I was searching Brad anders site on drivability, and I found my symptom and cause and solution. But it just dosnt make sense.

from site:

After starting when the engine is cold, the idle doesn't come up while the Aux Air Regulator is open (Aux Air Regulator operation has been verified by checking for draw on intake hose). Idle performance is good once the car is warmed up.


Cold mixture is too lean.
Cold resistance of the cylinder head temperature sensor is too low.

This problem seems to get worse on older cars as the engine wears. There are a couple of solutions. You can "cherry pick" a cylinder head temperature sensor with the highest value you can find, or you can add ballast resistance to the sensor - however, this will affect your mixture across they whole operating range (not recommended). A potential fix is to use a dash-mounted switch to add a ballast resistance to the sensor when cold, then turn it off (shunt it) when hot. I'll update this if I ever find a solution I like!! NEW - another potential solution is to add a spacer to the TS2 sensor to delay the warm-up cycle.


Engine is 2056 D-jet with Rabby 9550. Car is 73 with all matching components, ECU MPS and CHT

I have an AFR gauge that tells me the mps needs adjusted. I have not done this yet. The car would run lean at partial load and wot. I played with it for a while and reasearched the brad anders site. I figured out that if I unplugged the temp sensor on the top of the plenum it ran about 10% richer across the board. I unplugged it and sure enough it ran perfect @ part load and perfect @ WOT AFR is right where I want it lots of power but....

cold startup is horrible. It is pegged at full rich on my narrow band for the first 3-5 min, and idles at below 900 sometimes even stalling if I try to drive off and let go of the throttle. AAR is working perfect but the idle is way to low untill warmed up. once warmed up the car is fine and idles @900 a bit rich but i am OK with this due to my cam choice.

I have turned the knob full lean on the ecu and removed the resistor from the CHT to lean it out, this has no effect on the cold richness and idle problem.

Now I read this about the symptoms of low idle at cold start I thought that I was low idle cause I am full rich at startup, could the symptoms be the same, or do i really need to richen it up even more.

if you really want to go the extra step....
shoot me a PM with your phone number and we can talk

here is my totally crazy idea, tell me NO!

putting a Y connector between the AAR and the cold start valve and then adding an additional AAR so I get twice the air and they will close @ the same time after warmup.

Anybody try this ever??

that 9550 cam is going to give you a rich idle. I haven't found away around it. Once warmed it is less noticeable but if you sit at a stoplight too long it will begin to "load up". when this occurs I usually give it a quick nudge at the accelerator to clear it.

Hmm,

You said this:

I have an AFR gauge that tells me the mps needs adjusted. I have not done this yet. The car would run lean at partial load and wot.


Seem like you are fooling the temp sensor to achieve this first issue.

Are you running a rebuilt MPS?

With the 9950 cam or Web 73 you will get a rich idle. Set the idle speed to 1000-1050 rpms to hide this and the AAR valve should work fine.

What AFR gauge are you using? Using a wideband like a LM1 really will tell you whats going on at partload and WOT for your AFR. You should be running 13something to one at partload.

You guys are making think, damn I thought all that shit was gone. Like Geoff said, the wide band is your friend. What I learned was that when adjusting the MPS is minute adjustments of the screws make huge difference in mixture. A change of say 1/16 of a turn of the WOT screw will change the mixture about 3 heat ranges in your spark plugs.
Maybe Geoff can tell us, how many cars did bosch put injection on and is there a larger AAR?

