So firstly id like to say how wonderful this forum is....over the past couple of weeks ive worked through the intake and vacuum system on my 73 1.7 and gradually brought a car with a grotty fuel system that had stood for years back to life....before i get to my main question id like to bullet out what ive done so far.

Replaced tank, pump and all fuel lines and filter

Replaced all plug wires, dizzy cap, points and plugs

Set valves.

Discovered the Eason I couldn’t get the thing to run right was that two injectors (drivers side) weren’t working.

Cleaned injector earth contacts (thanks 914world forum)

No joy, swapped injectors to confirm two were buggered.....replaced all injectors with a good used set.

Fired her up and immediately ran up to 3500rpm. Shut her down, did some reading.

Bit the bullet and bought new gaskets, intake runner boots and all new vacuum lines.

Checked the function of the AAR (works great)

So at this point i have the car static timed, it fires right up but I still cannot get the idle down below 2000RPM.

My big question is “is there any chance there is an electronic issue causing this?”

If I’m back to chasing air leaks the only thing that i can think of that i have not replaced are the rubber rings on the noses of the injectors....if there is a leak here will it cause a fast idle?

I think I’m typing this more for moral support than anything else. Ive read through so many fast idle threads that I’m hesitant to write another one but I’m at the point of giving up.

The only other thing i cant place is a loose wire (black with purple bands) and spade connector that is hanging some where beneath the ECU but i cant see anywhere it may have come from.....any chance this is my issue? Anybody know what that colored wire relates too...ive been searching for an engine wiring diagram but couldn’t find one with a key to colors and components...

Thanks for letting me ramble on

Felix

Possibly the heater fan wires.
I need a bit more info, you must know about the idle bypass screw and some ECUs have a potentiometer to adjust idle mixture.
Fill in the blanks we'll help.

do the FI components match model year?

As far as i can tell they’re original (referencing photos and diagrams everything seems to be as you would expect to find on a 73 1.7) that said I haven’t taken the whole thing apart and checked serial numbers.

I wound the idle screw on the throttle body all the way in clockwise and then backed it out just a tiny bit. I set the potentiometer knob to the factory, middle of the road indent.

Dwell is set to 48 degrees

If i plug off the AAR the car idles at around 1000-1200 but then stalls out...

Only other loose line i have is one of the lines that comes from the charcoal canister (plastic tubes from front of car). From all the diagrams it looks as though its supposed to go to the air box but I’m missing a fitting to connect it...other one of those lines is attached to fan shroud....could this have an effect?

F

Model year '72 and '73 1.7s are identical.
The hoses from the charcoal canister run from the fan housing through the canister to the air filter housing. Do you have a paper filter or oil bath ?

Paper filter.

Is there any way the Decel Valve could be passing air through to the AAR port...does the diaphragm ever break? In effect allowing the AAR port to suck more air?

I'm definitely no expert when it comes to Djet, but here's a couple things to ponder:

You said when you start it up, you can't get it to idle below 2000 rpm. How long did you let it run at 2000 rpm? Time enough for the AAR to warm up internally and close off? These cars initially run up a bit to warm things up, then the AAR closes off, and the idle can drop down to 900 rpm or so.

If it's idling that high even once it's had a chance to warm up, there's a leak to track down.

The car will run without the Decel valve installed. The '70-'71 cars didn't have them at all. You said the car will idle at 1000 then die if the AAR is plugged. Take the Decel valve out of the loop for testing purposes - less potential leaks for now.

Some say the Decel valve is not needed at all, and is actually an early emissions device. Others defend it's use because of how it reduces the vacuum load on the MPS when coming off heavy throttle.

The AAR makes the car idle high until it (the AAR) warms up inside, then it closes off. The reason your car dies if the AAR is plugged is that the engine is not yet warmed up, and is expecting a high idle to get it warm. Once it's (the engine) is warmed up, the AAR takes itself out of the equation. If it's dying once warm, I'm guessing the idle screw needs to let a little more air in at this point.

