help with 1.9 bouncy idle

[logans5vw]

Hi all. Need some help or suggestions to fix an idle problem on my 85 1.9 auto
trans westy. Engine idles ok at start-up idling around 1100 rpm when ambient
temps are around 80+ and around 2000 when temps are cooler 60s-70s. The bouncing
starts when after driving on highway and engine is warmed up I put car in park
or neutral then it starts revving up and down between 800 and 2000. It runs
smooth at highway speeds and around town with no surging but at stop lights or
stop & go traffic and my foot on brake I can feel a slight pulsing. Within the
past year I have installed new O2 sensor, temp II sensor, cleaned grounds and
replaced some of the small vacuum hoses and plastic tubing. The plug for the
idle adjustment has never been removed during the past 30 years so it hasn't
been messed with. Should I be looking at the MAF next? Any help or suggestions
would be greatly appreciated.
Spencer
85 westy auto

[morymob]

Chech tps adjustment, manually move throttle, listen 4 tps to open close, u should hear it click, meter sw, closed will show a short, normally makes a ground , open reads no short. U will ger some back resistance thru ecu if when sw is open. This ground is ecu's reference to set idle speed, if u have turned the large screw on afm this does directly effect tps adj. Sometimes if idle is a bit fast u can turn screw ccw to set idle & at same time adj tps sw so it closes, as usual no warranty offered at this time. The plug u mentioned isn't used 4 idle speed adj, hss to do with emissions adj.

[Terry Kay]

Take a look at the TPS (S) and check the adjustment, verify correct operation, then check what kind of vacuum you have at the TB port.
Should read 0 but up to 1 inch is acceptable.
_________________
T.K.

[hdenter]

Have a look at the aux air valve as well. It is located on the right side below the intake runners. It has a hose going to it from the "S" boot and a second hose from it to the plenum. If it sticks open the engine will start and idle great, but as it warms up the idle will bounce like it has a vacuum leak. The test is to warm it up so that the idle bounces and then clam off one of those hoses. If the problem stops when clamped, you have your answer. Usually a good cleaning will cure the problem

Hans
_________________
'79 triple white convertible bug
'84 sunroof vanagon
'85 weekender

[Wildthings]

Sounds like what you are seeing is the ECU cutting off the fuel because your idle is too high. On the 1.9 the cut on and cut off speeds are the same causing the engine to surge. VW fixed this problem on the 2.1 by having a cut off speed that is much higher than the cut on speed. If your throttle shaft bushing are getting sloppy or if you have other vacuum leaks that are leading to an above spec idle speed then this form of surging is common. With a manual tranny is is an absolute PITA.

[logans5vw]

Thanks I'll recheck my vac hoses and the aux air reg. Would a bad boot cause this idle problem? The one on now is the original and has fine cracks on the surface.

[atomatom]

air leaks of any kind will cause this (and i suspect are the most common cause). annoying because if you fix one, it doesn't matter until you fix them all.

s boot, the aux air regulator, the 90o elbow that connects the aux air regulator, the connectors going into the s boot, etc.

i've repaired cracks in my sboot with some black rtv stuff, it won't last forever, but does the job for a bit.
_________________
84 Vanagon Westy, 1.9L, California raised but defected to Canada.

[logans5vw]

Still can't find cause of idle problem- YET.Did the cold & warm S boot to aux air reg hose squeeze test and rpms dropped when cold but not when warm. Top throttle switch clicks when you press the "wing" and reads 0 ohms at rest and inf when pressed. Don't have or have ever used a vacuum gauge. I'm sure it's something that you all have suggested so will follow the Digijet manual tests. Terry do you know of a shop that works on Vanagons? I'm 2 burbs away from you. Thanks all.

[cyclecast]

Ever figure this out? I have the exact same behavior with an 85 westy auto (from colorado).

[logans5vw]

The shop that worked on the van made adjustments to the air flow sensor and the idle speed. That took care of the serious bouncing idle but it is still faintly there. They said I needed a new auxiliary air regulator because idle at start up is now (was) to low. A year later (now) it seems to start up just fine and has a normal idle when cold but I never installed the aux air reg because I couldn't remove bolts holding it on so it sits in a box. Cyclecast make sure you check for any air leaks as atomatom suggest and that your throttle and idle switch is in proper adjustment. Please post any of your findings or fix for this.

[heidi85ho]

Check the timing. Mine was advamced a bit by the shop. When i corrected it back to bentley specs, the idle surge went away. The 1.9 seems to be very sensitive to timing adjustment.
_________________
85 westy-1.9-standard trans, FAS GenV 2.0

[Wildthings]

Most 1.9L engines are going to have a blown retard can on the dizzy at this point in time. This will cause a fast idle which will result in surging. You also can no longer adjust the timing by the book as your timing will be extremely retarded if you do. The best way to set the timing on a 1.9L engine is to set it at 28-32° BTDC at 3500+ rpms, hoses off and plugged. This will give you the correct timing whether the retard can is good or bad.

Again: YOU CAN NOT SET THE TIMING CORRECTLY ACCORDING TO THE BOOK IF THE RETARD CAN IS BAD.

[cyclecast]

Changing the timing (with a voltmeter) fixed this in mine!

More detail on this post.

https://www.thesamba.com/vw/forum/viewtopic.php?p=8477899#8477899

[Wildthings]

[cyclecast]

Yeah...I should get a real timing light. I was a bit worn out from fixing the fuel system, steering, suspension, front brakes, starting and charging issues this spring and summer already. Wanted to just fix it with what I had on hand.

Bad news - it seemed fixed in town, but after stopping at a gas station on the highway, it started back up again. It does seem more precise now Maybe I should order a vacuum can. Kind of running low on funds and spare time at the moment.

Good news, it is much more peppy on the interstate and doesn't have gas smell from exhaust.

[cyclecast]

I should add that idle at start up / cold is on the money around 850 rpm and rock solid.

[Gauche1968]

[cyclecast]

[Wildthings]

[Gauche1968]