smorris

'82 euro with kjet.
Fires right up on first crank but immediately runs rough or stalls with no throttle response and super low idle. Will not take any throttle input but if stalls will again start up immediately and return to rough low idle. After coaxing for several minutes the car will begin to take some throttle with small backfires heard through air box. As engine warms throttle response increases and car will run fine once warmed up...

Tested termo time switch and replaced due to incorrect reading. Installed new switch and no change..

Other notes: Cleaned fuel tank, Replaced fuel filter, in tank screen and cleared out clogged fuel pump (one closest to filter). This pump is still noisy but seems to be working. Secondary pump in fender used to make noise but none heard now. (Haven't check function of this pump)
Fuel system stays pressurized as it will fire right up with little cranking but almost immediately dies/runs extremely rough...

Any suggestions?

jpitman2

Last time mine did this, and actually stalled after 1/2 mile, I checked the Aux air valve, and it wasnt fully open cold. Drilled out the rivets, froze it in freezer, bent the arm with the spring until it was fully open, then checked that it closed ok when hot. Sealed it back up with some M5 (maybe M6?) bolts, nylocs. Good as gold ever since. Cold start idles 1100-1200rpm briefly before slowly coming down to normal.
Pull the front ingoing hose off, and shine a light in to check how far open the valve is.
jp 83 Euro S AT 55k

The Forgotten On

I have the same issue on my L jet (same warm up system). It is usually attributed to a malfunctioning aux air valve as stated above. If it isn't opening all the way your 928 will be running slightly too rich at warm up and sputter, backfire, be low on power etc.

Do as jpitman2 says and you should be golden

Dave928S

Same symptoms and same issue with the aux air valve on mine. Had some good backfires through the intake ... thorough cleaning and it was fine.

smorris

Thanks for the replies!
So took off the air valve and at ambient temp of 90* (Houston evening temp) the valve was closed what I thought was most of the way...(could see just a bit of space due to the notch in the "slide")

Put it in the freezer and there was no change so i take that it was all the way closed...

At what temp should it be open/closed? Is 85*-90* "cold" enough to have it fully open?

Dave928S

It should be open when it's stone cold, which ups the air going past the air flow plate and raises the idle.

smorris

OK, just pulled it and have it in the freezer.. it was fully closed when i pulled it after warming up the car to test. (Replaced almost all vacuum lines late last night.)
will work with it until it is open at cold engine temp...

smorris

Got to ask...
The long tab that is connected to the Bosch electricalplug is what flexes and moves the plate? is this the "spring" that I will be adjusting?the plate is spring loaded with another small spring tensioned to pull the plate closed by default..

What does the electric connection do? Is it a sensor? Is there a test I should perform to ensure I haven't messed something else up?!?

Thanks for the help, first time tearing into fuel injection issues!

Dave928S

Here's the best tutorial on how the whole KJet system works, which will give you a good understanding of what everything does. Watch the whole thing, but the Auxilliary air valve operation starts at 15.30. The electrical connection is for a winding which warms up the bimetallic strip and closes the valve as the engine warms up. Determining that the aux valve is doing what it should first, will determine what action you should take next.

This will definitely give you a clear understanding of the whole system, which is really not the mystery that everyone thinks it is.

smorris

Firing up the video... thanks!

smorris

An update... Problem solved thanks to rennlist members!

After adjusting the aux air valve to ensure it was open more when cold and still having trouble I moved on to the WUR...

Disassembled it and cleaned it out well, checked function and carefully reassembled.
Fired up the car and PRESTO an immediate idle with good throttle response from cold!

Idle may be a 100 rpm or so high and another check of the aux air valve is in order to ensure that it is closing all the way as it should when warm. Will adjust idle speed after this as well as check the air conditioning air supply (not the right name) operation as soon as my new foot well flap actuator ordered from Roger comes in!

Looking forward testing the cold start/idle and possibly driving it to work in the morning! (Even without AC in Houston TX)

Dave928S

Great to hear

KJet is great when it's working like it should. Sounds like you're on the right track ... checking that every piece of the puzzle is working to spec pays huge dividends.

Just thorough cleaning of everything in the system can give you amazing results ... if you can get a gauge it would be worth checking pressures too.

jwillman

My 79 is doing the same thing after intake refresh and WUR cleaning and oring replacement.

Car starts and barely idles below 400, will not respond to throttle and after about 30-45 seconds stabilizes at ~900 and runs well.

Guess I am taking the aux air valve apart this weekend.

Are folks disassembling to clean or just cleaning through ports?

jpitman2

Its not just a clean if it doesnt fully open when cold - then you need to open it, bend the spring anchor so it does fully open, check that it closes when hot, close it up. There is only air going through, so it shouldnt get very dirty.
jp 83 Euro S AT 55k

jwillman

when I pulled the intake apart for the refresh everything was coated in oil. Would not surprise me to find the same in the aux valve.