or running behavior.

Test #1 result: When the disconnected Lambda Temp Sensor wires are jumped, it has no effect on starting or running. The switch checks out ok on the multimeter too -- closed when cold, open when warm.

After messing with the car today I can summarize the symptoms more accurately now:

VERY COLD: I was wrong about taking several cranks to start. It actually will start on the first crank, about like normal when it's cold out, but the pedal must be far down when it catches, or it immediately dies. Will stay running as long as RPMs are above ~2200, but will not idle at all.

WARMING UP: Will stay running at less and less RPMs as it gets warmer.

RUNNING TEMP: Will start instantly and go to idle. Idle is weak and rough. The fastest idle I can get with the idle adjustment screw is ~900 RPM, with random fluctuations up toward 1000. The idle screw is backed out nearly all the way.

With the car fully warmed up I drove it around to check the running. Hesitates on acceleration, has lower power than normal up familiar hills (have to downshift sooner). Doesn't exactly surge or buck but it's far from steady.

Still haven't found any obvious vacuum leaks by visual check but now that it's at least idling and drivable I will get some carb cleaner today and try spraying around the hose connections and intake.

Leo

Edited by: aardvaark on Jan 9, 2014 3:07 PM
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 9, 2014 5:43 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
The next step is to get a dwell meter or duty cycle meter (harbor freight has a meter with duty cycle for $30 or so) and test the Lambda port to see if the lambda circuit is operational. Another thing to do is to idle the car and pop the hood. Stand right by the fuel disty and listen for a buzzing like a hornet. You can also jump the fuel pump relay and turn the key to RUN and listen for the buzzing. Presence of buzzing means your lambda circuit has power. But still need to test the duty cycle. If unsure how, cabbyinfo.com has tons of good info on CIS.
The step after that is to measure fuel pressures. If you're inclined to spend $20 on a shot in the dark, replace the fuel filter. If it's more than a couple of years old it needs replacement anyway. Fuel pressure tests will reveal if there's a problem with pumps or with the mains pressure regulator.
Also, pop the back seat out and listen for the fuel pump operating with relay jumpered and key in RUN position. It should be noticeable, but not loud. No sound or really loud are indicators of in-tank pump problems.

Thomas
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 9, 2014 5:45 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Almost forgot.
The very first thing you ought to do, with the tests you've made already and the symptoms, is to check static timing. Your symptoms are very consistent with a timing belt that has hopped a tooth. Checking static timing is easy. Look in the trans hole and rotate until your crank is at TDC. Pop the upper timing cover off and the dimple on the cam sprocket should be level with the top of the HEAD (not the valve cover). Next pop the disty cap off. The rotor should be slightly CCW of the hash mark on the disty.

Thomas
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 9, 2014 7:09 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Oh man I was hoping you would not say "timing belt". That was in the back of my mind but I thought it wouldn't explain the random fluctuations and gradual onset of symptoms, but rather be a sudden and consistent loss of power.

Wishful thinking I guess, because getting that upper timing belt cover off is going to be an ugly thing. The last time I tried to remove it, the flanged allen head fastener would not come out. It tightens up fine, but trying to loosen it, it gets to a certain point then it sort of goes <pop>, loosen it some more, <pop>, over and over and not coming loose at all. I figured I'd someday end up having to hack the cover off with saw and snips. Ugh. Looks like that day has arrived.

Thomas I really appreciate your advice. You helped me out big time a few years back when I first learned to do the duty cycle check for an emissions test. If you have any tips how to deal with that accursed allen head in the timing belt cover, I'm all ears.

Leo
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 10, 2014 6:00 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
My '81 Black Rabbit, Otto, had the same twist-POP! After asking on several forums I was reduced to snipping and cutting it and then peeling it like a sardine can lid. Wish I had a better answer, but have never heard of one. I got lucky and found another upper cover at the 'yard before I removed it, so had a replacement. That thing was a MO-FO!
I really can['t even remember what was causing the problem. Just remember that once I finally tin-snipped it all away I was able to get the allen head out. The new cover went on without any trouble and I never had any issues after that...which was a good thing. The instructions said to tighten the tensioner until I could turn the belt only 90 degrees. What I didn't get was that it DIDN'T mean to tighten the tensioner until I could BARELY turn the belt 90 degrees...heh...it howled like a coyote and (thank got it was Thanksgiving week, only had to drive to work and back 3 days!) 3 days later, when I went to change it, it had already eaten up 50% of the height of the teeth!
Thomas
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 10, 2014 6:49 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
"Otto" :)

Good to know that bit about the belt tension. I would have done the same thing, going by the instructions in Bentley.