You have to adjust both inner and outer screws to get this right. As Joe said, 1/16th of a turn can have a huge change lean or rich so its trial by error to do this.
Other Djet cars were the Volvo's P1800, and MB's

How can it possibly not idle higher with the aar open? Rich with a huge vacuum leak like that should always bump up the idle. Shure the aar is plumbed correctly?

yes, the cam is a problem; well known issue with D-jet - but -

go to Radio Shack and buy a dial-variable potentiometer - the old one i use is a GC brand Resistance Wheel - part No. 20-104

after you dial up a satisfactory resistance you can replace that with a fixed resistor

my recollection is that the dial on the D-jet is not of much effect, but I'd have to hunt thru very old notes to give you details.
.

here is everything I saved from really old 914-club BBS - apoligies to Dave Darling & others quoted without attribution


"D-jet WOES

I took the 914 to Chico yesterday for an alignment. It was running very rough below 3-3500 rpms. About 15 miles from Chico it stopped. Cranking the motor just caused gas strong gas smell. I had it towed to the shop I have used. (Zeppelin Motors) They have set-up other cars for time trials and came well recommended. Upon my arrival, they checked it out, changed the plugs to a hotter range and noticed that the fuel pressure valve (drivers side of motor) had unscrewed itself and only was at 18lbs.
> After getting the pressure up to 31 lbs., checking the points, timing vaccum pressure module, etc, I then took it for a 3-4 mile drive. It ran really well at all speeds. On the way back from this drive, it died at
the light, it restarted but would only run at 4-5000 rpm range. When Ireturned to the shop, they took a compression check which was around 90 lbs. (I think the gas had washed down the cylinders, thus the low reading) They kept the car overnight, to adjust the valves, thinking they were to tight. and they were right on, so they checked the heat sensor and the FI points. The sensor was a little off and the FI points were bent. They replaced both. I picked up the car and it starts and runs so so (bucking) until about 3-3500 rpms where it starts running pretty well. It's drivable but not race ready.

……………………………………….. and then I remembered that I had at least one other brain, so I swapped it out and to my surprise, the car idles and runs well. I drove it about 50 miles and up to 100 mph. ………………hmmm.. so it ran o.k. for a little while after they did the repairs.then fell back into it's old problem (have i got that right?)

at this time does it idle o.k.?

and it ran rough, but did not "buck" prior to repairs?

(that pretty much means the cam &/or vacuum is not a culprit)(rough probably was just lean) and the only repair that had any real effect was resetting the fuel pressure to spec, at which point it ran well..

maybe that has something to do with why the guy had that fuel pressure gage attached to it??? maybe he was having same problems? and since the screw was loose, that might indicate he had been fiddling with it.. (well, loose is relative.. I don't ever recall any of these to be so loose that you could turn 'em by hand, so if it backed out on its own, that might indicate a problem internal to the regulator)

first i'd attach a pressure gage & see what's going on there, & if the pressure is still at 28-31, and at all rpm

next thing would be to methodically check all the hose & wire conections & then swap one piece of the injection system at a time & test it each time... ( I had to do that on my own car 2 summers ago, which is one reason I have 2 of everything)(it is a lot of hours, but not difficult)

almost faster solution would be to bolt a set of carbs on it & see if it runs o.k., since that would either isolate the problem to the FI, or it would exonerate the FI ( which is why I swapped into a set of spare carbs not long ago)

my experience has been that bucking or "trailer-hitching" is too much fuel being dumped in, but I am not an expert on FI trouble shooting (my car just started doing this at low rpm's, after running well for 8000 miles, so I am about to go on that quest again..)

now, let's think about why it would run better at high rpm on low fuel pressure/delivery.., which at first seems backwards from it ought to be... i wonder if the injector duration is lower at higher rpm, which might mean less fuel is actually delivered? the cylinders don't get as large an air fill at rpm, so this idea has some potential sense to it; the high fuel presssure is necessary to atomize the spray, so at low rpm it has to be well atomized since the air flow is low, but at high rpm a wimpy stream of fuel would still get dispersed by the faster moving air stream... whereas at low rpm & low pressure the fuel might just wet the port wall & not get into the cylinder at all...which sounds like what happened to you so... what things affect fuel spray duration? the MPS tells the cpu to adjust it based on vacuum, the head sensor tells the cpu to put in more fuel when it is cold. Both cases result in injector duration variations. The points only tell the cpu WHEN (how often) to pulse the injectors which has to do with rpm. The fat external heat sensor is apparently not very important in this setup.

