Hello,

I am working on a major resurrection of this 1974 914 2.0L.

I have completed changing /replacing the fuel system (lines, injectors, tank, etc), a major tune up and a reseal.

After a major tune, valve adjustment and timing - the car ran really well. I was very happy.

Started it today - to just hear it run - very rough idle when cold (this is new). It appeared to hunt between 300-700rpm - surge/die/surge/die/surge/die.

I have not touched the idle adjustment on the throttle body - it appeared to run at about 1000rpm when warm yesterday.

Cold Start Valve? AAR? Not sure where to look first. I will check the vacuum hoses again tonight.

Thanks,

Frank

Read Paul Anders "D-Jet Idle Stability" page.

http://members.rennlist.com/pbanders/idle.htm

Should help in troubleshooting

Check the injector clips to be secure...one may appear secure but loose...ask me how I know.

Just a minor correction ptravnic. His first name is Brad, Brad Anders. And yes Frank, that site is the Bible to D-jet owners.

[/quote]
Just a minor correction ptravnic. His first name is Brad, Brad Anders.
[/quote]


DOH! Shame on me for the mixup. Apprec, otherwise I would have kept calling him Paul... For his contribution he should at least get his name correctly credited...

-pt

Actually, his 1st name is Paul, why he goes by his middle name is not known to me

You beat me to it Mueller. Paul "Brad" Anders.
But Paul, Brad, Paul.... Whatever, we won't call him late for dinner, and we'll always call him a D-Jet guru!!

At any rate...
Cold start valve? No.
AAR? Maybe.

did you try adjusting the mixture on the cpu? clockwise richer.. or the screw on the throttle body for higer idle? Maybe check the cyl. head temp sensor to see if it the wire didnt come free while you were tinkering?

I fought a mysterious "Idle Hunting Problem" for weeks (75 2.0)...New hoses, clamps, brake cleaner around all vacumm fittings, checked F.I. connections and injectors, timing, etc...Nothing worked...Every member on this board gave some suggestions, nothing worked...

One day by accident, I unplugged the sensor on the front of throttle body...Hunting stopped immediately and she has run like a dream ever since...

I just left it unplugged...Never has effected performance, starting, running, nada...Plug it back in and it immediately starts to hunt...

It works for me...

2-OH!

Unplugging a sensor probably just caused it to run richer. The original hunting problem suggests a vacuum leak or something causing it to run lean. I would think it would be better to fix the problem by finding the air leak than by artificially richening the mixture.

But the original post mentioned the hunting was happening at 300-700rpm, which is low. So I don't know.

The temp sensor on the plenum will affect the richness. The connector on the throttle body should be the TPS though. There is a Pelican article on adjusting that. The tracks can wear and it could need replacement. Again though, I would fix it before just running with it disconnected.

You're sure the timing is correct?

perhaps temp sensor was unplugged.....but I agree try to find the problem first before going that route. I just got done clamping down all my vacuum lines and it made a big difference.

Hi,

Too many meetings the past few days to get back to the site.

I will definitely recheck hoses for air leaks.

Stupid question - Where is the temp sensor for the heads located? I am not leaving anything to chance.

I did read the D-Jet bible and the AAR valve looks suspect. I live in North Carolina, so the cold start valve would not come into effect in 80 degree+ weather.

I believe I can check resistance and if necessary, check to see if it is stuck open or closed. I may have time tonight after everyone goes to bed.

Thanks everyone for their replies.

Frank

little tiny wire going into the head between #3 & 4 cylinders. i don't think you can see the sensor (easily), its under the tin and a real pain to get to if i remember right...

Correction....The sensor is mounted in the Intake Plenum...Adjusting the rich/lean screw on the ECU made no difference...

2-OH!

A hunting idle with a d-jet system, i had the same problem. the first thing i did was make absolutely sure i had no intake leaks, that helped, but didnt fix it. I then took off the Throttle body and found out that the TPS was worn out so i replaced that.

Also i found that my throttle plate was warped. i replaced those and the hunting went away.

Unplugging that sensor richens the mixture.

If the ECU knob does nothing, I wonder if your TPS is bad - not telling the ECU it's at idle?

Update:

I had time yesterday evening to test a few things.

The AAR valve appears to be working - resistance, drawing a vacuum, closing off.

I had set the timing to 27degrees BTDC @ 3500rpm. Dwell is at 49 degrees.

Found a small vacuum leak under the throttle body where the PVC hose and the small 4mm hose connect. The rubber connector was split - so I sealed that up.

Fired it up - still idled like a dog - surging/hunting at low RPM.

