75 2.0 just replaced points with new electronic module and new matching coil. 1 week later after getting timing set and idle dialed in suddenly began to mixture and run like it was fouled up. Had set 6 clicks on the rich side on e.c.u. and had added resistance to cht or it would idle fast. But did this cause it to foul? They are not oily or carbon like but seems this indicates the plugs are getting too hot. It so do I need cooler running plugs?

Here is a link to good photos of what to look for!!

Spark Plug Photos

Have you read Paul Anders D-jet info?
At the top of the page under 914 info, other websites, Anders D-jet? Adding resistance to the CHT circuit will fool the circuit into being a little more fuel rich, depending on the amount of resistance being added as to how much richer it will be. Also more effect at lower CHT temps when engine is cold. As the engine warms up, the added resistance has less effect on idle. At least that is what I got from reading it.
To say what the plugs need, one would have to see the plugs, and the plugs should not be changed in heat range just for idle.
Tom

Sounds to me like you "adjusted" it right into poor running. Return it to the base settings, get yourself over to the oft mentioned Paul Anders website and troubleshoot until you find the REAL problem. High idle is NOT properly repaired by fattening up the mixture. Ever.

As for the plug readings, the art/science of reading plugs, often badly misunderstood, went away when they took the lead out of gasoline.

The Cap'n

sorry, forgot the pictures

o.k. so yes, i have both the d-jet bosh manual and have been over the anders site etc etc.

the problem was getting a fast idle down, -
when ecu was set at the middle setting, idle was about 1800.
when trying to adjust idle with idle screw on throttle body, it would decrease but upon getting it to about 1500 rpm then an idle hunting would begin- if ecu adj was moved 2-3 clicks to the rich side, then idle would smooth out- doing this 3x idle was able to hold with no hunting at about 1000-1100 rpm.

it is possible the ECU is just initially on the lean side? everything i have read including the bosch book indicates that a lean idle when warm can cause the hunting.
- AAR is closing off correctly when warm - checked
- timing static at tdc, the 27d-at 3500 rpm right on
- valves recently set by experienced porsche mechanic-
- yes new vacuum hoses and checked all possible vacuum leaks
- vac advance is not connected- left as was from the factory in 75- my throttle body has one vac attachment- for retard as was case for 75.
- if vacuum was the cause of the idle hunt, changing the mix would not correct the problem===
I guess the only way to know if the fuel/air mix setting is where is should be is with the propper equipment- tester??

The inline resistor was added because the CHT was lower than should be when warm-

if i had over corrected it - would it cause the plugs to foul or burn to the grey as in these pictures?
thanks for the input

Cap'n - besides the vac leaks often cited, what else can cause the hunting, could the rebuild Mps cause this? i dont have a vac tester.

the bosch flow chart also indicates the TPS idle contact may be worn(i have a replacement circuit board but have not pulled tps to check wear)

thanks.

Sounds like you have a vacuum leak. You indicated you checked the hoses, but there are other things that can cause vacuum leaks. MPS, plenum, decel valve, etc. On Paul's site on the first page there is a line about vacuum leaks. Click on it, and see what else can cause leaks.
Was the high idle a problem before changing the ignition? If not, I would think back to everything I did while changing that and see if you accidently caused this problem. I don't remember anywhere in Paul's site where he adjusts idle by adding fuel%.
Tom

Tom, had similar thing 4-5 month ago, got valves set and had throttle body taken off , cleaned and put back on, resealed and at that time idle was good at 1000 , drove about 1000 miles, when points went- coil too- replaced the coil and points- as said before, when tuning and setting timing, after that i could not get that smooth idle below 1500 without the richness setting being adjusted. --
so if its vacuum im thinking mps might be- ive checked all hoses and the plenum, t.b., intakes etc. i have no decel valve--

phil

Got the timing right? If so, does the vacuum retard pull it down? The TPS not telling the ECU that it's at idle will definitely cause hunting and poor running at idle.