So vacuum, sensor condition (& associated wires), MPS condition (& wires), and the cpu itself are the 3 primary problem possibilities Ignition possibilities are limited. Unless there is something awry in the distributor which causes partial grounding or breaking of an essential signal, I can't think of any other thing to look at there...(but for sure, inspect the ground wire between the breaker plate & body.. these are known to fray &/or break & they are sensitive to engine rpm & vacumm changes, since those cause breaker plate movement & can cause intermittent or rpm related breakdown)

also carefully inspect all the damn' little white wires, especially the ones to the head sensor & mps, since a break in one of thos 30 year old brittle wires is pretty common & can cause thes kinds of problems too. If the head sensor is completely disconnected the car will run rich as hell, and may even idle with the fuel pump shut off, since it says C-O-L-D, like 35 BELOW to the cpu.. so even a frayed wire can create a high resistance that says COLD.

I have also seen bad connections where the wire & spade clip join. The worst sitation here is to have to check every wire from end to end with an ohmmeter...

the brain adjustment is ONLY for fine tuning of idle mixture.. it does not affect any off idle settings.. it should initially be set in the middle of the range & is affected by t he condition of the head sensor resistance.. on most cars, it has become necessary to install an extra resistor in that circuit to richen idle enuf to pass smog, and & on my car, the removal of the resistor tends to cause lean rough idle, even turning the knob to max cannot make up the difference

brains almost never fail, but a quick swap is the way to test the idea

if you have a spare wiring harness, you might try that as a first step in eliminating gremlins.. breaks inside the wrapping are not uncommon

also, if you recall the trouble I had last summer trying to get the other engine running correctly, what i ultimately discovered was that some of the white ground wires that attach as a bunch at the back of the motor were not grounded.. I would look at that location & the wire condition FIRST

the fact that it ran o.k. for just a little while makes me suspect something like loose or broken wires, since it is possible to temporarily & accidently bump them into contact, whislt working on the engine, and then have them shake out of position on the road..remember that the shop had to pull & yank on the wires leading to the head sensor when they replaced it... i seem to recall that either on your current harness or the old one, the spade connector was replaced & if the wire is not tightly contacting the connector in the crimp.. this could cause your whole problem (BTDT)

FUEL INJECTORS: TESTING & CLEANING, & etc

I’ve been doing some workbench engineering relate to D-jet operation due to having assembled a somewhat non-stock 2.0 engine: the motor has new german KS p&c’s w/ nominal Comp Ratio = 7.6,... the Cr measures closer to 8.5 due to the heads having been flycut & head gskts removed. The cam is a WebCam 91H with Eaton hydraulic lifters. The heads were reworked by Mark Stephens (The cam opens later but has more overlap than stock 914..) The engine has very low idle vacuum (5-6”) & only 10-12” @ 2500 cruise. This means the manifold pressure sensor is telling the CPU that the engine is at a wider-than-actual throttle opening and results in a Very rich idle mixture & slightly rich cruise mixture with stock (-019) injectors. The engine is very powerful & revs easily thru 6000, whilst the exhaust & plugs show the classic flufffy black deposits. The engine also “trailer-hitches”(surges) on decelereration with closed throttle, & at very low speeds wit light, steaady throttle.. Normal environment is 2700 or higher altitude, & there are no notable degradations in performance even as high as 7000”.

An ancillary problem was rust in the fuel tank which caused frequent injector fouling despite multiple filters on botyh sides of the pump. Replacement of the tank finaly resolved that problem.

Injectors were changed to (-009) (yellow) units which are standard for the 1.7 motors & common to all VW type 4’s. The engine ran well in this configuration (above curb idle), except at sea levl ,where, in mid-90’ s temperatures audible pinging was noted on acceleration even with 92 octane pump fuel. Injectors were changed again to fatter (-038) units common to the 74 & later 2.0 motors.
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About the hole in the throttle disk. All 2.0 D-jets have it. There are at least 2 sizes (we think). The disk can be mounted either way, ie, with the hole on the high or low side...it doesn't matter. We think it is there to insure the vacuum doesn't get too high when the throttle body shuts? Germans don't do things without a reason! They just didn't tell us why. Other owners have also taped this hole shut in order to get the idle lower. However, there is another "leak" in the throttle body...the idle adjusting screw does not seal off when fully screwed in...the diameter of the end of the screw is smaller than the diameter of the hole in the body. When it is screwed it, there is substantial flow through the idle passage. Try this: remove the TB, screw the idle screw fully in and try to blow through the idle passage (it's easy to do, as it breaks out on the bottom flange). You will find that it is REAL EASY to blow through it! I modified mine...increased the diameter of the end of the idle screw to lower the flow...it helps. Others have plugged the idle passage with tape, putty, etc.