My car came to me with a single carb set-up, and with the expertise of this board, I sourced and returned my car to factory fuel injection. When I first started it up, it ran immediately up to 3500-4000 rpm. I tightened the intake runners down properly at the heads, and the idle dropped down to where it should. You're on the right track, looking for vacuum leaks.

Others will chime in, and probably correct something I've misstated, so take my ramblings with a grain of salt! As you've seen, this is a very supportive and helpful group.

This is just the kind of discussion i’m Looking for. 2000 RPM still feels a little high for warm up to me. The car has a knackered Monza exhaust though so perhaps the extra noise from that is making me feel self conscious about how high the revs are and leaving it to run long enough for the AAR to close...would love to hear from others on that point.

Taking the Decel valve out of the equation is easy enough to try. I’ll fiddle with that tomorrow.

If you think you have a vacuum leak, I got something for you....

I had the same problem with my L-Jet. But the L-Jet won't idle with a leak. Anyway, check YouTube for a vacuum leak detector or smoke machine.

I made one using a fresh paint can and a few fittings to connect a compressor. Light some charcoal, throw in some cardboard and close it up. attach the compressor to the can and a hose to your car's FI hosing. Also include an inline regulator to keep the pressure down. YOU WILL FIND THE LEAK. I found big leaks, and small leaks. Even my distributor was puffing. My big leak was the connecting point for the throttle body.

BTW the engine should not be running. Check everywhere for smoke. even the valve covers, so look under.

Good Luck.

You can do the same with the AAR. Remove it, Plug up all the hoses and run the car.

If you take it off, it is easy to test. I have a 12v drill, and just use alligator clips on the battery to power it up and see what happens. You can then put it in the freezer and see what it does.

Do you have a vacuum pump? Try to see if the vacuum advance holds. I chased a leak for weeks. Turned out to be one side of the advance. Oh BTW time the engine the way the manual says. Static is not timed that I am aware of. I thought I remembered holding the idle up around 3k rpms and checking/setting the timing on my 1.7. Been many years since then.

You know what mate, i had the same ‘middle of the night staring at the ceiling unable to sleep’ type thought about timing. I realized that perhaps it’ll settle down a little if i time it correctly...at the very least i need to finish the timing process before i go any further....my gut tells me it’ll pick up revs but we’lkl Soon see...first thing I’m gonna do today.

That’s an interesting thought on advance. And i do have a vacuum pump. Is it just a case of attaching the pump to either vacuum port on the distributor? Or should it be a specific port? Its the first car ive ever worked on with two vacuum hoses coming off the distributor.

F

Interesting! I may give that a go......though the idea of discovering small leaks all over the engine is terrifying!!!!

Cap off the hoses to the deaccl valve, it does nothing for your engine.
To check for air leaks use ether or "starting fluid " spray it at hose junctions, increase in rpms will indicate air leak.

Incorrect timing might cause high idle.

I found my video. Not a how-to make the machine, but showing how I found the leak. let me know and I will help with making the gizmo.

I think it is a great tool to check for leaks a couple times a year.

https://youtu.be/rBT1FP131Kw?list=UUO3vjQof5GNgmlTh404OyNA


https://www.youtube.com/watch?v=rBT1FP131Kw

That’s great man! If i cant solve the problem with timing and idle screw adjustment that will be my next project......

Does anybody know what effect a small air leak at the injector will do? I dont know that I have an issue there but I didn’t replace the rubber seals when i swapped in the injectors.

Big place for leaks, cheap fix...

Does it cause a high idle in the same way that leaks in the plenum do?

Exactly...

Any place air can leak is a thing to deal with. Start from the heads and work your way back. There are two seals on the injectors. Follow upstream from there. Look at every potential point a weak seal could let air in. The phenolic blocks, the airbox (which can have cracks around the reinforcing tubes), plenum, throttle body flapper... Carefully examine any place where air can be introduced... from seals to the AAR.

