I'm at my wit's end and need some help solving this problem. 76 914 2.0L starts and runs well cold. RPMs up around 1800 and reacts well to throttle. Once the engine warms up, idle comes down to about 1100 and is fairly steady. However throttle now causes immediate hesitation (bogging) followed by backfire and rough running up to 3000rpm. Over 3000rpm is much better. When I bring the rpm up to 2500 and attempt to hold it there, engine stays at 2500 for a second or two then drops down to 1500 and then goes back up to 2500 and continuously cycles up and down. (I believe vacuum leaks cause the engine to surge UP in rpm then down. This is reverse. It stalls downward then back up) This engine was rebuilt about 10 years ago and has roughly 4000 miles on it.

this is what has been done to date:

1: Replaced the CHT sensor.
2: Replaced all vacuum hoses.
3: Replaced all engine fuel lines.
4: Had injectors cleaned and tested.
5: Had CS valve cleaned and tested.
6: New injector seals.
6: New CS valve gasket
7: New intake manifold gaskets
8: New intake manifold boots
9: New throttle body gasket
10: Removed and inspected plenum. All ok
11: New Throttle positioning switch. Also adjusted.
12: Checked MPS. Both resistances and vacuum good. 20" held no change
13: Checked vacuum on decal valve. 20" held. Opens at 15 or 16
14: Checked Aux Air valve. open when cold and closes after 10 min run time.
15: Checked dwel angle. Good
16: Checked timing. right dead on the notch
17: Checked valve clearance. Good
18: New distributor leads
19: Cleaned distributor rotor and cap. (did not change contacts yet)
20: Checked all resistances at computer terminals and all are good.
21: Checked fuel pressure and steady at 29
22: After engine warm attempted to try different Computer knob positions / bleeder screw settings but have no CO meter. It runs best with computer knob turned all the way Clockwise.

After all this, it still runs the same way. #$^@$&%#%&@$%

My only other thoughts are to change the distributor contacts, check the adv/ret vacuum and perhaps play around with the timing.

I've heard the throttle body could also cause vacuum leaks but not sure how/what to check.

Any help/suggestions would be greatly appreciated (and desperately needed!!)

Centrifugal advance weights sticking? Lubed the dizzy weights? 1 drop 30 wt oil every year, in the recess at the center of the dizzy shaft.

...seems like you got most stuff covered...but need to ask just a couple questions:

is this car new to you.... did it ever run well?
who did all that work?

I'm close by, I'm sure we'll figure it out.

Tell us more about checking the timing. What does right dead on the notch man?

Distributor advance plates stick when engine heats up and 40 year old grease turns into glue.

Remove advance plates, take them apart, clean them off with degreaser, relube with wheel bearing grease.

Ray Mital did a great job documenting how to do this.

That will be next on the list. Thanks...

I have owned the car since the early 90's and rebuilt the engine in the mid 90s. Ran well for many many years. This is a new problem that just came about this summer. I did all the work noted above. Will check out the distributor etc... as recommended.

As far as checking the timing, ran engine until hot, removed adv/ret hoses from distributor, ran engine to 3500rpm and checked timing with light through access port to fan. Fan has notch on it that lines up with the notch in the housing casing.

Willing to accept any help possible to those local to me.

How can I get this documentation from Ray so I can do this?

Ray will dig it up for you.

So I removed the Distributor to find it was not functioning very well. Sticky and rusty. Also vacuum diaphragm is cracked and leaking. Looking for trigger contacts and replacement vacuum unit. Anyone out there who can help? OR who can rebuild dist. complete???

Take the diz cap off and read the number on the little arm coming from the vacuum can. That's the unit you need. I would also suggest a new set of trigger points. They may look fine, and have good continuity, but still not work. I just chased this same problem.

You check for the condition/presence of the seal on the 710 cap?

THE SAGA CONTINUES.....

So I happen to find a '76 distributor w/ Vac. Can in great shape. Checked out and installed. Decided to check all the items AGAIN just to make sure no leaks including the new hoses. MPS good, Decel good, Dist Vac Can good, Aux Air good. Tightened all hose clamps on new hoses including intake boots. Torqued intake nuts/gaskets.

Started car. Idle was initially high around 1800. After warm up came down to 1000. Checked dwell with new Dist. and at 50. Checked timing and at 27 degrees. (also at idle, the white dot shows up right at the notch)

So I rev up the engine and it STILL has a leak. Ramp up to 2000 and it won't hold. Bogs down to 1000 like it takes in a huge gulp of air then bumps back up. It is intermittent. Sometimes engine holds speed and then POW!! Sucks in air and drops.

I took a propane tank and checked all around every part of the intake, plenum, etc... No change at idle. Couldn't really do the propane and rev the engine at the same time.

Fooled around with the throttle body and it seemed to change the idle rpm when I rock the shaft back and forth or pushed it axially. (doesn't really move much)

Could a "gulp" of air come from a worn throttle body shaft? Has anyone experienced this problem before? Does anyone know how to rebuild a throttle body and where to get parts?

I REALLY WANT TO SOLVE THIS PROBLEM BEFORE WINTER!!!

Had similar issue- discovered, as I took the FI system off to replace with carbs, I discovered a prominent leak in the plenum.
May eventually return the car to FI, but for now,it's running well on carbs.

Could your throttle body have a crack in it?

The hole for the throttle shaft can wear, causing leaks. That's a well-known problem on 40+ year old carbs; it may be getting to be an issue with throttle bodies as well. The late Mike Cooley had a setup to install oilite bushings for the shaft, but he sold off the tooling. (And trying to make it work with the wrong tools didn't exactly work.)

A good machine shop can do the same.

No idea if it is contributing to your problem, though.

--DD

Update. Took the throttle body apart and found the shaft was slightly worn but the body where the shaft goes through was worn. Don't have a fix for that yet so sealed the areas as best I could and put it back on. Noticed the outer TPS arm was bent when I was reinstalling. This was part of the problem and the engine is running much better now. However the idle still is not steady. Not sure if the middle arm of the TPS is in the correct position at idle. Does anyone have a photo of a TPS with the cover off showing the correct positioning of the arms at idle they could post to this thread?

Does this help?

http://www.914world.com/bbs2/index.php?s=&...t&p=2161741

Hell yes!!! Thanks... This website is great!! Will check it tomorrow. Also going to cap the air pump ports at same time. Have seen a few threads that state the thread on top of air ports are 3/8 or 1/4 but that doesn't seem right to me. Anyone know war size brass cap I need?