Well to delay the metalwork and suffering I decided to try the Lambda tests first, just in case.

The frequency valve is apparently not working. With pumps running I can hear fuel rushing through the lines but no clearly audible buzz/hum like it usually does. Ran out of daylight so tomorrow I will test the valve's resistance and also see if voltage is present at the plug. I have a spare ECU brain if it comes to that, but I should probably eliminate other causes first.

The transfer pump is humming ok, not too loud.

If the Lambda system is non-functional could that alone be causing the problem?

Leo
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 11, 2014 5:00 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
Something happened today which changes the diagnostic picture.

This is my only car, so of necessity I have been driving it to do crucial errands. Very poor running but with care I am able to more or less stay out of everybody's way. So I am sitting at a stoplight with my foot on the pedal to keep it above 1200 RPM when suddenly I feel it smoooth right out ... and just like that it's back to normal. Idle goes up to ~1500 (since I have the idle screw backed way out), very even and smooth, and vrooom away we go when the light changes green.

I mean the car was instantly back to normal running. Full power, good acceleration, no hesitation, no wobbles. Like the trouble never happened. Joy!!

Anyway daring to hope "maybe I got some bad gas after all" I pull into the grocery store lot and park it. Revved it a few times, nice, nice. All is well. Went inside, it couldn't have been more than 20 minutes, came back out, started the car and no ..... it's back to weak idle and all the rest. BUMMER. I drove around some more in case the slight cool-down at the store was the cause of relapse but it never did recover again.

This is me going WTF?!?!! lol ... The one factor different today is ambient temperature: it's 65 degrees out and it's been 45 or less for the last week since the problem started. But the car was up to running temp long before the miraculous recovery, so not sure how ambient temp would have changed anything.

At least now I can rule out a hopped timing belt. Also -- I think -- it's not a massive vacuum leak, unless the combination of engine temp and 20 degrees warmer ambient temp caused something to heat up enough to swell and suddenly seal. Whatever changed, it was not a gradual improvement, it was instantaneous. And if it's a fuel pressure problem, what would fix itself so suddenly and then revert after being parked for 20 minutes. I just don't know enough about the car's systems to wrap my head around this.

Leo
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 12, 2014 9:38 AM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
I think you're on track. The best thing to do would have been to listen for the frequency valve when it was working well. This does sound electrical. And it will do all kinds of stupid stuff if the lambda system isn't working. There is a "Lambda power supply" which, on the cabbies, is in the spaghetti of wires under the dash by the steering column, or maybe you have to remove the lower column cover. Don't remember 100%. But that's what feeds power to the lambda system.
Before you get too involved, locate the "5th injector" or Cold Start Valve on your manifold. Pass. end of the manifold. Has a braided fuel line running to it. Look at the mounting bolts. There should be 2 or 3 brown wires attached with ring terminals at that point. Pull the bolt, clean the heck out of them. Check them carefully to see if the wire inside has broken, even if the plastic insulation has not. These are the grounds for the Lambda controller as well as the Lambda power supply. Problems here will give you all manner of grief.
If that checks out, I suggest Bentley or Haynes manual for info on testing the Lambda Power supply...though the fact that she ran well indicates the power supply is likely good and there's a connection problem somewhere.
Thomas
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 13, 2014 6:48 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
The grounds at cold-start injector are ok, and now shiny clean. The lambda relay on this car (Wolfsburg edition) is located in the fusebox, on the row above, and one slot right of, the fuel pump relay that sits in slot 2.

I pulled the lambda relay and bench tested it. No continuity from 30 to 87 or 87B when 12v is supplied across 86 and 85. Dead as a doornail. A new relay arrives tomorrow morning. I started the car with the relay pulled and it runs exactly crappily the same, so I'm hoping this will be the fix.

For future reference it's VW part #171 906 381, "no longer available" but a local import shop found it with the Bosch part #0332015006.