If all of that is truly good, then advanced timing can be a factor... BUT 2k idle on Djet surely points to a big air leak somewhere in the chain.

Replace the small o rings on the injector. That's the only seal. The big one is not a seal. It just holds the injector in place.

You mention the "pot" on the ECU was set mid way, the factory burned a spot into the plastic ring, the dash should line up with that spot, that would be the correct idle "CO" content adjustment.
Look for that spot and adjust your air screw for the correct idle rpm.

Yep, its the factory burned spot that its set to, about mid way.

Just read through this thread.

You may very well have a vacuum leak, but I'd get the timing set perfectly before I did anything else as it can affect your idle. Static timing allows you to get the engine started so you can time it properly.

With my D-jet, it idles the best with the knob on the ECU set to "full rich." A rich mixture lowers idle, lean raises it.

Keep fighting through this - you'll find it!

Any work done to the engine?
Cam, displacement increase, head work???
Is the MPS sealed with rivets or screws???
Need to check the ECU part number, not sure about '71 but I know '70 doesn't have the "pot", you should check your part numbers against the pbanders pages on the rennlist site.

Sticking throttle
sticking aux air valve
vacuum line off or misrouted
intake runners loose
decal valve sticking

That is about it, hi idle is caused by leanness if not a stuck throttle

Other than an aftermarket exhaust I don’t think there are any performance mods. I had it running fairly well yesterday apart from it running on a little after letting off the throttle...figured I was getting close. I then took the rusty and broken Monza style exhaust off and replaced it with a glass pack style exhaust I have and now it runs like shit again......

MPS is held together with screws. Is this something I should check?

I’m gonna do a smoke test after a buddy told me about a trick with a cheap cigar and a vacuum cleaner....stay tuned!

Ive been through all of that stuff, checking function and replacing with new parts. Full vacuum hose kit from AA...thanks for that!

Gonna go back to basics and do a smoke test next.

when you see the smoke coming out of the wrong place, you will slap yourself in the head and always do the smoke test first.

My fast idle was discovered after someone else shared their own "doh!" moment and I found I had done the same thing. When I replaced the throttle body, one if the washers wound up beneath the throttle body rather than on top. You can test by spraying some carb cleaner around the area while engine running and see if idle changes.

Factory MPS should have rivets, screws mean the unit has been rebuilt.
Not really bad, but you should check it for vacuum.

Agreed

with others that your timing & valves need a proper setting before anything else. Next remove and cap every vacuum item except the MPS. It will run fine w/o all of that other stuff. At this point your idle should have dropped down considerably. Now, re-connect one item at a time until the idle jumps up at which time you will know the culprit. The smoke test will also nail it.

I had this exact issue with my D-jet 2.0 when I first got my car 9 years ago-
and all the above apply
I had vac leaks all over- intakes, plenum, aar, etc etc etc. - but after setting timing and valves etc I could not get idle lower than 1500 rpm, it started at about 2800 and got better as I eliminated all the vac leaks - once in installed a AF meter I could see that my MPS was making it very very lean, and that will make your idle faster too.
I had to retune the MPS, which I did with one I rebuilt - I had one that was set to exact factory specs with LCR meter , in fact ive had 2 , and both caused high idle and ran lean., - once I was able to get the MPS tuned more rich ( lets say a 12.8 not 14.8) I then had a normal warm idle.
- also agree with a member about the injector seals- I just ordered some and they were smaller than what I already had and I can see that they will not seal if I use them so check this as a source of the leak with your smoke test(or spray a mist of water it will change idle if it is leaking and can suck in the water vapor)
now maybe yours is fine and you just have fix all the vac leaks and timing/valves. if car is running 20 minutes and its warm and the AAR is closed and now it wants to die you may have to open the idle screw a bit - does it surge up and down? if it does, its a vac leak and its lean - the idle mix screw on the ECU will not work btw if the TPS is not set correctly, the circuit will not activate-

Good Luck!

