Surging idle, loss of compression.

[Moses]

Are you guys sick of my car yet? I'm getting there.

On my way home driving conservatively, the idle begins to surge. Up and down, finally settling in around 600RPM. At the next light the idle swings up and down and dies. It restarts easily.

The exhaust sounds different. Not dramatic, but different.

Biggest change is a remarkable change of compression. On deceleration, there is a dramatic reduction in the back pressure from the engine - it rolls faster than it should. Much less compression. There is also a slight loss of power on accel.

First thing I checked was the O2 sensor. It is in tight. No super-loud exhaust leaks that I can hear under the car.

This morning I put in an 8 Oz can of Techron on a quarter tank then filled it with 91 octane.

Any ideas?

[Moses]

Is it possible that the Techron dislodges some crud and I have a stuck intake valve?

Anyone?

[Joe Bob]

My engine....which came from the same source....had some mickey mouse plugs that came loose and caused a vacuum leak. They were on the throtle body and they were duct tape.....

[Moses]

Interesting observation:

On a cold or warm start with no throttle it idles well. When you blip the throttle, the wild fluctuations begin until the engine dies.

[Speedster94]

hallo Moses
I am afraid if you dont have a knowing Person working on your car SOON ,you will ask me for another Engine because you f.....
it up .
One day you post how the Car pulls to the Red Line ,the next day you have a Vacuumproblem , than you Dyno it and than the V-ram doesnt work .You proved already that you have a good and durable Engine ( a bad Engine would be kaputt a long Time ago ), and i knew it because it ran perfect when i had it .
But seriously if you dont have somebody looking into the Problems you will destroy the Engine especially in a delicate Problemzone like Mixture/elektronics.
Keep in mind: This is not your Grandfathers Oldsmobile .
harald

[Moses]

Harald,

Come out to California and fix this thing for me!

I have a new mechanic. He is well respected around here.

All of my problems have been due to a poorly prepared transplant.

1) Ruined DME

2) Bone dry CV's

3) WRONG DME

4) Vacuum leaks.

I am so tired of this. In truth, I drive the car pretty gently, nothing like you would at a track.

I hope this is all settled out soon.

-Mark

[Joe Bob]

I beat the crap outta mine.....8^)

Cheer up, it will get solved.

[Speedster94]

hallo Moses
How many Bonus miles you have ???
There is very good Mechanics in the US and i am sure it will be solved
soon . If you need wiring Schematics or anything Euro specific Data let me know . I think you start with the right DME for your Varioram,plug the Vacuumholes ,check all Bolts , Nuts and Wireconnections again and you are back on Track .Except for the DME$$ no big Deal .
Harald

[thabaer]

Originally posted by Moses
Come out to California and fix this thing for me!

I have a shorter trip to make than Harald but won't be there 'til Monday

awHellIdunno...

Your previous uncertainty about the full closed/open throttle makes me wonder about the idle switch. I'm assuming there's some such equivalent, scared my pants off the first time I drove my brother's '91 after being so used to my smooth coasting '79.

The fuel cutoff felt to me like it was substantial enough to make the difference that you are now sensing.


BTW: I'm bringing semi-big lenses w/ chemical and digital bodies, be fun to shoot some fresh digies to post and some 35mm to scan at 6000x4000 for Moses posters

PS: hoo's da new wrench ?

[ischmitz]

Moses,

if I wasn't out of the country I would put my 3.6 to a reliability test and come up to the bay area. But that has to wait until the end of the month.

Regarding your problem here are a few coments:

The DME uses various inputs do drive the engine (fuel amount, spark timing, flapper). Among those are a couple of microswitches that read the accelerator position. One for idle and one for WOT. When the idle switch engages the DME simply cuts fuel while the RPM's are above a certain threshold. Once the RPM's get down the DME goes into idle mode where it uses the idle stabilizer to get air into the engine and starts delivering fuel to hold 800 RPM.

If your throttle linkage setup is out of alignment or the return spring is too weak to pull the throttle lever all the way back to idle the mircoswitch never engages. There is not enough air for then engine because the idle stabilizer is not used and you will see your sympthoms. Fluctuation and hunting idle are the result.

I doubt you would have lost so much compression that it wouldn't slow the car down. That would be a blown motor with more than one cylinder dead. Very unlikely.

Try the following: With the engine off have a helper press and gently release the accelerator while you listen to the microswitch click sound in the engine compartment. Once the accelerator gets released gently you can try and pull the throttle lever back by hand. If you hear the click then your throttle cable or linkage is the problem. A quick fix is to add a second return spring. In the long run you want to get a propper throttle cable (PMS or homemade from a 993 cable). The stock throttle linkage has too much drag for the 964/993 return spring.

See the attached picture of a 964 engine for explanation.



Ingo