You have to have the valves adjusted correctly and the timing set to specs before you can go any farther with any diagnosis. If the vacuum retard is weak or not working, or if the throttle butterfly isn't closing fully (allowing a vacuum signal to the retard port), you're not gonna get it to idle properly. If it's not closing, the throttle switch won't read right, either. The plate could be jammed, the TS stopping it from closing, or the spring could be weak, broken, or missing. You need to look at that.

Report back!

The Cap'n

I, I Cap'n !

i believe my vac retard is weak- very weak, butterfly is good- had that cleaned up a few months ago, but still need to pull the TPS - maybe tomorrow.
springs are good.

began missing bad yesterday, is intermittant, so im reinstalling the new plugs, wires, points, rotor etc tomorrow(will take the electronic mod off) and will report back with results(then of course the timing etc).

out

pull the dizz out and disassemble down to the advance plate. then clean all the crap out of it. reassemble with some good silicone grease. make sure the advance plate moves smoothly.

a advance plate that sticks with cause high idle and shit running.

Dr. Phil,
Messix may have something there. When you are replacing the electronic ignition, check that advance plate well.
I know we want to drive, and sometimes just do what it takes to make the car run OK, but the Krusty one is right here. Find the real problem and correect it or it will cause more problems down the road. Sounds like you have some experience, so hang in there and you will get it.
I learned long ago that when we try to improve something, we sometimes make it worse accidently. It can be very fustrating! That's why I asked about how it was running before. Running OK before and now it's not, then something you were doing probably caused the problem or at least brought it to the surface. So you are moving in the right direction by going back to the previous ignition. The electronic should work great, but something in the engine management doesn't like it.

Tom

A quick quesion,

have you vacum test the MPS?
a small crack in the diapham<sp?
will cause weird things when engine gets warm BTDT

and how high can you vacum test up to?
Lbs.

You say that you've checked everything for vac leaks, yet you say you haven't a vac tester?? OK, if that's the way your testing make sure TPS is functioning and the advance plate on dizzzy isn't sticking then disconnect everything from the vac source except the MPS. Now set your idle down to appx 1000rpm. If your still experiencing idle problems get the strater fluid and start spraying (cautiously) around injector seals, throttle body shaft, seal and cold start injector. Then reconnect one item at a time until your idle climbs again and bingo. My gut feeling is the AAR and/or a weak MPS. My 2 cents

I know what you are saying. I have done the process of elimination and spraying the stuff at all possible locations. And I took re advice and invested in a vac unit. Tested the mps today and here is what I found- I connected the vac unit and pulled to 25in hg and it leaked down to 10 in 15 sec.
So what is normal? Should it hold longer? This is a 2 year old. Mps rebuilt by injection. Corp - ecklers(automotion) .
Also replacing the cht as it is not testing as it should.

What are the expected ability of an MPS to hold vac?
And how well, easy should the vac cannister hold when tested. Seemed it was weak.
also when I took out the distributor 2 weeks ago I felt like ithe advance plate was not moving easily- I just put a new one in, maybe too tight- I'll recheck it.

Pw

There's your problem
MPS shouldn't have any leaks, Period
your diaphram is cracked, or something is not sealed anymore.
Too bad it's fairly new rebuild but what's rebuild?maybe diaphram was good then?
it's 40 years old.

You can drive it but boy it(she) doesn't like it.
Have an extra MPS to test?
no leak of course.

But sometimes something else could be wrong with the MPS your using for test
Can (and has,me ) drive you crazy.

This is where the carbs mistake comes in
Yank out F.I. put in carb or carbs

BTW I don't know how to spell diaphram!
my eyes are blurry

Hey Philip,

No one has said it, but the plugs are SO WHITE that the engine is running dangerously lean! I would recommend not driving it until you chase the air leak that is holding the idle up.

Did you hear the rattle of "detonation?" With a magnifying glass take a close look at the inside of the plugs all around the center electrode: If you see small black carbon balls, there has been detonation. BAD!!!!

I have never seen a problem caused by a "hot" ignition box, so I would suggest focusing on the F.I. & intake tract.

Good luck,
Terry