F.I. engine idle goes up and down.. up and down.. up and..

Rex Surewood · Post by **Rex Surewood** » Mon Jun 12, 2006 2:28 pm

You get the idea.. When the engine has warmed up good it sometimes can't get a steady idle.. It runs perfectly until it suddently feels like it's dying - and then picks up again half a second later. This goes on and on and on... When I rev it up and drive nothing is wrong.
This is an intermittent thing.. Some days it goes just fine and the next it's back..

Any ideas?

Post by **Marc** » Mon Jun 12, 2006 3:05 pm

Likely that the idle mixture is a little lean. An induction leak can cause this so check any hoses that go to the intake tract. I suppose your auxiliary air regulator might be gummed up and not closing fully when warm sometimes, too (next time it's surging, pull off the hose to the AAR from the aircleaner and put your finger over the hole to see if the idle stabilizes). How's the throttle shaft play, could it be sucking air in there?

raygreenwood · Post by **raygreenwood** » Tue Jun 13, 2006 6:52 am

Everything Marc listed.....and a couple more. Check the CHT reading when both cold and hot. What is actually happening is that you are most probably rich. This exact performance is common on D-jet when you have (as Marc noted) vacuum leaks. This causes enrichment from the MPS.

The submarining idle and nearly stalling is the engine trying to ingest the excessive fuel with no tenough air. Other things that can cause this are teh CHT leaving you in too rich of a state and teh fuel pressure being too high. Ray

Rex Surewood · Post by **Rex Surewood** » Tue Jun 13, 2006 8:51 am

Thanks guys, I'll start from there!

Rex Surewood · Post by **Rex Surewood** » Wed Jun 14, 2006 2:49 pm

Problem solved perhaps?

I always thought the idle speed was a bit high, so after checking for leaks and clogged AAR i adjusted the idle down to specs, and it became steady as a rock. I drove it a good couple of miles and it never missed a beat..

Hopefully that's the last of it.. Thanks again!

raygreenwood · Post by **raygreenwood** » Wed Jun 14, 2006 3:21 pm

...and of course...it can be that simple! Its worth it to remember that the idle...and vacuum leaks....on D-jet....cause the reverse of what it does on the carburetted car. Any extra ingestion of air causes the MPS to vent. That gives enrichment because it masquerades as a throttle movement . Ray

Eva65 · Post by **Eva65** » Sat Sep 06, 2008 3:57 pm

Every since I first got my "68" FI Squareback (about five months ago) I've experienced a problem with it "surging" at idle during warm up. It was never really bad & since I had no idea what to do about it I just worked on other things. After all, once it was warmed up the problem went away.

Fast forward to last week-end when I pulled the motor. After the motor was back in the "surging" was worse than ever...!! It was so bad that I could no longer pretend that it wasn't there.

The Bentleys said that the caused was... "hose between auxiliary air regulator and air intake distributor detached". I knew the hose was on there & I knew the hose was new but I fiddled with it anyway & found that it didn't fit all that snuggly on the nipple ( HeHe...!! I said nipple ) so I put some hose clamps on it. It didn't completely solve the problem but the "surge" lessened. But now the idle sped was really high. I lowered the idle speed & now no more "surging". I love the few times I can figure out something on my own.

raygreenwood · Post by **raygreenwood** » Mon Sep 08, 2008 5:04 am

Also bear in mind that the plenum or coke bottle shaped manifold has a gasketed plate in the back underneath. In about 100% of all acras this gasket rots away.
The range of potential vacuum leaks on D-jet is huge.
Runner boots, injector seals, auxiliary air reg., all vacuum hoses, worn throttle plate, pushrod tube seals, vacuum advance cans, modulator valve on automatic transmissions.....
Every single leak on D-jet must be sealed. No vacuum leaks allowed. Ray

Eva65 · Post by **Eva65** » Tue Sep 09, 2008 7:57 pm

So how are you checking for leaks? I have all new hoses so I'm guessing that they are cool. I used "quick start" spray to check for leaks around the "coke bottle" & injectors with no reaction. The motor seems to be in good shape. Runs great.

But this morning the "up & down" thing was back again in (when it was cooler) but not after work. Oh well.... I'm just gonna rock the thing.

I'll figure it out sooner or later.

If your interested, here's the "68" Squareback Saga from conception.

Oh .... & I'm Robert

raygreenwood · Post by **raygreenwood** » Fri Sep 12, 2008 6:43 am

You noted that it was cooler.....
Thats the ticket. You should try unplugging the intake air temp sensor and then re-setting your idle....or also check it with an ohm meter to make sure it is working correctly. Also check your CHT sensor wit han ohmeter both hot and cold. Ray

Eva65 · Post by **Eva65** » Fri Sep 12, 2008 4:58 pm

raygreenwood wrote:You noted that it was cooler.....
Thats the ticket. You should try unplugging the intake air temp sensor and then re-setting your idle....or also check it with an ohm meter to make sure it is working correctly. Also check your CHT sensor wit han ohmeter both hot and cold. Ray

You may be on to something there.

After I got it back together I had to reset the idle (it was really high) but I didn't unplugging the intake air temp sensor first. I see to it this week-end.

Thanks..!!

squarebackagain · Post by **squarebackagain** » Wed Oct 01, 2008 10:24 pm

Hey... I'm new here and am having a similar problem. The idle on my '70 injected Type III rolls up and down which I thought was a vacuum leak- but am unable to find the leak (new hoses etc). I am ALSO having a problem with fuel smelling exhaust in the cabin, so I believe I am burning rich. Are the problems related? No major exhaust leaks either. I live in Reno 3800 ft elevation, maybe this has been a problem for the air mixture?

raygreenwood · Post by **raygreenwood** » Thu Oct 02, 2008 11:50 am

I would bet that that there are more places to look for a leak than you think.
In a carburetted car a vacuum leak causes lean running. In a D-jet injected or MAP controlled fuel injected engine a vacuum leak anywhere between the TB and engine will cause RICH running.

The list is long for where possibel vacuum leaks are,
Inake runners to head gasket
Inake runners to plenum boots
TB return spring not seating or throttle cable too tight
The plate and gasket bolted onto the back of the plenum of teh type 3
The steel line and hose that comes out the bottom of the plenum that is near impossible to see.
The vacuum advance or vacuum retard lines.
The vacuum retard can unit itself
The auxiliary air regulator, poorly adjusted or worn out or leaking base gasket

Any vacuum hose to teh heads,
Valve cover gaskets
Pushrod tubeseals
Injector seals
The full load switch diaphram under the right hand fuel injection runners
Or....
Fuel pressure flucatuating
Ray

squarebackagain · Post by **squarebackagain** » Wed Nov 19, 2008 10:19 pm

What is a CHT reading?

raygreenwood · Post by **raygreenwood** » Fri Nov 21, 2008 11:47 am

The cylinder head temperature sensor. It is the small single wire sensor screwed into the left side head. It is responsible for a good part of your fuel mixture baseline. It reads about 2800-3000 ohms whne cold going down to about 70-100 ohms when hot. They get out of whack with age....and are about $30-40. Ray

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F.I. engine idle goes up and down.. up and down.. up and..

F.I. engine idle goes up and down.. up and down.. up and..

Idle goes up and down...up and down...up and down...