………………………………………………………………………………

First step when you think you have any FI problems: Check your ignition system. Timing, dwell, condition of components, all of it.

What you describe sounds like two problems. First, the oscillation is known as a "lean hunt". Your idle mixture was too lean. Unplugging Temp Sensor I (the intake air temp sensor) richens up the mixture somewhat. I'd suggest plugging the sensor back in and using another method to richen the mixture. First, try the knob on the brain. This is used to change the idle mixture. Clockwise should make it richer. If this doesn't help, back the knob off about 8 clicks or so, then see if increasing the fuel pressure will do the trick. To increase the fuel pressure, you turn the bolt on the end of the fuel pressure regulator (left-rear corner of engine compartment, on a bracket sticking up from the engine tin). Loosen the jam nut first, clockwise to increase pressure. This will make the mixture richer. Note: It's a good idea to have a fuel pressure gauge hooked up when you do this, so you can see how much you're increasing the fuel pressure. Don't overdo it. ( <5 PSI change, at a guess.)

Another method is to increase the resistance in the Temp Sensor II (head temp) circuit. Add a resistor or a potentiometer to the circuit where the sensor connects to the wiring harness. Some- thing on the order of 0-500 ohm, 1 watt will do. When you get the pot dialed to something that lets the engine run nicely, measure the resistance of the pot and substitute a fixed resistor of that value. That's because many potentiometers, when subjected to the heat and vibration found in a 914 engine compartment, will start to get flakey and really throw your mixture out the window. Your other problem sounds like a vaccuum leak. I know you've changed everything, but have you actually checked the components?

Take a look at Kjell Nelin's FI article on Tim's 914 Fan Page, <http://www.estinc.com/porsche>. I think Kjell has tests for practically all the D-jet components.

You shouldn't need to block the hole in the throttle plate. If the screw comes out, it may wind up in your intake valve, or maybe even inside your combustion chamber. You don't want that--really you don't.

Two popular candidates for vacc leaks when you can't find any: Aux Air Regulator and Decel Valve. These can have leaks internal to the components themselves! To check these, find the hoses that connect them to the air cleaner. Remove those hoses from the air cleaner, and check to see if there is any suction on them. The Decel Valve shouldn't have any, except at high revs with the throttle closed. The AAR should have some when the motor is cold, and none when the motor is warmed up. If the AAR is bad, it can be opened up and fixed. Another thought: Are the vacc hoses hooked up correctly? There should be nothing directly connecting the air cleaner to the manifold.

Tim's Fan Page also has a 2.0 vaccuum hose diagram. --DD "

Wow, I was a lot less grumpy back then!!

--DD

I would suggest you test your AAR on the bench.
I have yet to find one that was really clean inside so it could open all the way...

Its simple enough to take out and wash with PB blaster or some other petroleum blast to get all the crud out so the spring can wind up tighter.

Also, if you have changed the displacement and changed the camshaft and have not adjusted the MPS...that is really the solution.

rich

I've been thru this with the same components. Your just gonna chase your tail till you adjust the mps. Period! Once the MPs is perfect, everything else will fall into place. Its really that critical. Now, quit wasting time and adjust it so you can enjoy your new engine at is best.

Joseph, another alternative is to ditch the stock MPS and go MegaSquirt. Now you will have tunable AFR across the board. Been where you're at with a Web73 cam - MS worked for me.

PS: you can hide it so it looks stock.

Good luck