Crossing my fingers and praying toward Wolfsburg...
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 13, 2014 6:56 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
Heh...Intermittent relay will certainly do it. FWIW, that relay isn't the "Lambda Power Supply". The Power Supply is a voltage regulator that takes 12V from that relay and drops it to a lower voltage (10V, I think) similar to the gauge regulator in the cluster. The relay is a different beast. My '84.5 cabbie and your '84.5 'rocco are the same vintage fuel system. I have that lambda relay as well. Didn't think to have you check it, so good call! :)
If you're anxious to find out, you could make a jumper with fork or ring terminals and jump the 30 - 87 and 87B...though if you do that, I'd use a fused jumper as 30 is straight from battery with nothing stopping it and one false move could cause all manner of problems.
Probably better to just wait until tomorrow. :)

Thomas
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 13, 2014 7:06 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Yeah I thought about making a jumper and plugging it in, but why indeed court trouble at this point... :)

Most of the existing relays are probably 20+ years old, so in future I'm gonna check them first thing if they seem to have any bearing at all on a problem. If I had the money I'd just go ahead and replace em all tomorrow before they disappear from the marketplace.

Leo
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 14, 2014 7:28 PM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Yea ... fixed! :) :)

I bet that old Lambda relay came to life temporarily in response to much warmer ambient temp in the car on that day. Normally my trips are short and the cabin doesn't really heat up much in cold weather.

The first new relay was marked to be a double-pole, 30 to 87+87B but when plugged in, had no effect. I decided to bench test it just in case, and it was actually mislabeled. Continuity to 87 when powered, continuity to 87b when off.

We ended up substituting a multipurpose 5 pin Bosch relay which works perfectly. The only difference is that it is rated 30 amps instead of 20. It is Bosch part #0332019151.

Thomas thanks MUCH for bearing with me and helping with the detective work. Cheers :)
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 14, 2014 9:09 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
Super glad that was it. In the end you figured it out...I just pointed you in the right direction.
Most people don't have a complete understanding the Lambda system in these cars. The frequency valve's purpose is to rich or lean the mix based on O2 (Lambda) sensor output. The connection people don't make is this: If 50% duty cycle is correct for most situations, then in order to be able to lean the mix, the duty cycle drops and less fuel is fed to the injectors. Stop and think for a moment: If the lambda circuit loses power and the frequency valve isn't operating, would that not be the same as 0% duty cycle? So, maximum leaning out of the mix? On top of this, the Lambda circuit isn't operating, so the output of the O2 sensor, screaming TOO LEAN, TOO LEAN! is going to make any difference and the car, as you've discovered, runs like crap.

Most people assume that loss of the frequency valve means no rich or lean without stopping to think of how it MUST work in order to be able to lean the mix at all. Easier to think in terms of 0 - 100% duty cycle equals 0-100% enrichment, where 50% enrichment is REQUIRED in order to operate normally.

All your symptoms pointed to fuel issues on some level or other. I like it when the fix matches the symptoms.

Thomas
aardvaark

Posts: 54
Registered: 05/14/05
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 15, 2014 12:30 AM   in response to: tcovenant2000 in response to: tcovenant2000
  Click to reply to this thread Reply
Thank you for that clear explanation of the frequency valve. Finally I understand. Bentley should include a similar paragraph in their intro section to CIS-Lambda.

Leo
tcovenant2000

Posts: 1,775
Registered: 12/09/03
Re: 84.5 Scirocco hard start, will not idle
Posted: Jan 15, 2014 8:47 PM   in response to: aardvaark in response to: aardvaark
  Click to reply to this thread Reply
The real crime is Bosch. They designed these systems. I have both books written by Bosch on these systems, one is theory of operation and one is related to troubleshooting emissions problems. Neither of these books, nor VW, nor Bentley, nor anyone (not even "Care and Feeding of your Rabbit for the Compleat Idiot" by Richard Seeley, often considered the Rabbit Bible) mention this. As the result, even VW mechs with years of experience often don't realize this. The only reason I know it is that I forgot to put the grounds on after testing the Cold Start Valve and the car ran like CRAP! That was a complete surprise to me, as disconnecting the O2 puts it into a fixed 50% duty cycle and I somehow expected that no Lambda controller would do the same thing. I was reasoning it out when I realized that, rather than thinking in terms of lower/higher than 50% duty cycle I should be thinking in terms of 0-100% enrichment, thus losing the Lambda would max LEAN out the car.

Yes. I really wish this was the first paragraph of any good Lambda system explanation. :)

Thomas

Point your RSS reader here for a feed of the latest messages in all forums

Popular Discussions:
No popular dicussions.