OK, I’m back at this now, long story but the fuel pump died and while i was trouble shooting that the car fell off it chocked wheels and crashed into the corner of my driveway wall (I Know I know lesson learnt pay attention to safety event when its been your mantra since your dad beat it into you as a teen). Fuel pump fixed, mismatched yellow door and now we’re back to the idle problem.

Sooo, i changed the injector seals, tore the whole intake down again and resealed and checked everything. i performed a smoke test, could not spot any leaks. Car fires up on all four cylinders but races to between 2000 and 2500 rpm, sits at that speed for a minute or so then drops down to an idle somewhere south of of 1000RPM. BUT...if i touch the gas only slightly it races back up to 2500 rpm and then tries to die before sitting back below 1000RPM. The slightest bit of gas makes it race away....

Any ideas?

My '73 1.7 dJet idled fast. I found that my idle adjustment screw WAS my air leak. I had been turning out to reduce the idle. Once I screwed it back in, my air leak was solved and my idle was reduced to "normal".

""That is about it, hi idle is caused by leanness if not a stuck throttle""

I mentioned this also back in February, but both a fast idle and a hunting idle is almost always(once leaks are plugged) is a lean running condition-

I have use 5-6 different MPS on my car and I have had to retune the rebuilt ones that were set back to factory spec because they were set too lean, and yes timing and advance will effect this some as well, but if you read Anders information about the MPS, and if you can get a good one that has been rebuild and is sealed properly and has a good diaphragm, the epoxy plug removed, you can slowly adjust the part and full load mix- get a A/F meter and then you will know hwere you are at or just slowly adjust this until the idle comes down close to 900-1100. If you have the AF meter you will then know where your mix is at when cruising and full load, you might be fine at idle but running lean at part or full load and that will cause increased head temps etc.

- leaks, timing , MPS tune -

Phil

Thanks Phil

The issue i have now is not really a high idle, its the fact that itll idle at just under 1000rpm and as soon as i touch the gas it races back to 2500 rpm for a few seconds and then returns to idle....would a faulty MPS cause this?

No, but the ecu knob turned full clockwise will!

Check that the advance mechanism in the distributor functions smoothly and does not stick. If it sticks advanced, it will keep your idle too high.

How is the timing, anyway?

Other things to consider: You can have a leak through a component like the Decel Valve or the AAR. Those won't show up on smoke tests, but they will show up if you try to blow through the part.

--DD

agreed, and maybe sticky butterfly valve maybe?

I went through exactly what the OP is going through a few years back with a 72 1.7. I replaced every seal, replaced all the hoses, cleaned every contact, bought rebuilt injectors, soaked my AAR in WD40, etc etc. Nothing got my idle down until I discovered my advance plates in the dizzy were sticking. Cleaned them up and the car drove beautifully after that.

At least since you've thrown the whole kitchen sink at it by this point, when you do finally find the actual issue, you'll be set with a great driving car for years to come!

Sticky advance plates in the dizzy will advance idle a little bit. Because they don't retard and thus drop the idle.

The OP stated that idle goes up to 2500rpm.

Let me restate loud and clear: Timing alone can not be the sole problem. Take a healthy car, advance the timing until it races... how high idle can you get with timing alone before it causes other problems? Not THAT much. There HAS to be a huge air leak somewhere below the butterfly in the throttle body.

This sure seems like a perfect candidate for a new 123 distributor. Rule out a whole bunch, eliminate trigger points, advance plates, yada yada, and get a major upgrade all at the same time. Keep the old dizzy/points in the trunk as spares. Do that and prove me wrong! Or enjoy the upgrade and keep chasing the air leaks.

Not trying to argue, but I don't think the OP is idling at 2500rpm. Unless I'm misunderstanding what he's saying, his idle is now fine, but it gets stuck at 2500 for a few seconds when he blips the throttle.

