ltoolio

Just got done doing a bit of a dash / console refresh, and I'm finding that my idle is running really rough. It's quit on me a couple of times, but there are never issues when I'm in gear and driving.

Some additional points:

1. My work revolved around tightening things up on the console...
2. Did some patch-work on some loose connections. Really just provided better crimps / junctions for some gauge wires. Nothing monumental, and I feel very confident I left any connections in a better place than they were.
3. I did not bother hooking the connectors up to the Heater Control Unit. I do not have AC any longer in the vehicle (PPO completely removed it), and I have no need for heat.
4. The new console I received did not have the Behr Vent unit (not sure how to describe it, but picture is below). I've looked through the WSM and have not been able to find it. However, it has left me with two orphaned (vacuum?) lines which are not currently connected to anything.
5. At start, the battery gauge hovers around 10 V, but stays constant at 12 once driving. I don't recall if it acted the same prior to my work.

I'm going to retrace my electrical steps just to see if I missed anything, but might the issue be item 4? I'll also be calling to get a new Fuel Pump relay as an excuse to replace it (it hasn't been done so in at least the last 9 years).

As always - thanks for the input.

Oops. Here's the pic:

OTR18WHEELER

Are you sure you didn't leave any vacuum lines open, my first guess is that you have a vacuum leak.

ltoolio

Well, that's my guess. The lines go into the Behr piece in the picture appear to be vacuum lines, so I'm thinking I need to go in and join them with a coupler.

ltoolio

Update on this, and unfortunately not what I was hoping for:

Ended up replacing the battery ground and engine ground via a suggestion in a separate thread. Cleaned the ground points for those very well as long as the other ones on the car, and idle continues to be very rough.

I had it up on jack stands, so didn't want it to shudder to the point of dying, but I think it was heading that way.

The odd thing - the "Stop Light" lamp was lit once when I was idling, and it was not after a stop / restart.

Might that point towards an electrical issue? I've double tracked my connections under the console, and all looks good (and even better) than when I first started doing work there, but that's about all I can come up with at the moment.

I need to record the various rpm / afm / etc readings throughout, and I'll do that at some point soon. Sleep needs to come now.

OTR18WHEELER

ok then, if not vacuum related, and you think it may be electrical,.. that may be.

on occasion I have had a rough idle, I have done the intake refresh and fuelline stuff, but one gremlin that has not been solved, as I have not done any pod/inst cluster work yet, remains.
?when you encounter the rough idle, is your tach working?, once in a great while, mine will idle a little rough, also the tach is dead, A sharp slap on top of the pod revives the tach, and the idle smooths out., and everything is fine.

Jetdriver69

I had about the same symptoms on my 82 5 speed.

Try disconnecting the L Jet brain in the passenger foot well and reconnect after a few minutes. Don't ask me why it helps, maybe resetting to a null value.

This seemed to work on my 82 until I cracked open the AFM and adjusted the wiper arm. Mine had a worn part of the track and by moving the wiper arm back about 1 mm, the arm runs on a fresh piece of resistor material.

There are tutorials on you tube for a 944, but it is essentially the same AFM.

Runs great now.

ltoolio

You bring up a point that I should have revisited...

Would the vacuum lines behind the console affect the idle? If so, we may be onto something.

I'm not confident in the seatings of the vacuum lines into the vacuum block under heater vent area, so if those could affect the idle I may need to go back in and do a re-eval.

I'll give that a try, too. Easy enough.

Thanks to both.

ltoolio

Just re-read and realized I didn't respond to this.

Yeah...Tach is always working. Just starts to bounce as the car starts to go rough, and then dies (not surprisingly) when the car dies.

The Deputy

Did you get fuel somewhere out of the ordinary?

I picked up a full tank of bad fuel a few weeks ago, car ran terrible on an idle and "just wasn't the same" during acceleration. While driving the issue was less noticeable, however, you could sense it wasn't totally the same...since it took a bit more throttle to get it moving. At every stoplight, it felt as tough it would stall, but I just kept it a higher idle to compensate.

Finally got down to a half of tank and filled it up somewhere else, that has a much better turn over of fuel sales, and the car ran better within the first mile...then was about normal by the time I got home (35 miles). Ended up taking the car for a nice long ride with the 50/50 fuel mix and ran it down to nearly empty. Refilled with a whole new tank full...and the car drives like a dream again.

Brian.

ltoolio

Well, that's a bit hard to answer, as I've only filled it up once since I've owned it and the same gas is sitting in the tank right now.

But good thought...maybe it was a bad batch to begin with. The station I went to was a BP with a pretty high-turnover rate, and I've got a bit of a ways to go before hitting a half tank. Sounds like a good reason to take her out for a bit of a lengthy drive.

fiatrn

Itoolio
IF I read this right, you took something apart, and after re-assembly the car did not idle as well. You did not rehook the lines going the circled part in the photo.

Most likely it was something from when you worked on the car. Doubtful that something else, be it gasoline or computers, would go wrong at just that same time unless it was related.

That part is a vacuum actuator, and if you left the lines off you now have a vacuum leak. It may be a very small leak, and not enough to make it stall all the time, but there's now a vacuum leak.

Fix that and you will most likely fix your idle problem. Also, if there was some electrical connector that you left loose, you'll find that in the process of fixing the vacuum lines.

Best luck

Jonathan
The FiatRN

ltoolio

Thanks RN.

I have since plugged joined the two lines that connected to the actuator, but the problem persists.

That said, you answered one of my lingering questions here - would a vacuum leak in the console affect the idle, and it sounds like the answer is yes.

Would a leak in the vacuum line lead to a high AFR?

greatwhitekc

First Gremlin?

Hey buddy, this is a Porsche 928 site!

But seriously, I had a friend who had a Pacer.......

fiatrn

"Would a leak in the vacuum line lead to a high AFR? "


Short answer: yes.



Most cars I've worked on (all? Not sure - there may have been some wacko Lancia with a vacuum pump) use the engine intake to create vacuum, be it for emissions control or fuel pressure regulation or brake boosters. If the vacuum leaks, air gets into the system. Depending on where that air goes, it can cause trouble.

If the air gets pulled into the system from after the point where air is measured, then it can lean the fuel air mixture. For example, on my car with multiple carbs (an old Fiat) only one carb bore has a vacuum port for the charcoal cannister. If that port leaks, then that one carb bore runs lean and the carb appears maladjusted and the engine idle suffers until the leak is fixed (or, worse, the cab adjusted to compensate, which will eventually come back to bit you).

The same could happen to an engine with independent throttle bodies, if you lost vacuum from one port or something.

I don't have enough experience with the 928's vacuum system to know where it pulls vacuum for the heater controls, but I'm gonig too soon bc I have to hunt down a combination of misbehaving heater controls and an oddball idle. Neither makes the car unusable, just occasionally misbehaved, and probably related.

The Deputy

I wouldn't "totally" discount the fuel. My car was absolutely fine after filling it up. Drove home the entire five miles from the gas station, without any problems. Problem didn't really appear until I started it six days later and progressively got worse.

I get what you’re saying about the vacuum lines, but it could be a coincident.

Brian.