odd idle issue

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bmwvwguy
Posts: 21
Joined: Thu Mar 21, 2019 5:20 pm
What year is your cabby?: 1991
Do you own a Cabriolet?: Yes

odd idle issue

Post by bmwvwguy » Sun Aug 04, 2019 12:21 am

91 cab with Digi1. so i went through and reran ALL the vacuum lines properly according to the diagram on cabby-info. before it idled about 1500 and now it idles at about 1000. better but not quite right. if i go any lower it wont stay running. also even at 1000 it seems to have NO power. we adjust the timing and it has some power but it ups the idle to almost 2000. static timing is spot on, checked that 3 times, but if we put it back to about 6*btdc as per Bentley it pops through the intake and wont start. i am at a loss. i need this car for the next few months while i do my diesel swap on my Jetta. BMW is down to a cracked oil pan. just my luck that this thing brakes right now.

any ideas??? oh i also fixed the throttle body as one of the vac ports was broken. so it also got a new TB gasket and idle screw o-ring. so no more vac leaks that i can find.

it could use a new cap and rotor but they cleaned up ok. plugs are good and properly gapped, wires check out good as well. fuel filter is an unknown though. thats the ONE filter i have not changed yet. $$ i dont have right now.

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Briano1234
Whats that smell?
Posts: 4095
Joined: Mon Mar 21, 2005 5:45 am
What year is your cabby?: 1992
Do you own a Cabriolet?: No
Location: Duluth, Ga
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Re: odd idle issue

Post by Briano1234 » Sun Aug 04, 2019 7:37 am

I would do the Static timing as outlined in Ron's tutorial. You set the base time, then use a DVOM to adjust it. Way easier than the way the Bentley states, and it is usually spot on and only requires one person.
https://www.reflectionsandshadows.com/c ... -digi.html

VW's hate vacuum leaks....and you checked the Idle by-pass screw on the back of the throttle body as if you can turn the 7mm screw by-hand then the o-ring is bad and a air leak.

Another place I have seen them do this is at the PVC to Rubber air tube. The air tube can get soft and after years of use can hole under pressure so you may want to check it.

Spark plugs should be changed to NGK, as the engines run better on them. Cabby-info.com has the numbers for the plugs.
You didn't mention if the fuel pumps were whining in the rear and you can hear them over the running car lastly have you done the fuel pressure tests for residual pressure?

Have you replaced the main grounds? Battery to frame and frame to engine/tranny? VW's don't like iffy grounds either, then be sure that the Digifant controller connector is tight.

Sounds more like a air issue or a Fuel flow issue.
Briano

Yes as matter of fact, I have the Luck o'the Irish...everything I touch turns to fertilizer of the bovine variety.
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bmwvwguy
Posts: 21
Joined: Thu Mar 21, 2019 5:20 pm
What year is your cabby?: 1991
Do you own a Cabriolet?: Yes

Re: odd idle issue

Post by bmwvwguy » Mon Aug 05, 2019 1:35 am

All vac lines, t.b. gasket and idle screw oring are new. Ill check the PCV stuff tomorrow. As for plugs, already have NGKs in it and the look good. Regapped them Saturday to be sure. I also cleaned the cap and rotor but will be replacing them when I get paid. In tank fuel pump is making some noise so I'll be looking into that as well. Also doesnt help I ran out of gas yesterday.

Grounds have been cleaned under the airbox and motor. As well as the body panel grounds under hood.

bmwvwguy
Posts: 21
Joined: Thu Mar 21, 2019 5:20 pm
What year is your cabby?: 1991
Do you own a Cabriolet?: Yes

Re: odd idle issue

Post by bmwvwguy » Sat Aug 17, 2019 2:26 pm

I THINK I found at least part of this issue. Distributor died on me last Saturday. And its an intermittent deal to boot. I WILL be replacing it soon as well as re timing the motor to be sure everything is in order.

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