No More Cold Start

[HibiscusB5_A4]

I have noticed the past couple of months that my car has not performed a true "Cold Start" (Holding the idle at 1100ish rpm) and then dropping below 1000. It is dropping right down to the 700-850rpm immediately. I am trying to figure out why this is happening. I read a few forums of people saying the weather is too cold for it to want to perform the function, but this has been happening in 32 degrees and 70 degrees, so I do not believe that to be true. Sometimes the car will idle at 16 or 17 AFR, after the initial morning startup of the day while I am still sitting in the parking lot. Then once I drive it and get to the stop sign 400 feet away at the other side of my parking lot it is back at 14.7-14.8 consistently and never leans out again... (I have seen 18 or 19 AFR after it has been driven, and I go to start it again) I do not suspect it is the tune doing this as it was cold starting fine and idling fine in the past for quite some time. And there are times I start it up, it fails to perform the cold start but idles at 14.7-.8 just fine all day. It is not a guarantee it idles lean, but it has been a guarantee of no cold start.

I had a friend suggest a thermostat issue, but it has no problem opening/closing, seems to perform as normal

Perhaps a vacuum leak? and the computer is adjusting for it once I do a little driving?

Smog/Evap Pump that usually whirrs to help warm it up dead?

I have a check light but is only for my HFC.

Thoughts?

[Cybersombosis]

What’s your coolant temp sensor showing when cold?

[HibiscusB5_A4]

It is all the way to the left when cold. As normal

[Cybersombosis]

I’m talking about what VCDS says it is when it’s cold. Go in to Engine, then advanced measuring blocks and type in temp and tick off engine temp and see what it says. The cluster temp is a different circuit on the same sensor.

[HibiscusB5_A4]

Gotcha, when I get my VAGCOM cable in my hands I will investigate.


Sent from my iPhone using Audizine Forum

[walky_talky20]

I just had a Coolant temp sensor failure myself (just the ECU side).

Dash gauge read perfectly normal, but ECU was usually reading FULL hot. Like 290F or something ridiculous. The car would need 2 or 3 tries to start with outside ambient temps below freezing. And then it would run like garbage until the wideband warmed up and enabled Closed Loop. The wideband was doing some *work*. LOL

I will say, your car "barely starting" COMBINED WITH the "barely drive away under its own power" is a surefire way to get some attention in the work parking lot. They can think I'm poor, I don't care. I'll change the stupid sensor when I feel like it.

[HibiscusB5_A4]

Would it be reasonable to assume my ECU side has also failed? Seeing that my gauge reads correctly on my cluster? I don't have any trouble getting the car to start it always cranks and fires up great, it just doesn't hold that rpm up and trigger that EVAP pump whirrr like it normally would. My chassis is starting to show its age electrically... even when it's cold enough out my windshield wipers start going all by themselves and it's a battle to get them to not stop in the middle of my windshield haha.


What difference is it replacing the ECU side of things rather than the sensor behind the head? Same deal just different spot? Probably less coolant going everywhere.

Thank you for the chuckle lol.

[walky_talky20]

It is actually 2 sensors within the same sensor housing. That is why it has 4 pins. 2 pins for Dash Gauge, 2 pins for ECU.

You can confirm the issue using VCDS by comparing the Coolant temp reading in the Instrument Cluster measuring blocks to the Engine Computer Measuring Blocks. They should agree within probably 1 degree C.

Do note that the high-idle portion of a cold start routine is not guaranteed. There is only a certain temperature range where it will do this. If it is colder or hotter than that range, then the high idle is not requested. There's probably a Motronic ME7 EFI Strategy document that describes the exact temperatures and factors that play into this.

[HibiscusB5_A4]

I see, it has always performed the high idle for the past 4 years so when it suddenly stopped for an extended period of time, I assumed something was up. When I get ahold of my VCDS I will get to the bottom of this. I appreciate the input!