Took it for a test drive - plenty of power throughout the range. After 10 minutes of driving, on the decel, I would get a loud 410 shotgun blast out of the tailpipe. The idle still was horrible. The AAR valve was closed - as it should be.

The timing seems right. The Dwell is in spec. I have adjusted the valves twice - if anything - they were loose. Could it still be a timing problem?

With respect to the Fuel Injection - the car has sat for 14 years. The fuel system was a mess - but I cleaned everything from the tank back, including two new injectors and cleaning the other two. The AAR valve appears to work (but I have another on the way I will swap out). I have not checked the TPS. The cold start valve would not come into play - correct? It is 90 degrees here during the day.

Perhaps the TPS is the next bit - just to be sure. I have not touched the ECU at all.

Any thoughts?

Frank

I had cracks in the airbox under the throttle body on my 2.0. I also had a mismatch of components. The CHT, MPS and ECU need to be the correct (same) year. Do not mix 73 and 74 components.

Did you by chance check to see if the MPS holds vacume? Oh and also the canister on the distributor. If that leaks the car can idle hunt too.

Hi Todd,

I checked it at lunch and the MPS did not hold a vacuum. Have not measured inductance, but if that is true - I assume it is toast.

I have not checked the distributor vacuum diaphram. Any specs on that?

My current status :

The idle screw has no effect on the engine idle speed at all.

I adjusted the TPS according to the PP tech article.

The non-functioning MPS would make it run rich throughout the range - correct?
Would it effect idle?

I definitely get a good backfire on the decel.

Stumped.

Frank

If you pull the MPS hose off while it's running, does it change? If not, the hose or the MPS is completely shot. Pulling the vacuum hose off the MPS will cause it to run full rich. Which at an idle will cause it to drop, stall, and stumble over the super rich mixture.

You need a new or rebuilt MPS if it doesn't hold vacuum. I just replaced a leaky one, and the throttle response is much more smooth and the engine develops full power the way it should.

I did retest the MPS last night and it did not hold any vacuum (O Hg).

I know I need to replace it - but the ultimate question is : Will this impact my ability to idle? In other words, should it still be able to idle at 900-1000 rpm, but just have a rich mixture?

According to the D-Jetronic troubleshooting guide - if the throttle body idle screw does not alter the idle - then it is probably a lean mixture, timing, etc... . So if the MPS is blown - it should be running rich - correct?

Perhaps, I have a compound problem.

Frank

too rich at idle and the engine bogs due to the too rich mix.

Also how is your engine vacuum at idle?

a bad mps will make it run like a dog all the time.
Get a new one.
A blown MPS could and probably will create a pretty big vacuum leak...
So, the car will not idle, nor will it run correct anywhere , at any speed.

Rich

Yup, two prong problem.
1. your MPS is toast (I am sorry to hear that) so your mixture is crap (rich possibly)
2. Now you have a big vacuum leak into your air box after your TB so it leans it out.

Start with the MPS.....come back after that as you will not liekly find/fix anything else with such a major problem looming.

Update - June 15th:

The MPS on my car was blown. I replaced it this evening (thanks Ron) with one that tested to spec. The car's performance improved (no backfire!), but it did not cure the hunting at low idle. Adjusting the idle screw did not affect the idle speed.

Next, I hooked up a vacuum gauge to the throttle body (did not tee it - just blocked off the hose going to the diagphram (retard side) of the distributor. I measured 13.5 inches of vacuum - so that is a little low. Need 15 inches - correct?

However, the car now idled and I could adjust the idle screw, which adjusted the speed to 950 without a problem. It stayed rock steady at 950. Connect the vacuum hose from the dizzy to the throttle body - the car low idle hunts/dies again. Removed and blocked off - 950 rpm.

I take the Mighty Vac this morning - start the car and pull 15Hg of vacuum on the diaphram. The car idles at 950rpm, but I notice there is leakdown to about 5 Hg within 60 seconds. Even after leakdown the car idles. Recoonect the vacuum hose from the throttle body to the retard side of the dizzy - car hunts/dies.

So - is the problem the dizzy or just the Vacuum Diagphram? I will recheck the timing to see if I set static timing correctly at TDC or the 7.5 BTDC mark. Timing was dead on - 27 deg BTDC - but I will double check. and Dwell at 48.

Question: How to test the diaphram? Pull 15HG and see if it holds it for x minutes?

Looks like I still may have a small vacuum leak somewhere else, unless I am measuring it wrong.

So progress. The MPS needed replacing, but the idle is still the same - although no longer burning rich.

Thanks in advance.

Frank

I have a similar problem - was there any resolution with the Dist-Diaphragm?