Rough Idle and Misfire cold start

Hi everyone and thanks in advance for any help offered.

I've been searching through this forum and google for any reason as to why this is happening

Issue:
When I start the car after more then 5 hours (seems when engine temp drops below 50 degrees)
- Engine idle is rough and fluctuates between 750 and 900 rpm
- Everytime it drops the headlights get dimmer/brighter
- When I try to take off, the engine bucks like a horse and I have to force the revs over 2200 until the bucking becomes unnoticeable (feels like misfire?)
- All cabin lights flicker as if I'm at a rave
- Radio randomly cuts out (aftermarket)
- Randomly car will beep at me and handbrake light and abs light will come on for 1 second. (usually occurs 1-2 times)
- No Error codes are thrown
- Once temp meter hits 50 engine runs normal and all lights stop flickering

Things I've done
- Someone here suggested cleaning the ground contacts, I cleaned the positive contacts on the alt and grounds under the battery
- Checked connectivity with voltmeter of positive on alt to positive on bat terminal, and connectivity of ground on bat to alternator and engine block and body. All seems good
- Replaced Alternator (as it was not charging past 13, now charges at 13.8 under load)
- Replaced fuel filter and ran Ligui molly Diesel injector cleaner.

Please note I only have the standard OBD2 tool and not a VCDS

Any suggestions would be greatly appreciated.

Sounds like you need a new coolant temp sensor

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Why would you say coolant temp sensor, it must be identifying the temp as my temperature gauge works and the rough idle stops when the gauge reads past 50 C?

In any case I will see how much it costs at my parts store, seems like an easy replacement.

Glow plugs are supposed to activate at 48 degrees. ECU doesn't know this because of bad cts. The part is cheap and easy to install. That's my theory anyway.

If you unplug the sensor (back ds of head) you can verify that's the problem since the ecu will default to a cold start map.

ilikepie911 said:

Why would you say coolant temp sensor, it must be identifying the temp as my temperature gauge works and the rough idle stops when the gauge reads past 50 C?

Click to expand...

The temp sensor is 2 parts.
One part for the gauge the other for the ECU.

When the car is cold use your 'standard OBD2 tool' to look at group 001 to see if the coolant temp matches the outside temp.

Sorry for no action here, have been a bit busy with work and stuff. I will give it a try this weekend. I'm using Torque pro. I'll give it a shot tomorrow and update with the results.


Thanks for all the responses.

Update... Finally got around to replacing the sensor, Went to replace it but I cocked it up lol. Tried to do the quick swap but the rubber seal from the old one was stuck inside and I didn't know it.. lost all my coolant before I figured it out. Anyway got the new one in seated and clipped in, but I can't fit the plug back on. It slides in part way but I get a lot of resistance and am unable to get it to lock.

I tried forcing it but it just wont lock. It seems like there some orange rubber seal that compresses but I just cant get it to compress to lock in. I'm so frustrated at this I can't see straight!

Any help would be much appreciated.

Update... Still any suggestions on getting that plug back in would be great. For now I zip tied it real tight. The car isn't throwing any errors.


Started it this morning and found it was still having the same symptoms. Rough idle for a while on start up and flickering disco dashlights. I was reading through another site that said it could be my injector harness??

I would check the grounds under the dashboard or above the lower cover.
I think there are 2 in that area.

Also if the battery ground under the battery tray is bad then anything that grounds to the body is bad. (long shot)

I checked the grounds under the dash, and it seems ok. Tightened it anyway. Also checked the ones under the battery tray. They looked ok but I sanded them and the terminals for good measure... still the same issue...