Lubed up the advance mechanism so we’ll see if that helps. Its still racing away when I touch the gas. I just did a fuel pressure test and it’s only getting 20psi when I believe it should be 28psi. Any chance this could be the cause of the stumbling idle then racing away when the throttle is touched?

If the advance plates are really the problem, it's going to take a deeper cleaning to get 30 years of sticky gunk out of the picture. Then lube it up fresh. Be careful while you're in there, because that little braided ground strap between the plates is VERY important.

I notice you keep asking things after they have been talked about. You should report your results after each effort so we know what worked and what didn't. Otherwise it's tough to follow your troubleshooting steps.

That’s exactly what I’m saying. Through the course of this thread ive gone from a motor that was missing on several cylinders and would run no lower than 2500 RPM to a motor that is firing well, will idle just below 1000rpm and has no air leaks. I have set the valves, set the dwell, set the points gap and set the timing. My issue now is that if i touch the gas even slightly it races up to 2500 RPM, stays there for a moment and then returns to idle. Its not safe to drive like this because you are, in effect, driving with a dragging throttle....staying open even after you take your foot off the gas.

I carefully cleaned and lubed the advance mechanism in the dizzy but i doubt it was that....the plates just seamed a little dry and oxidized but still moved freely, i just lubed them as a matter of course as it was not something i had previously looked at.

At this point the only non electronic thing that i have discovered is a fuel pressure of only 20psi. I’m not sure why that would result in the engine racing with only the smallest amount of throttle. I adjusted the fuel pressure regulator but could not get it above 20psi so ill be replacing the pump as a matter of course.

Would love to hear from anybody who has had a similar problem of throttle racing away...

I appreciate all the help here guys. If I haven’t replied to each reply its because quite a few are offering the same advice and its stuff i sorted out much earlier in the thread. From the start ive tried to keep each fix documented and then move onto the next problem. Its been a fascinating journey. With each little fix it gets a little bit better...sometimes its gotten worse...and then ill try again with a little more care, fix the issue and move on to the next thing in the chain. This car had not run for many years and had a fully gunned up fuel system. I can smell victory is near, no matter how many times i walk away from it threatening to sell it as a ‘project’.

My 2 cents worth:
1) Check the vacuum advance and retard diaphrams on the distributor to see if they each hold vacuum with a vacuum pump. If not, the vacuum advance unit needs to be replaced because it is leaking vacuum.
2) you said you sprayed wd-40 into the dizzy to free up the advance plates. You really have to remove the dizzy from the engine take the advance plates out of the diszy and thoroughly degrease them. After 45 yesrs the factory grease has become hard. When you put them backi in the dizzy make sure the screw holding down the points is not so long it makes the advance plate bind and get stuck.

3)Check your throttle cable and make sure it moves freely in and out. Also make sure the throtle return spring is strong enough to close the throttle plate.

4) I was chasing vacuum leaks w/o any success until I took off the auxiliary air regulator valve and tested it per the Brad Anders site. Turns out it was not closing off completely after the dngine was hot, thereby resulting in a huge source of “phantom” air entering the engine and making it impossible to slow down the idle when the engine reached operating temp. It ran ok when cold, but the idle jumped all over the place when hot . Had to completely remove it and plug all hose connections because it was carboned up inside and the aar valve would not move inside of it.

My engine now runs great once I did all of these things.

Now that you mention it, i assumed the throttle return spring was strong enough because there are two on there....BUT...that could also mean that someone screwed around with it in the past and neither are original and both are sub par. Ill check that and physically shut the throttle off at the throttle body rather than relying on the spring. However the revs race away with only the slightest touch of throttle so i doubt its got anything to do with how fast its closing.

I’ll double check everything else. Checking the function of the AAR was one of the first things i did, works perfectly.

Turn the ecu knob ccw a few clicks, then blip the throttle to about 3k rpm and let it come back down. If it is better, continue this step a few clicks at a time till it comes down immediately.