Ok, so here's another issue with my 1974 2L. I have a rough idle, feels like the car is missing. Not quite a dead cylinder, just like there's a partial miss.

The really odd thing is that as the RPMs approach around 3000, the miss goes away, and suddenly, almost as if I flipped a switch. And it is not throttle position -related because it does the same thing if I keep the throttle at the same place as the revs rise. That transition from rough to smooth is much more noticeable when it's cold.

And when it's cold it really almost feels like my Integra engine does when it goes from low cams to high VTEC cams.

Once the engine warms up the transition is less pronounced, but any time I'm in a gear where the RPMs are below 3000 (say, around 55 mph in fifth gear) the miss is there. Upshift to get the revs above 3k and it's fine. Increase speed to where the RPMs are above 3k (65+ in fifth) it's fine.

Other than that, engine is fine.

I replaced the TPS PCB (for other reasons) and adjusted it per the guides, and that seems fine.

I'm wondering if it has something to do with a timing change internal to the distributor, maybe mechanical advance? Otherwise if it's fuel-injected related I'm kinda lost, as my injection knowledge experience started with the K-jet in my old Rabbit and is currently all about EFI (Honda and Megasquirt).

Thoughts appreciated.

- Greg

My '70 1.7 had a problem idling when cold. It was kinda hard to keep it running until it warmed up. But, during the warmup phase, it was like your light switch analogy at around 3k rpm. I replaced the temp sensor, and it will at least idle now, but without the thermostat, it still takes a while to warm up.
If your problem persists even after warmup, I would suspect a distributor problem, IF it does warm up completely.

cm

Thanks for the feedback. It's an interesting thought; I've seen the bellows compressed when I'm under the car and it's cold, but I've never verified proper operation when it's hot (nor verified the cables/doors are working). And, the temp gauge on the dash (the one in the fuel gauge) rarely comes much above the left hash mark...

Excuse my ignorance, but what temperature sensor, and where is it? If it's not too expensive I don't mind buying one to try. And I'll check the proper operation of the thermostat/bellows as well.

- Greg

I also have some rough running during warm up. I just replaced my injector connections (electrical). they didn't feel like there was a positive connection at two of them. One would pop out with engine vibration. I hope that will help.

I know it's dangerous but I'm assuming dwell and timing are correct...

The other thing to check is the Aux air regulator. It allows extra air into the engine during warm up. With the engine cold, if you pull the vac. hose off the AAR (the one on the drivers side) and the idle jumps up, you probably have a bad AAR. It should be open and allowing the extra air in, but isn't. Taking he hose off mimics the open AAR. after a few minutes the AAR will warm up and close. bringing idle back to normal, around 900RPM



As far as temp sensors, there are 2.
1) Oil temp sensor- bottom of engine near bellows thermostat. Not your issue here.
2) Cylinder head temp sensor- under the engine tin by the #3 spark plug. Would be a problem if its too hot or faulty. No start/run condition. I don't know how this would effect idle but probably the one to look at.

A good/bad bellows therm. Won't effect idle. They fail in the max cooling mode. So it may take longer to fully warm up.

Good luck,
bob.

what are your compression numbers?

In my repair manuals, it's called "temperature sensor II", and is screwed into the head adjacent to #3 spark plug. Not expensive, as I recall.
"Temperature sensor I" is for intake air temp.
Oil temp. is an important, but optional, gage-only parameter.
Temp. sensors I & II feed signals to the efi control unit, monitoring engine warmup.

cm

"The really odd thing is that as the RPMs approach around 3000, the miss goes away, and suddenly, almost as if I flipped a switch"

That is just about the rpm that the diz is at full advance. I would suspect the distributor needs a good cleaning. When is the last itme you adjustd valves, set dwell, and timing? In that order. Setting the tps will have little or no affect if those items are not tended to. The idle adjustment knob will have no affect either if the tps is maladjusted. Evrything depends on everything else.

As for the cold issue; with engine running and cold, remove the hose on the passenger side of the air cleaner that goes to the AAR and use your thumb to feel for vacuum. No vacuum means your AAR is stuck closed.

"Everything depends on everything else"...exactly.

AAR has been REMOVED from this car. No idea why. But that's not the issue, as it continues to run rough below 3000 RPM well after the AAR would be fully closed.

Compression numbers are "good"; I had the car checked out by RacerChris after I bought it. Can't seem to find the spec sheet he gave me...

Valves, dwell, and timing were all done by RacerChris a couple months ago at the same time.

Pelican shows those temp sensors - both gauge and head - are NLA...

I think I got mine from AA. It's been a while, and I don't know if they changed the part over the years/engines.

cm

Sorry, just caught this...who's "AA"?

- GA

http://www.autoatlanta.com/porsche-parts/p...e_914_parts.php

Gimpy #2 injector. Chris/Ed at Tangerine Racing found/replaced it.

Man, it runs smoooooooth now....