Poor running when cold
 

I have 2 problems that may or may not be related.

My 1985 (US) starts every time, after about 3-4 seconds of cranking. After it starts, it has a low, loping idle. It stays running and doesn't stall. Once it is hot, the idle comes up to around 800 rpm or so and smooths out and idles pretty well.

Another issue is that when the car is cold, acceleration is very rough and the engine almost seems to cut out at times, so much so that my head bobs forward when it misses. If I accelerate slowly, I can keep it fairly smooth. The colder it is, the more pronounced the problem is. When the engine gets hot, it runs and accelerates just fine.

Before I start guessing and changing parts, does anyone have any ideas where I should start? I have searched and can't find this particular problem.

Thanks.

I have seen this on other cars with that version of EFI - temp sensor was eventual culprit. On one car that fired injectors when the throttle was floored, I could only start it cold by turning on, flatten foot, pause, flatten, pause 5 or 6 times to get enough fuel to fire and run. Other posssibility, if you have an Aux Air Valve is that its not opening enough when cold . Pull the front hose off, shine a light in - cold you should be able to easily poke a pencil or large screwdrive through the valve. Mine started stalling in the first few minutes of run, and I opened up the AAV and adjusted the return spring a bit, and closed it up with M6 bolts. Only required a small adjustment to idle screw when hot, cold idle went up to 1100rpm.
jp 83 Euro S AT 57k (CIS)

Thanks J. I will see if I can find more info about the temp sensor. Given what I know about this car, I'm guessing there are several. I don't know my way around this engine room, yet.

Bill,
Somewhere there is a picture of an engine bay with pointers to most items of interest. There will be a temp sender for the gauge, and a separate sender for the injection ECU . Typically these temp things are NTC (negative coefficient of temp) devices, whose resistance goes down as temps rise. Typical cold ohms are ~3k, dropping to the 200-300 ohm range when hot. This should be in the WSM somehwere. In my experience the gauge sender has 2 small vertical spade tag connectors, where the ECU sender has std 1/4 tags, but dont quote me. There is also a 'temp-time" switch - horizontal in the water bridge, 2 tags, which controls the AAV - quite a bit of discussion on this , so a search will help.
jp 83 Euro S AT 57k

That is the "Temp II" sensor.
There are 2 sensors on the water bridge (the tube that runs across the front of the engine, right under the oil fill). The one on the left (driver's side) has 2 wires, That's the gauge & warning light. The one on the right (passenger side) has a single plug going to is. That's the Temp II. Search that term for a lot more info.

There's an underhood pic, with everything labelled. But I don't know exactly where it is. Hopefully someone who does know can post or link it.

Here is an "under the hood" post, but it is for S4+. A lot is still relevant to an 85 though.

https://members.rennlist.com/v1uhoh/underthe.htm

That has it. #2, with the blue plug.

Thank you.

Thanks, everyone. I hate throwing parts at a problem, but I am ready to place an order with Roger anyway, so I guess another $28 for the sensor is worth a shot. I am surprised that no else has had a bad sensor manifest itself the same way it may have in my car.

Bill, there's plenty of us that have had Temp II issues with similar symptoms as you. It's just that we haven't gotten around to reading your thread yet.
I think you are on the right track now and the Temp II is super easy to replace. You can do it without draining coolant and if you are fast, you won't even lose more than a few drops.:)

As was noted, lots of people have had this issue. Search "Temp II" or "Temp 2" and see how much comes up.

I fully agree that 'throwing parts' at a problem is not the best idea.
You can test your current temp 2. It's a simple resistance check. I don't know the correct ohms (cold, sorta hot & hot) off hand, but searching should find it. It's been discussed about a zillion times.

OP: Did you ever resolve this issue? I have what sounds like this exact same problem. Oddly, this happens reliably in the morning, even though "cold" was about 70F this morning. And it can sit all day at work and I will go out and it will NOT have this problem. Also, I replaced my Temp 2 a couple years ago, and this has been a problem with my car for quite a while. So I'd be surprised if that was the fix for my issue, but I'm definitely interested to hear if it was the fix for yours.

I have the same issue with my 928S euro of 1980. And all parts have been replaced or checked, except for the AUX air valve. At cold the valve
is just opened at the small square hole, so I suspect it is not enough air that can pass. I still need to check this.
But chances are very likely that this is also your problem.
My problem only lasts for 2 to 5 minutes till engine becomes warmer, depending on the outside temperature.

kr
Gerrit

Update: I replaced the Temp II sensor and it seems to be fixed. I drove it once after the repair, and it did not stumble when it was cold. The cold idle is now smoother, though not higher.

Thanks again for all the advice.

Thanks for the update. Sounds like I should take mine out and test it.

Update 2.0: The Sensor II did not fix the problem. I took it out this morning (temp in the 40s) and it stumbled like it wouldn't take fuel when I put my foot down until it was warmed up. Runs great when hot.

When I first replaced the sensor, it was a warmer day and it had been idling for a little while before I drove it. Back to square one.